bicycle brake adjustments

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Most brake problems result from excessive friction or poor installation of the cables, not poor setup, or poor quality brakes. Also see the article on cables for information on cable selection and adjustment of brake cables and brake levers . Direct-pull vs Traditional Cantilever Brakes Traditional cantilever brakes used two cables, a main cable running down the centerline of the bike, and a second, "transverse" cable connecting the cantilever units on each side of the wheel. The main cable would pull upward on the middle of the transverse cable, causing the cantilever units to rotate inward. The "direct pull" cantilever, also commonly known as the "linear-pull brake" or under its Shimano trademark name "V-Brake" is a simpler design, using only a single cable. The cable housing connects to one arm, and the inner cable runs across the top of the tire to the opposite arm. When the brake is applied, the housing pushes on one cantilever while the inner cable pulls the other. Since the cable runs straight across the top of the tire, direct-pull cantis need longer arms to get the cable high enough to clear the tire. This increases the mechanical advantage of the system, requiring the use of special matching brake levers . Quick Release Normal Position

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Page 1: Bicycle Brake Adjustments

Most brake problems result from excessive friction or poor installation of the cables, not poor setup, or poor quality brakes. Also see the article on cables for information on cable selection and adjustment of brake cables and brake levers.

Direct-pull vs Traditional Cantilever Brakes

Traditional cantilever brakes used two cables, a main cable running down the centerline of the bike, and a second, "transverse" cable connecting the cantilever units on each side of the wheel. The main cable would pull upward on the middle of the transverse cable, causing the cantilever units to rotate inward.

The "direct pull" cantilever, also commonly known as the "linear-pull brake" or under its Shimano trademark name "V-Brake" is a simpler design, using only a single cable. The cable housing connects to one arm, and the inner cable runs across the top of the tire to the opposite arm. When the brake is applied, the housing pushes on one cantilever while the inner cable pulls the other.

Since the cable runs straight across the top of the tire, direct-pull cantis need longer arms to get the cable high enough to clear the tire. This increases the mechanical advantage of the system, requiring the use of special matching brake levers.

Quick Release

Normal Position

Page 2: Bicycle Brake Adjustments

Boot Pulled Away

Noodle Unhooked

For wheel removal, the noodle may be unhooked from the arm link. This will allow the brake shoes to open up wide enough to clear even a fat tire. First, pull the boot away from the end of the noodle. Then squeeze the brake arms together with one hand while unhooking the lower end of the noodle from the keyhole-shaped slot in the arm link.

Make sure to hook the brake back up immediately after you re-install the wheel!

Parallel-Push Linkage

Page 3: Bicycle Brake Adjustments

Shimano's XTR and XT V-Brakes feature a special parallelogram linkage. This serves two purposes: It causes the brake shoes to remain at the same angle to the rim throughout the stroke, and throughout

the service life of the pad. It causes the direction of motion of the brake shoes to be close to horizontal, rather than the usual slanted

arc centered on the pivot boss. This is a major advantage with very fat tires on narrow rims, because it prevents the shoe from rising up and damaging the sidewall of the tire on release, and also prevents having the brake shoes dive under the rim as they wear down.

Unfortunately, the extra pivots considerably complicate the mechanism, and this has caused maintenance problems and excessive squeal in practice.

Direct-pull Brake Adjustment

First, remove the arms from the studs, and make sure the studs are free of rust. Coat the studs liberally with grease (this is VERY important!)

Install the arms with them at their maximum spread and tighten the bolts that hold them to the frame. This is how you set the springs.

Shoe adjustment is covered in the article about rim brakes, but there are a few special things about direct-pull brakes:

Most direct-pull brakes use threaded-stud type brake shoes. Use the kind with spherical washers to allow full adjustability.

The brake shoes only need to be extended inward from the brake arms if the brake arms are too close together at the top, interfering with the tire or allowing too little cable travel.

Unless the brakes have a Parallel-Push linkage, adjust the shoes initially so they are near the top of the rim's braking surface, to allow them to migrate farther downward before risking a dive under the rim.

Page 4: Bicycle Brake Adjustments

If your brakes use the Parallel-Push linkage, the pivots may need servicing. There are special kits for this.

 

Centering

When the brake is released, the brake shoes retract away from the rim. Ideally, the shoes on both sides should back off by the same amount. If they don't, the brake is not properly centered. In extreme cases, one of the shoes may not retract, and may rub on the rim even when the brake is not being applied.

If a brake appears off-center, check first that the wheel is installed straight in the frame/fork. If the wheel is crooked, and you maladjust the brake to compensate, you are creating two problems where there was only one before.

Spring Adjustment

If your wheels are centered, and your brakes are not, and, if the pivots are properly lubricated and free-moving, the brake shoes should be centered. If they are not, you probably need to adjust the spring tension on one or both of the cantilevers.

Most direct-pull cantilevers have adjustable spring tension. The adjustment will be a small screw with the head facing outward to the side of the bike. The screw is generally located near the bottom of the cantilever, below the pivot point. Sometimes it works with a Phillips screwdriver; other times, a small Allen wrench may be needed.

Page 5: Bicycle Brake Adjustments

Tightening this screw tightens the spring, so you want to tighten the spring of whichever arm is too close to the rim. This will make it spring back farther.   

o About Rim Brakes o Direct-Pull vs. Traditional o Quick Release o

o

o Parallel Push o Adjustment o Centering o Brake Levers o Compatibility

About Rim Brakes

Direct-pull brakes are a type of cantilever rim brake. In connection with this article, please read the lead article about rim brakes. It covers, among other things,

Why Rim Brakes? Rim Brake Types Centering Mechanical Advantage Noises/Squealing Shoe Types

Page 6: Bicycle Brake Adjustments

Shoe Adjustment

Most brake problems result from excessive friction or poor installation of the cables, not poor setup, or poor quality brakes. Also see the article on cables for information on cable selection and adjustment of brake cables and brake levers.

Direct-pull vs Traditional Cantilever Brakes

Traditional cantilever brakes used two cables, a main cable running down the centerline of the bike, and a second, "transverse" cable connecting the cantilever units on each side of the wheel. The main cable would pull upward on the middle of the transverse cable, causing the cantilever units to rotate inward.

The "direct pull" cantilever, also commonly known as the "linear-pull brake" or under its Shimano trademark name "V-Brake" is a simpler design, using only a single cable. The cable housing connects to one arm, and the inner cable runs across the top of the tire to the opposite arm. When the brake is applied, the housing pushes on one cantilever while the inner cable pulls the other.

Since the cable runs straight across the top of the tire, direct-pull cantis need longer arms to get the cable high enough to clear the tire. This increases the mechanical advantage of the system, requiring the use of special matching brake levers.

Quick Release

Normal Position

Page 7: Bicycle Brake Adjustments

Boot Pulled Away

Noodle Unhooked

For wheel removal, the noodle may be unhooked from the arm link. This will allow the brake shoes to open up wide enough to clear even a fat tire. First, pull the boot away from the end of the noodle. Then squeeze the brake arms together with one hand while unhooking the lower end of the noodle from the keyhole-shaped slot in the arm link.

Make sure to hook the brake back up immediately after you re-install the wheel!

Parallel-Push Linkage

Page 8: Bicycle Brake Adjustments

Shimano's XTR and XT V-Brakes feature a special parallelogram linkage. This serves two purposes: It causes the brake shoes to remain at the same angle to the rim throughout the stroke, and throughout

the service life of the pad. It causes the direction of motion of the brake shoes to be close to horizontal, rather than the usual slanted

arc centered on the pivot boss. This is a major advantage with very fat tires on narrow rims, because it prevents the shoe from rising up and damaging the sidewall of the tire on release, and also prevents having the brake shoes dive under the rim as they wear down.

Unfortunately, the extra pivots considerably complicate the mechanism, and this has caused maintenance problems and excessive squeal in practice.

Direct-pull Brake Adjustment

First, remove the arms from the studs, and make sure the studs are free of rust. Coat the studs liberally with grease (this is VERY important!)

Install the arms with them at their maximum spread and tighten the bolts that hold them to the frame. This is how you set the springs.

Shoe adjustment is covered in the article about rim brakes, but there are a few special things about direct-pull brakes:

Most direct-pull brakes use threaded-stud type brake shoes. Use the kind with spherical washers to allow full adjustability.

The brake shoes only need to be extended inward from the brake arms if the brake arms are too close together at the top, interfering with the tire or allowing too little cable travel.

Unless the brakes have a Parallel-Push linkage, adjust the shoes initially so they are near the top of the rim's braking surface, to allow them to migrate farther downward before risking a dive under the rim.

Page 9: Bicycle Brake Adjustments

If your brakes use the Parallel-Push linkage, the pivots may need servicing. There are special kits for this.

 

Centering

When the brake is released, the brake shoes retract away from the rim. Ideally, the shoes on both sides should back off by the same amount. If they don't, the brake is not properly centered. In extreme cases, one of the shoes may not retract, and may rub on the rim even when the brake is not being applied.

If a brake appears off-center, check first that the wheel is installed straight in the frame/fork. If the wheel is crooked, and you maladjust the brake to compensate, you are creating two problems where there was only one before.

Spring Adjustment

If your wheels are centered, and your brakes are not, and, if the pivots are properly lubricated and free-moving, the brake shoes should be centered. If they are not, you probably need to adjust the spring tension on one or both of the cantilevers.

Most direct-pull cantilevers have adjustable spring tension. The adjustment will be a small screw with the head facing outward to the side of the bike. The screw is generally located near the bottom of the cantilever, below the pivot point. Sometimes it works with a Phillips screwdriver; other times, a small Allen wrench may be needed.

Page 10: Bicycle Brake Adjustments

Tightening this screw tightens the spring, so you want to tighten the spring of whichever arm is too close to the rim. This will make it spring back farther.   

Brake Levers for Direct-pull Cantilevers

Direct-pull cantilevers have double the mechanical advantage compared with traditional brakes, so they require special brake levers. Direct-pull brake levers pull the cable twice as far, half as hard. The lower mechanical advantage of the lever compensates for the higher mechanical advantage. of the cantilever. It is not generally safe to mix and match levers/cables between direct-pull and other types for this reason.

Conventional brake levers used with direct-pull cantilevers will usually not pull enough cable to stop in wet conditions without bottoming out against the handlebars. In dry conditions, they either won't work, or will grab too suddenly.

Direct-pull brake levers used with any other type of brakes will feel nice and solid when you squeeze them, but due to their lower mechanical advantage you'll need to squeeze twice as hard to stop as you should, so unless you are a lightweight rider with gorilla-like paws, this combination isn't safe either.

Drop-bar Levers

To make a brake lever with low enough mechanical advantage for direct-pull cantilevers, the cable must run twice as far from the lever's pivot point. This is easy enough to do with levers for straight/upright handlebars. Levers for drop handlebars are harder to configure for direct-pull brakes, and currently, there are only a couple of drop-bar levers made that are compatible, the Dia Compe 287V and the Cane Creek SCR-5V "Æro" levers.

Most newer drop bar bikes are have Ergo or STI brake/shifter units as original equipment. Direct-pull cantis are not compatible with these. Other types of shifters may of course be used, along with the special brake levers. In any case many cyclists prefer bar-end shifters. These are simpler and less expensive than brake-lever shifters, and give an indication of what sprocket is in use: brake-lever shifters return to the same position after every shift.

Drop-bar Workarounds

If you want to use Ergo or STI brifters with direct-pull cantis, there are two workarounds available:

You can use a pulley-device, such as the QBP Travel Agent (Q.B.P. Photo). These are a bit of a hassle to set up, but do work. Any pulley of the small diameter commonly used on bicycles eventually leads to fatigue failure of the cable, so check the cable regularly for fraying.

If you have a bike with skinny tires and no fenders, there are "shorty" direct-pull cantis that are more-or-less compatible with drop bar levers.

Neither of these systems is ideal, and neither is really any better than traditional center-pull cantilevers.

BICYCLE REPAIR

Page 11: Bicycle Brake Adjustments

 

While bicycle brakes offer excellent stopping power, over time the cables may stretch, the brake pads wear and a pad might drag on the rim. Because your safety depends on optimum braking, here are guidelines for common adjustments to ensure that your grippers are always at their best.

Please note: These instructions are for conventional brakes, not disc brakes. Also, because brakes are so important for safety, do not work on your brakes unless you’re confident in your ability to do the job right. And, keep in mind that in order for brakes to work properly and to make the adjustments explained in this article, the wheels must be true and round (no side-to-side wobbles, up-and-down hops or bends).

Click here to learn more brake adjustments.

Tightening the BrakesFor off-road, comfort, hybrid and city bikes with upright handlebars; look at the brake levers for a handy device called an adjusting barrel (photo).

It will have a knurled edge for easy gripping and it makes adjusting your brakes easy without tools. It’s perfect for making your brakes feel like new after you’ve logged a good many miles and worn down your pads. And you can even use it on rides if your brakes begin to feel weak as sometimes happens when it's muddy or wet.

To use adjusting barrels, turn them counterclockwise by hand and check the setting by squeezing the levers. When the brakes feel right, lock the barrel adjusters in position by turning the lockring (the second knurled piece) clockwise until it's tight against the lever.

On road bikes with dropped handlebars, you’ll find the adjusters on the brakes (photo below). To tighten the brakes, turn the adjusters in the direction that moves the pads closer to the rims.

Keep in mind that when your brake pads wear out, the adjusters won’t do any good and you’ll need to turn the adjusters all the way back and replace your brake pads.

Wheel CenteringOne of the most common brake problems is a dragging brake pad; one that remains against the rim or stays close to it after you’ve released the brake lever.

The most common cause of this problem is a misaligned wheel. This can occur when you reinstall your wheel after removing it to put your bike on a roof rack or to fix a flat tire, and you don’t get it exactly centered in the frame.

Page 12: Bicycle Brake Adjustments

This causes the brake to work improperly because it’s tight on the frame and has been adjusted to align properly only on a perfectly centered wheel. Now that the wheel is crooked in the frame, the brake can't work correctly.

To correct the dragging shoe, simply center the wheel in the fork or frame. For most wheels, all that’s usually required is loosening, making sure they’re fully inserted in the fork or frame, and tightening them. (If the bike is standing, just press down on the handlebars for the front wheel and the seat for the rear wheel to push them fully into the frame and center them.)

If you have a frame that lets you place the rear wheel in different positions, check that the wheel is centered between the seatstays and chainstays before tightening it. You can do this by looking at it or use

your fingers as “feeler gauges” by sliding the same finger on each hand between the frame and rim or tire feeling if it’s centered (photo; the brake was removed so you can see the details).

Brake CenteringIf your wheels are centered and the brake still drags, the brake may have gotten bumped and knocked out of position on the frame. Start by double-checking that the wheel is centered in the frame because you don’t want to ruin the brake adjustment if it’s actually set correctly.

To center sidepull brakes (road bikes), loosen the attaching bolt behind the fork crown or brake bridge until the brake is loose. (It should move sideways when you push it).

Now, squeeze the lever to hold the brake pads against the rim while you tighten the brake bolt on the back of the frame. If the brake needs minor fine-tuning after this, look for a small screw (it might be an Allen type) on top of the brake. Clockwise turns (photo left) will move the brake shoe on the side of the screw away from the rim and vice versa. (This screw is not intended for major adjustments.)

If adjusting the screw doesn't center the brake, screw it back to where it was and double-check how well centered the wheel is because that's probably the problem.

To center linear-pull brakes (off-road and hybrid bikes), look for a small screw in the side of the brake arm. Clockwise turns of this screw (photo right) will move the pad in the arm with the screw away from the rim and vice versa.

Brake BindingBrakes should operate smoothly and easily and the brake pads should snap away from the rims when you release the levers. If not, the brake pivots or cables might be dry, causing binding. To free the pivots, lightly lubricate the brakes where the arms pivot (photo below) and squeeze the levers repeatedly to work the lube into the brakes. (Be sure NOT to get any lube on the brake pads or rim. If some gets on them; wipe them clean with rubbing alcohol.)

Better? If not, it might be the cable that needs lube. Usually, this is only required on rear cables with split housing (if you have split housing you can see the middle of the inner cable and the housing is in two pieces).

Look closely at where the housing sections enter the stops on the frame. If the stops are split, you’ll be able to remove the housing and lubricate most of the cable. If the housing stops aren't split, raise the bike so that gravity will draw the lube into the housing section, apply a few drops of lube on the cable and squeeze the rear brake lever to draw the lube into the housing. Repeat for the front section of housing.

If the housing stops are split, open the quick release on sidepull brakes or unhook the noodle on linear-pulls. This should provide enough slack so that you can pull gently on the housing sections and free them from the frame stops (photo). If you need more slack, squeeze the brake shut with your hand.

When the housing is released from the stop, slide the rear housing section (with flat-handlebar-equipped bikes you’ll be able to slide the front housing section, too) along the cable so that you can lubricate the cable where it runs inside the housing, which should eliminate the binding. Then reconnect the cables and your brakes should feel as good as new.

BICYCLE REPAIR

Page 13: Bicycle Brake Adjustments

 

Brake pads (sometimes called “brake shoes”) are what rub against your rims to provide stopping power when you squeeze the brakes. This rubbing action means that the pads require occasional maintenance to function optimally. And also, that the pads will wear out after a while and need to be replaced. Here are our guidelines for keeping your brake pads in tip-top shape.

Click here to learn more bicycle brake adjustments.

Please note: These instructions are for conventional brakes, not disc brakes. Also, because brakes are so important for safety, do not work on them unless you’re confident in your ability to do the job right. And, keep in mind that in order for brakes to work properly and to make the adjustments explained in this article, the wheels must be true and round (no side-to-side wobbles, up-and-down hops or bends).

Keep the pads clean and free of debrisFor optimum braking, the rims and brake pads must be clean. As you use your brakes, however, the pads strike the rims picking up anything on them and sometimes transferring rubber deposits to the rims. The pads even pick up bits of sand and gravel that then grind the sides of the rims as you brake wearing them prematurely. This is another reason it’s important to keep the pads and rims clean (rim replacement is expensive).

To clean them, dampen a corner of a rag with rubbing alcohol and scrub the rims to remove any rubber deposits or grimy build up. Then wipe the surfaces of the brake pads to clean them.

Also, look closely at the faces of the pads (this is easiest if you remove the wheel). Sometimes you’ll find embedded shards of aluminum from the rims. Or, you might find small pieces of sand or stone left over from your last muddy mountain-bike ride. Pick any debris out with a pointed instrument (photo), such as an awl. This will improve braking and save your rims.

Replacing brake padsHow often you need to replace brake pads depends on where and how you ride. The important thing is that you understand how to check your pads so that you don’t end up without brakes when you need them.

Brake pads wear down a little every time you apply the brakes and you feel the change at the levers. As the pads wear, you have to pull the levers further before the brakes start to grab.

When the pads are really worn, you’ll squeeze the levers hard and the pads won’t grip the way they once did. This is a sign that it’s time for new pads to restore your braking. Don’t put off this important maintenance because when the pads wear down all the way, you’ll have no braking power, which is dangerous. In some cases, when the pad is worn out, the metal pad holder contacts the rim and

Page 14: Bicycle Brake Adjustments

it will only skid along the slick surface of the rim providing little grip and no braking power.

It’s a good idea to check your pads visually before rides, too. New brake pads have grooves in them (photo). These channel water away from the rims to improve wet-weather braking. They’re also a convenient way to gauge pad wear. When the grooves are almost worn away, it’s time for new pads.

Pad typesThere are two types of brake pads, cartridge and bolt-on. The former is much easier to replace because it simply slips into the holder and you’re good to go. Bolt-on pads must be aligned during installation, which requires practice to get right.

If you have cartridge pads, there’ll be an open end on the back of the pad holders (the metal piece the pad slips into; see photo). Sometimes, there’s a pin (linear-pull brakes) or an Allen bolt (sidepull brakes) that keeps the pad in place. To replace the pads, remove the pin (photo) or bolt, push out the bad pad, install the new one and reinstall the pin or bolt (if necessary).

Keep in mind that pads usually fit a certain way (photo). Look for markings or compare the new one to the old one to make sure it’s oriented correctly (it’s always best to replace one pad a time so you can compare the new one with the one still in place).

Pads might be tight, too. If you can’t push it out, try slipping a small screwdriver between the pad and its holder and prying to get it out. You should be able to push the new pad in with your fingers. If it’s a tight fit, make sure you’re putting it in the right way. You can also breathe on the pad to wet it slightly, which will make it slide in easier. Or, wet it with some of the rubbing alcohol. This won’t harm the pad and it will evaporate quickly.

Bolt-on pads are usually one piece with a bolt or post (photo). To replace these pads, loosen the bolt holding it in place (remove it if necessary), take out the old pad and insert a new one. Then, carefully align the pad so that it strikes the rim squarely when the brake is applied.

This usually means manipulating spacers and/or washers, which allow angling the pad to strike the rim properly. Sometimes these parts corrode slightly making it difficult to position them as needed. Free the parts by applying a little lube, which will make it easier to align the brake pad.

And, remember to only work on one pad at a time so you can match the position of the new pad to the one still in place on the other side of the brake (they should match).

Pad alignmentIn setting the new pads, your goal is to get them to strike the center of the rim when you apply the brakes (photo). This involves putting them at the right height and depth (for pads with posts) so that they contact the rim correctly. Ideally, the entire flat surface of the brake pad will contact the rim when you brake.

If you get the angle wrong, the contact patch will be reduced limiting your braking power. If the position is really wrong, the pad might rub on the tire ruining it and causing a flat or dive under the rim and into the spokes under hard braking. So, take your time and get it right.

Toe-inOne glitch that affects some brakes and can drive you bonkers (and guarantee that you never see any wildlife) is squeaking. To prevent this, there’s a brake pad adjustment called “toe-in.” It involves slightly angling the leading edges of the pads in to touch the rim first.

As pads wear, the toe-in wears away so you probably won’t notice this looking at your old pads. With cartridge pads, the toe-in will be there once you replace the pad. With bolt-on types, however, you’ll lose the setting when you install the new pad. So, you’ll have to set it during alignment.

To do this, angle the pads so that there’s about a .5mm gap at the backs of the pads when the front edges strike the rim (photo). Some mechanics slip a piece of cardboard under the rear of the pad to set the angle right.

Bicycles/Maintenance and Repair/Brakes/Adjusting Rim BrakesFrom Wikibooks, the open-content textbooks collection

Page 15: Bicycle Brake Adjustments

< Bicycles | Maintenance and Repair | BrakesJump to: navigation, search

Bicycles

Contents

[hide] 1 ADJUSTING RIM

BRAKES o 1.1

Preliminarieso 1.2 Method

Summaryo 1.3 Brake Block

Alignmento 1.4 Block

Clearance 1.4.1

Rough Adjustment

1.4.2 Fine Adjustment

o 1.5 Brake Block Balance

o 1.6 Final Check o 1.7 Common

Brake Problems 1.7.1

Balance Problems

1.7.2 Soft Brakes

o 1.8 Changing Cables

o 1.9 See Also

o 1.10 External Links

Fig 1. Typical Bicycle Brake Details

ADJUSTING RIM BRAKES

The brakes on bicycles are simple to adjust. They are an essential piece of safety equipment, so learning to adjust them is a worthwhile skill. Remember, after adjusting brakes; try them in a safe environment before riding.

Most bicycle brakes use a lever on the handlebars to pull a cable. On ordinary rim brakes the cable pulls on brake arms, and brake blocks (also known as pads or shoes) press against the metal rim of the wheel. Friction then slows the bike.

Bear in mind that the best way to learn the adjustment of brakes is to be shown by somebody while it is being done; in this way much of the mystery vanishes.

The next best way is to follow a fairly stolid description of the sort below, which will get the job done with a little perseverance.

Preliminaries

Consider these few things before carrying out brake adjustments:

Page 16: Bicycle Brake Adjustments

Inflate the tires first. Before adjusting the brakes, make sure that the tires are properly inflated, since flat tires will affect the results. Believe it or not, metal rims can move as tire pressures change.

Is a full adjustment really needed? Before doing any elaborate brake adjustments it is a good idea to decide whether or not a simple barrel adjustment might fix it. If you think that this is so, refer to Fine Adjustments below.

Preset the barrel adjusters. Before doing elaborate work on the brakes, first set the barrel adjusters, (Fig 1), so that they are out by two full turns, instead of being all the way in. This allows some fine adjustment in both directions at any stage, and allows the cable to be slackened to release the brake blocks when necessary.

Check that the rims are clean. Remove any dirt and oil from the rims, and if necessary clean them with detergent and wire wool, being careful to avoid the rubber of the tires.

Make sure that the wheels are correctly set. The wheels should be fully engaged in the dropouts and centered in the wheel arches if brake balancing is to work.

Check the brake blocks for wear. Make sure that the brake block contact areas have not been badly reduced. If the surface grooves on the blocks have been removed by wear, then the blocks should be replaced. If replacing them then be sure to replace both at the same time.

Method Summary

The details of typical rim brakes can be seen in Figures 1, 2, and 4, and a summary of the expected braking distances can be found in Figure 3. The general method for each set of brakes is as shown below, though it is quite usual to repeat balancing at various stages throughout the adjustment.

Position each brake block so that it presses cleanly onto its wheel rim.

Set the brake cable length to roughly establish the brake blocks' clearance.

Adjust the brake-arm balance screws so that both blocks close onto the rims together.

Fine-adjust the handlebar barrel-adjuster for the required brake performance.

Test the brakes both off and on the road.

These above points are all described in some detail in the text that follows.

[edit] Brake Block Alignment

Page 17: Bicycle Brake Adjustments

Fig 2. Block Alignment. Note the direction of 'toeing-in'.The brake blocks need to be aligned with the metal rims. Refer to Figs 1 and 2. The leading edge of each block should be slightly closer to the rim than its trailing edge. This prevents brake squealing and is called "toeing-in". Use a coin, a credit card, or any other thin material under the back end of the block while adjusting it. Some suggest tying an elastic band temporarily to the trailing end of the block to allow more freedom while working.

To make the adjustment, slacken the screw that holds the block. Usually a 5mm hex wrench is used. Swing the brake arm in so that the block is pressed squarely against the metal rim, and then re-tighten it while holding the block hard with your "toeing-in" device in place. Avoid the rubber of the wheel; the block should contact only the rim. The block should be parallel to the rim, noting that some blocks are curved to fit its shape. Do one block at a time, and just let each arm relax after the block is set. If there is insufficient clearance to work or if you intend adjusting the cable length later in any case, then unhook the cable bridge or undo the cable clamp before carrying out the work.

[edit] Block Clearance

Decide whether or not the block clearance is correct by trying the feel of the brake lever . The brake should feel responsive without too much handbrake slack prior to the start of braking. Some mountain bike V-brakes might need only a 1mm gap, while many other brakes need about 2mm. If in doubt, refer to your bicycle handbook. If a significant adjustment is needed, resetting the cable length should do it. If a small change will do then use the brake lever barrel-adjusters on the handlebars, as described in the Fine Adjustments below.

[edit] Rough Adjustment To reset the cable length slacken the brake cable clamp, (usually with a 5mm hex wrench.),

and let the brake side arms relax. Move both of the side arms toward the rims until the blocks are about the right distance away; although you can do this in any way that you like, it is easiest to hold one arm against its rim and adjust the other's gap so that it is about double the intended block clearance. Pull up any cable slack and re-tighten the cable clamp. This may take a couple of tries to get the blocks close to, but not touching, the rim. In any case, fine adjustments can be made with the barrel adjusters, provided not too much range is expected of them.

Page 18: Bicycle Brake Adjustments

In the absence of documentation about the brakes, aim for the combined clearance of the two blocks on v-brakes to be about 2mm; this will give 1mm gaps after balancing. For less demanding brakes, assume about double this figure. Some manufacturers provide internet sites with technical information of this kind. A good example of a manufacturer's brake manual can be found in pdf format here, and its parts list here.

[edit] Fine AdjustmentFine adjustments are made with the handbrakes' barrel-adjusters. (Fig 1). If not on the handlebars they may be near the brake blocks. If the brakes just need a small adjustment, this may be all that you need.

Barrel adjustment; after undoing the barrel-adjuster's locknut the brake blocks can be moved by turning the barrel screw. To move both brake blocks inward, simply unscrew the barrel (counter clockwise). Conversely, to move both brake blocks outward, turn the barrel inward, (clockwise). This feature gives a much finer adjustment of cable length than setting the cable clamp. Check the feeling of the brake frequently while getting the adjustment right, and tighten the locknut again when it is done. Lastly, decide whether or not to re-balance the brake arms.

Notes on barrel range: There are differences of opinion as to the ideal amount of thread to leave on the adjusters when the brake adjustments are complete. The main ideas are these:

o For maximum barrel range; screw the barrel adjusters all the way in before making any brake adjustments to allow the widest range of inward adjustment of the blocks. This might be the case where compensating for block wear is the main consideration.

o To unhook the brakes; for example, when a wheel is being removed, there is no need to slacken the cable clamp. If there is enough adjustment range on the barrel-adjuster, it can be tightened to slacken the cable as much as possible, before unhooking the cable nipple from the slot in the cable bridge (see Fig.1). Some choose to do things this way; decide which is best for your routine.

[edit] Brake Block Balance

'The brake arms should be adjusted so that both blocks apply pressure to the rim at the same time . As a result, at balance, there is no sideways displacement of the wheel during braking. Although slight imbalance is not always critical, displacement of the wheel by even a small amount can cause damage when small-clearance devices such as distance counters are installed on the spokes. Balancing the spring tensions keeps the wheel centered even during braking.

For brakes like V-brakes, there is a small screw near the bottom of each brake arm to adjust the spring tension.( Fig 4). It is often a posidrive screw, (M4x6mm) , with a thread tightening compound. Turning this screw clockwise will cause the brake block to move outward slightly, and turning it anticlockwise will cause the block to move inward. As one block moves, so does the other, to maintain the distance between them. Adjust these until the clearances are about equal. In this way, operating the brake causes the blocks to reach the rim at about the same time.

Be careful not to withdraw the screws too far since they are not captive. At the other extreme, if the screws are too far in, they commonly bind the brake arms; if a brake arm seems inactive, or unresponsive, this might be the case, or the spring may just have popped out of its slot. Try to avoid the limits and to reach a balance with the screws near their mid-range. This is easier than it sounds since making an identical adjustment on both screws will leave the balance unchanged.

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For side-pull and centre-pull brakes, slacken the central retaining bolt and correct the position of the whole brake assembly.

[edit] Final Check

Fig 3. Maximum Braking Distances for Adult-Sized Bicycles. These figures can be found in CTC Standard for the Safety of Hired and Used Cycles, ( 5/3/99 ).

Maximum Braking Distance (metres)Dry Flat Surface

Wet Flat Surface

Remarks

Speed 24 kmph (15 mph) using both brakes 5.5 m n/a Only if safe

Speed 24 kmph (15 mph) rear brake only 14 m n/a Only if safe

Speed 16 kmph (10 mph) using both brakes 2.5 m 7.5 m Safest to Test

Speed 16 kmph (10 mph) rear brake only 7.5 m 19 m Only if safe

Rotate the wheel to check brake clearance. Make sure that there are no repetitive noises coming from the brakes.

Test the brakes on the spinning wheels before riding. If these work well enough then test the brakes again by riding the bicycle in a quiet place. The brakes should stop the bicycle decisively in a fairly short distance. Some v-brakes in particular have a short stopping distance; on these you should not need a deep pull on the brake lever for a good braking effect since this is a sign that the blocks are set too far from the rims. In any case be sure to refer to the manual if there is doubt.

Figure 3 is an extract of maximum braking distances as given by the CTC Hire Standard, that is itself related to the content of British Standard BS6102/1 for new bikes. The CTC standard is an attempt to consider used bikes, as opposed to bikes at the point of first sale. In any case, these stopping distances are useful until such time as the European standards properly address the issue.

The most common reason for long braking distances, apart from maladjusted brakes, is the degradation of the brake block surface area. Be sure if replacing these to replace both together.

[edit] Common Brake Problems

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[edit] Balance Problems

Fig 4. Typical Brake Layout. Note the location of the balance screws.Sometimes, despite best efforts, the brake arms will not balance. The spring balance screws are designed to have limited range since they are only expected to handle the difference between the arm tensions to achieve balance. So, faults that only slightly bind any part of the braking system can cause trouble with balancing. Possible faults include: The lack of general lubrication, the binding of brake arms, the slipping of faulty adjustment screws, unseated brake-arm springs, unseated cable nipples, or a quick-release wheel that needs reclamped closer to the centre of the wheel arch. See these points below.

Fig 5. Typical Brake Block Assembly. Note the washer padding for a persistent balance problem.LubricationSmall changes in brake arm resistance are often corrected by lubrication alone. As a last resort, to identify the source of binding, undo the cables at the brake levers, and at the cable clamp; this can isolate the three parts of the system. In this way, each section could be studied without being affected by the other parts. Any roughness in operation could then be observed. Many problems of this kind however, are solved by routine cable lubrication.

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The moving parts of brake assemblies, with the exception of blocks and rims, should be oiled. Use a light machine oil of the type sold for bicycles. Brake lever assemblies, cables, and the brake arms should all be lubricated. Cables are oiled by first undoing the cable clamp, then with the cable loose, dripping a drop of oil into points where cables enter sheaths or fixings. The brake lever cable connection on the handlebars is accessed by lining up the two slots in the barrel adjuster then sliding the cable through the slots. A singe drop of oil at the point where a cable enters a sheath will travel the length of the cable by capillary action. Rub some oil also onto any other visible steel cables. If necessary, consider removing the brake arms to lubricate the mounting pins.Balance ScrewsThe balance screws work by pushing and releasing the coiled ends of the springs, increasing and decreasing their strength. However, things sometimes go wrong.In some brakes the brake arm binds up when the screw is all the way in. In others, the screw slips off the end of its spring because of bent parts or poor design. When either of these things happens it will be difficult or impossible to balance the brakes.If the balance screws seem to lack range of adjustment. then look for these problems on the underside of the brake arms. In the case of binding screws it is simple to release the screw a bit and reattempt the balance. Bear in mind that carrying out an identical adjustment on both balance screws should leave the balance unchanged, so unless there is some other problem, it will usually be possible to correct binding in this way. A better fix for a binding screw is to add a few thin washers under the balance screw head to avoid binding in the future. This limit should be set to avoid the worst case; found usually with the block against the rim. If the screws are ever replaced, avoid using screws that are longer, unless the extra is padded out ,as mentioned above. This will avoid brake binding. Remember to use some PTFE tape or other tightening compound on the screws to avoid their getting lost on the road.Sometimes the spring on a brake arm slips out of its groove, and this is seen as one side of the brakes doing nothing at all. This happens at times when the bridge has been undone. Fix it by moving the spring back behind the arm into its groove. At other times, the springs of cheaper brakes can slip off the balance screws, but this is largely a fabrication problem; consider a new set of brakes if this happens, since these springs are not easily reworked.Brake arms have location pins to fix them to the flats on the bike frame. The frame often has three holes to choose from but some frame mountings have only one. The hole chosen decides the spring's strength and the work needed to pull the brake lever. If the pins of each brake arm in a set are located in different positions, then the resulting tensions cannot be balanced. If there is an obvious imbalance in the brake arms and the arms were recently reassembled, then consider this possibility.Obstructed CablesIt has been noted that accessories such as straps, lock cables, and bungee cords are easily forgotten, and can bear upon brake cables in such a way as to make the balance seem impossible. The same condition is possible when the metal parts at the ends of cable housings become unseated during brake work; the entire brake balance suffers. Baggage on the front handlebars can kink a brake cable at the point where it enters the cable bridge, especially if the cable-guide is is of the spring type and not solid; if this is the case it can be improved with a plastic tie on the cable-bridge to give it a more direct entry, or by using a more solid guide-piece. If the change is fairly sudden, and in particular after parking the bike or unhooking the cable bridge, then look for these simple solutions.Wheel not CenteredMany brake balance problems are associated with wheel positioning. There are at least three situations to consider:

When a quick-release wheel is positioned within the wheel arch it can happen that it is not fully engaged in the dropouts. This happens when a wheel is installed with the bike in a stand or otherwise above ground. A gap is often visible. This problem causes the brake blocks to close on the rubber of the wheels instead of the rims, so it is not subtle. Reset the wheel.

Brakes are adjusted for the quick release lever positioned on the left of the bike. When a front wheel is wrongly installed with the clamp on the right, the existing brake balance will be upset. Reinstall the wheel with the lever on the left.

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When a wheel is installed it is important to make sure that the wheel is centered in the wheel arch. This problem also causes the bike to run poorly and it might feel a bit heavy. The two springs, one on each end of the skewer, (both with their pointed ends inwards) are there to better center it. The springs are not strictly necessary for the skewer to work, and as such they might be missing. In any case a wheel can be centered by adjusting both the lever and the locknut. One way to do this is to slacken both ends until the exposed screw threads look about equal, then tighten both the locknut and the lever a little bit at a time. Make final adjustments in the same way until resistance is first noted when the closing of the lever approaches the horizontal. Some tires have a center ridge that is useful for checking that the wheel is centered. When this problem is corrected the adjustments will come into range, and the bike might even run better.

All Else FailsIf the brakes balance, but at opposite screw extremes, then further adjustments are prevented. First consider all of the above solutions; i.e., is the tighter of the two binding, etc.? If you are stuck with unmatched springs in the brake arms, (rare, since the set that came with the bike are matched in manufacture), it may be possible to get the screws back into mid-range with a washer or two. Add thin 6mm washers, as shown in Figure 5, to the brake block assembly that habitually has the wider of the two gaps. Adjust the number of washers until the balance is achieved closer to the balance screws' midpoints.When all else has failed, and a fix of this kind is being considered, do not forget to consider the buying of a new set of brakes, and getting the bike shop to first take a look.

[edit] Soft Brakes

If brakes are softer than intended, even after adjustment, then it might be that the toeing-in is excessive. Also, if wheel wobble causes rubbing on the brake blocks, widening the gaps will necessarily soften the brakes. See the comments below.

Excessive Toeing-inIt is impossible to set firm brakes if the blocks cannot be set close to the rims. For brakes needing narrow' clearances, e.g. 1mm to 1.5mm, the toeing-in needs also to be narrower than usual. If the toeing-in were set to the usual 1mm more than the front of the block, then for the above example, the average clearance for each block would be 1.5mm to 2mm, and the brake would feel soft. Thus, the toeing-in needs to be minimal if a firm or hard brake is required. In fact some brake manufacturers recommend no toeing-in for their products. Brakes that use wider settings by design, are affected less by toeing-in.Wheel WobbleWheel wobble causes repetitive brake noise but most brake noises are unimportant. The most common cause is debris from the road. Also, new tires have rubber tails on them that rub on brake blocks, but these can be trimmed. Faulty wheel locking with a quick release can also cause some rubbing of the brakes. It is as well to check this if the problem follows recent wheel work. These noises are not serious.If there is even a slight wheel wobble then brake block clearances will need to be widened to avoid the repetitive rubbing noise. Although some wheel wobble is inevitable, when it is excessive then repairs may be required. In that case see: Truing a bicycle wheel , in an attempt to handle it yourself, or consider getting some advice from your bike shop.For brakes that need narrow clearances, say 1mm, the issue of wheel balance is more critical. Widening the block clearances to 2mm, to accommodate a slight wobble makes softer brakes, but in most cases these will still be safe. However, if the wobble worsens, then continuing to widen the clearances will lead to ineffective brakes long before the wheel itself becomes unusable. Brakes designed for wider clearances will accommodate more wobble before the brakes suffer.

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[edit] Changing Cables

A brake cable is a braided steel wire with a small locating part at one end. This part is called a nipple. The nipple fits into a slot within the brake lever, and when the lever is pulled, the cable is pulled to operate the brake arms. The barrel adjuster pushes the part holding the nipple back or forward to fine adjust its starting position. The shape of these fittings is different for racing bikes and other bikes.

Drop-handlebar ("racing") brake levers have a pear nipple and straight handlebar levers have a barrel nipple. Universal cables are available that can be used for any bike. They have a different nipple at each end. When the cable is cut to length the unused nipple is discarded.

Brake cables run through a protective shroud called an outer or cable housing for part or all of their length. The section leading from the handlebar to the frame is always surrounded by an outer. Together, the cable and outer form a bowden cable.

On racing bicycles and some others, the cable is open where it runs along the frame. In these cases small pulleys are used where the open cable changes direction.

To remove an old cable, slacken the cable clamp bolt where the cable is fixed to the wheel's brake arm. Then the cable can be pulled through the various outer sheaths until it is at the barrel adjuster on the handlebars. The cable is removed from the handlebar barrel adjuster by first lining up its two slots. Then the cable nipple can be unhooked from the brake lever by sliding the cable through the slots. Old steel cables can be recycled.

To install the new cable, put a little grease on the nipple and locate it in the lever. Then feed the other end of the cable through any cable outers, adding a little grease. Dress the cable through any pulleys, stops and guides until it reaches the brake arm assembly. Feed the end through the brake arm clamp bolt.

It may be necessary to cut the cable to length, and the exact length is best taken by measuring the old cable. Cutting these cables is almost impossible using ordinary electrical tools, and a special cutter exists for the task. Be sure to leave at least 10 or 12cm or so of spare cable when cutting. Crimp a cable termination onto the cut end, preferably before feeding the cable, to prevent fraying, and eventually to act as a stop during the slackening of the cable clamp. Some individuals have been known to solder the cable end.

Bear in mind that a new brake cable will stretch with use, and you will need to take up slack with the brake adjustments after the first hundred miles or so.

Direct-Pull Cantilever Brake Adjustments

Bicycle brake pad misaligned - Realign a rear or front direct-pull cantilever brake pad if it is rubbing against a tire, hitting spokes, or not effectively gripping the bicycle tire rim (e.g., making a squealing sound). First, use an Allen wrench to loosen the bolt attached to the back of the brake pad (see first picture below). Second, engage the brake pad with the tire rim by squeezing the brakes. Third, align the brake pad such that it is centered on the tire rim and that the entire brake pad is making uniform contact with the tire rim. Fourth, tighten the bolt attached to the back of the brake pad maintaining desired alignment. Finally, test that your brakes are now working to your liking and that they are not rubbing against your tires, hitting spokes, or making a squealing sound.

Bicycle brake pad does not separate from tire rim - If a rear or front direct-pull cantilever brake pad does not retract away from a tire rim after releasing the brakes then the problem may be with the tension in the brake

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arm's spring. Tighten the tension in the brake arm by turning the tension screw clockwise with a Phillips screwdriver. Reduce tension by turning the screw counter-clockwise. The tension screw can be seen in the following picture as the small black screw at the base of the brake arm. In addition, it is recommended to clean the brake arm with WD-40 so that the brake arm can move freely.

Bicycle brakes are too loose or too tight - Front and rear direct-pull cantilever brakes can be loosened or tightened by adjusting the length of the brake cable. First, use an Allen wrench to unwind the bolt that pinches the brake cable. For loose brakes, shorten the length of the brake cable. For tight brakes, lengthen the brake cable. Next, tighten the bolt with your Allen wrench. Finally, test that your brakes are now working to your liking. It should be noted that front brakes provide most of your stopping power but you do not want to overuse them at high speeds such that your front tire locks up and sends you flying over your handlebars.

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Figure 4 - A standard bicycle brake lever

Practically every type of bicycle brake will require a cable and some type of lever to activate it. The lever pulls the braided steel cable through the outer housing, transferring energy to the brake system. Most levers can move the inner cable about 1 inch, which is plenty of distance to allow for light braking all the way up to a full wheel lockup. A typical brake lever is shown in Figure 4, having a steel lever and a hard plastic body that can clamp to a handlebar. There are hundreds of styles of brake levers, but essentially they all do the same job - pulling a cable an inch or so.

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Figure 5 - Brake lever adjustment points

Bicycle brakes allow for several adjustments that will change the level of braking power, speed of braking power, and cable tension. The easiest way to “fine tune” a bicycle brake is by adjusting the hollow bolt at the brake lever as shown in Figure 5. The bolt allows the brake to be compensated for pad wear without having to adjust the brake end of the cable or pads by simply altering the length that the outer cable shield is away from the entry point on the lever. If your brake pads are worn a bit, unscrewing this hollow adjuster bolt will “pick up” the slack. Figure 5 shows this bolt after unscrewing it about ¼ inch and then securing it with the locking nut (marked B).

The other lever adjustment (Shown as A) allows the lever return spring tension to be changed. Not all levers offer this adjustment. If a brake seems to rub after it has been engaged, the return spring may need to be tightened a bit, although this could also indicate a bad or rusted cable.

Figure 6 - Adjusting a cantilever brake

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Cantilever style caliper brakes also offer a few points of adjustment as shown in Figure 6. The screw shown as (B) is another return spring adjuster that will help move the pads off the rim if the cables are a bit sticky. There is one screw on each side of the brake, as the adjustment may only be needed on one side. The point marked (A) is the bolt that locks the brake pad to the braking arm and it needs to be adjusted so that the brake pad contacts the rim perfectly as shown in Figure 6 when fully engaged. If the pad is not aligned properly, it will either offer poor braking or destroy the side wall of your tire.

Figure 7 - Side pull brake adjustment points

Side pull caliper brakes have a similar adjustment system as shown in Figure 7. At point (A), the brake pad is set up so that it makes perfect rim contact when fully engaged. At point (B), the hollow bolt allows the cable to be adjusted for brake pad wear by moving the bolt and then locking down the small lock nut. In extreme cases, it may be necessary to loosen the cable clamping bolt at point (C) to adjust the actual cable. Pads should lift completely away from the rim edge when not in use, yet have enough power to lock up a rim when fully engaged. Brake quality, cable length and rim type have a lot to do with optimal braking performance as well.

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Figure 8 - Adjustment points on a disc brake

A disc brake system also has a similar set of adjustments that can be made, such as cable adjustment (point A) and pad distance (Point B). By turning the small red dial, the pads are set closer to or further away from the rim to allow for responsiveness, as well as pad wear. Unlike pad brakes, a small bit of rubbing is usually okay in a disc brake as some hardware is designed to let the pads “rest” very close to the rotor surface. A disc brake should not have any resistance when not engaged, nor should it make an annoying ring, so the pad adjuster needs to be set correctly.

Figure 9 - Removing a brake pad

Brake pads are wear parts, and need replacing when they are spent. Although I have yet to see a disc brake wear out, I have seen many rubber pad brakes worn enough to replace. As shown in Figure 9, a caliper brake pad is removed (and adjusted) by unscrewing the nut or bolt that secures the bad to the braking arm.

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Figure 10 - Brake pad completely removed

On a cantilever brake system, the brake pad has a stem that seats into a cup that acts like a vice, allowing the pad to be moved in several degrees of freedom in order to adjust to the rim. A side pull brake is similar, although it only allows the pad to adjust up, down, and rotated around for rim adjustment. Many pads are interchangeable between brakes of the same type, so it is easy to swap parts if you have been collecting them.

Figure 11 - Cantilever brake studs

Cantilever brakes require a pair of studs that are welded to the frame in the proper place to allow the pads to contact the rim. These small studs can be easily cut from a frame or front fork by using a zip disc or hacksaw

and then transplanted to a new frame by welding them in place. Figure 11 shows a pair of cantilever studs after removing them from the seat stays of an old bicycle frame.

ck to list | print-friendly version   SIDEPULL BRAKE SERVICE

Useful Tools and Supplies

Repair Stand , holds bike secure for easy work.

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Hex wrenches Light liquid lubricant Bench vise with soft jaws, such as the AV-1 Brake wrenches such as OBW and CBW Metric wrenches, 13mm and 10mm commonly required

Properly adjusted brake systems require attention to small details. This article will discuss sidepull caliper arm adjustment, pad adjustment to the rim, pad centering, and pad clearance. For purposes of this article, the terms "left" and "right" will be from the "mechanic's point of view", not from sitting on the bike.

See also related articles:

Cable Housing Length Shift Lever and Cable Attachment Dual Pivot Caliper Brakes Linear Pull and Shimano® V-brake Calipers Cantilever Caliper Brakes

The side pull caliper rim brakes were once the common road bike brake. Both caliper arms share a single pivot, which is centered over the wheel. The image above shows modern dual pivot, and centerpull brake calipers, and sidepull. Sidepull calipers are also found on some BMX, Freestyle, and some recreational bikes.

Both brake pads move downward on an arc as they approach the rim. As the pads wear thinner, they will travel downward even more. Generally for side pull, adjust pads to the top of the rim braking surface, but not so high they would strike the tire. See image below.

Pad and Caliper adjustment

1. Inspect the wheel for adequate centering in the frame/fork. Correct as necessary.2. Loosen and lubricate threads of pad fixing bolt/nut. Adjust pads so they strike strike upper edge of

braking surface, but not the tire.

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3. Check front end and back end of pad. The pad should be square or tangent rim.

4. Tighten pad-fixing bolts.5. Attach cable (if necessary). Squeeze lever to test pad clearance. Use barrel adjuster to adjust pad

clearance. Set clearance as desired. Draw slack from system using inner-wire pinch bolt if barrel adjuster is set out to its limit.

6. View pad centering to rim. If pads are off-center, manipulate center pivot bolt. There are different procedures possible.

Some models use a flat machined into the center stud. Use the Park Tool OBW Offset Brake Tool or a cone wrench to grab this flat. Place a wrench on the mounting nut behind the brake. Move both wrenches the same direction and same amount to move the pivot. In the image below the wrenches are rotated counter-clockwise from our view, which moves the caliper arms counter-clockwise arond the pivot bolt.

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Saftey pivot types have the pivot bolt head in front of the caliper arms. Use a wrench on the mounting nut and a wrench on the bolt head. DO NOT use the nuts behind the calipers arms as centering flats.

If the brake is a double nut type, and has no centering flat, it may accept the OBW-3 spanner. Use the OBW-3 to grab the spring and move the pivot. It may also be necessary to loosen mounting bolt and move brake to center, hold it by hand and re-secure mounting nut.

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NOTE: It is not critical or even important that brake pads strike the rim at the same time. It is possible for one pad to reach the rim first. The rim will not be pushed to the side because the pivot of the brake arms is above the wheel. The other pad will eventually strike the rim and the pads will then squeeze the braking surface to slow the bike.

Squealing is the result of a harmonic resonance from a slip-and-stick phenomenon, similar to how a violin bow resonates on a string. The brake pads grab the rim and are pulled forward by the force of the wheel. The arms must at sometimes jerk backwards, but if you are still braking, the arms are flexed forward again. This is repeated again and again many times per second, and this creates the squeal. Because of this, flexible and less expensive arms tend to squeal more than stiff calipers of better brakes. It is possible to reduce squeal by having the leading edge of the brake pad strike first. This tends to reduce the back and forth jerking of the arms.

Some brake caliper arms can be toed. Toeing can be achieved in some cases by bending the caliper arm slightly using the Park Tool BT-3. It is best to use two BT-3 tools at the same time. This will minimize stress on the center pivot. Begin with a slight gap at the back of the pads and test the bike before adding toe. An option to toeing is to file the pads so the leading edge strikes first.

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Pads will wear out with use and require replacement. Pads will also harden and become ineffective with age. Pads may also become embedded with aluminum or other contaminants. Inspect and remove as necessary. Pads that are aligned too low on a rim will tend to develop a lip on the low edge. This lip makes correct alignment impossible.

Sidepull Caliper Arm Adjustment

The caliper arms pivot off the center bolt or stud. The arms should open fully when squeezed, but should have no play or knocking. There are two basic types of sidepull caliper designs. The double nut type has two nuts in front of the caliper arms. The inner nut is the adjustment nut and is locked in place by the outer locknut. The other design type was commonly used by Shimano® and is called the "safety pivot". In this design, there the adjusting nut and locknut are behind the brake arms. The brake must be completely removed from the bike to have the caliper arm movement adjusted. The adjusting nut doubles as a the spring holding nut.

Double Nut Adjustments

The double nut types can be adjusted with the caliper mounted to the bike. Check arms for play by grabbing each arm and moving back and forth along the axis of the pivot. If there is no play and the calipers open when gently squeezed, the pivot adjustment is adequate.

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If there is play, the adjustment should be tightened. Hold the adjusting nut secure with a thin wrench, such as the CBW or OBW wrench. Note position of wrench. Loosen locknut with a second wrench, and move adjusting nut slightly clockwise. Hold adjusting nut and secure locknut fully.

Repeat check of caliper arms for play. Repeat as necessary until play is gone and brake open upon gentle squeezing. If arms will not fully open when gently squeezed, the adjustment may be too tight. Try to adjust looser a very slight amount. With much use the spring may become fatigued and a good setting is not possible. Replace spring if necessary.

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Saftey Pivot Type

Safety pivot caliper arm mount to a single bolt. Below the caliper arms shown apart on the pivot bolt.

The locknut and adjusting nuts for the safety-pivot types is located behind the caliper arms. The brake must be removed from the bike to access these nuts. The spring must also be disengaged and flipped back out of the way. Use care not to damage plastic spring carriers, if any.

It is easiest to work with the brake in a vise using soft jaws such as the AV-3. If the brake has a 12-point locknut, place the box end of a wrench over the nut, and then grab with the vise. The adjusting nut also holds

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the spring, which can make the adjustment awkward. Hold the adjusting nut with a thin wrench such as the OBW wrench, and loosen the locknut.

Tighten adjusting nut, turning it toward bolt head, only slightly. Hold adjusting nut and secure locknut fully. Test for play, and repeat adjustment if play if felt.

To test final adjustment, flip spring back into place and attach spring to arms. Squeeze gently and release. Re-adjust as necessary.