manual transmission and transaxle service walla walla community college automotive technology
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Lubricant
Lubricants fulfill these requirements:Lubrication of the gears
Reduction of friction and power loss
Protection against rust and corrosionCooling Bearings and Gears
Carrying away metal particles
Reduction of noise from gear box
Lubricant Types
Refined or synthetic oils
Chemical additive are added with base oil to produce extreme pressure (EP) lubricant.
High Viscosity (thickness)
SAE 75W to SAE 140
Multi-viscosity oil such as: 75W-90
Some use Synchromesh Transmission Fluid (STF)
Other specify Auto Trans Fluid (ATF)
Lubricant InspectionCheck at recommended intervals7500 to 30,000 milesSome manufacturers recommend fluid life of transmissionSome units have dip sticksSome use fill plugClean area around plug before checkLubricant Level must not be more than ½” below fill hole
Lubricant ReplacementDrive vehicle to warm fluid
Drain lubricantInspect fluid for metal particlesReplace fill plug washerTighten plug to specified torque
Some drain plugs are magnetizedInspect for metal chips, bronze chips, etc.
Diagnosing Problems
Service Manuals
Must locate exact source of problem
Some problems seem trans related but are caused by other area of the car
Verify customer concern – Always road test with customer if possible
Don’t guess at diagnosis with customer
Visual Inspection of Case
Check lubricant
Check gaskets and seals
Check case for porosity
Inspect mounts dynamically
Move clutch and shift linkages
Transaxle boots
CV Joints
Seals and Gaskets
Inspect for wear at the lip
Loss of flexibility
Shaft Oil SealsCan wear a groove in shaft
Extension housing seal
Good to just replace during service
Speedometer Drive Gear
Inspect for worn or stripped teeth
Inspect gear shaft o-rings
Gears are color coded for application
Shafts Inspect inside bearing races of main shaft and countershaft.
Some have needle bearings or bronze bushings
Shaft spline wear, Inspect for shoulders worn
Pilot Bushing wear
Output Shaft wear, especially the front
Gear Condition
Inspect wear marks on gear teeth facesPolished surfaces are normal
Chipped, cracked or broken teeth means replace
Gear Tooth Inspection
Shiny Surface in center of tooth
Minor imperfections acceptable
Coast side wear less important
Can file imperfections sometimes
Bearings and Thrust WashersBall Bearings must rotate smoothly
Account for all bearingsSome are not caged
Thrust WashersMark them on disassembly
Measure for thickness and record
Check Specifications for thickness
Thrust Bearing
Inspect for wear
Roll bearing and check for smoothness
Inpsect roller bearings for pits, scoring, etc.
Inspect race for wear
Synchronizers
Synchronizers hubs and sleeves are matched setIndex parts before disassemblyInspect bronze synchronizers rings for wear
BreaksBroken TeethWorn groovesBroken or missing keysSlide sleeve back and forth and check for smoothness
Assembling The Transmission
Use Shop manual for correct procedureSequence
Use micrometer, dial indicator or feeler gauge for clearancesUse chassis grease to hold bearingsMultiple thickness thrust washersSelective fit snap ringsObserve Torque specifications carefully
Transmission Noise
Verify noise is coming from transmissionTest Drive with customerProcess of eliminationNoises
Bearings – Will show up worse under loadGear teethSynchronizers – Gear clashNoise specific to a certain gear
Rough Growling Noise
Several possible problems
Neutral with engine runningInput shaft roller bearings
Vehicle movingInput and output shaft rotating
If forward or reverse but not neutral, possible output shaft bearings
Rough Growling Noises
Engine Running, clutch engaged, trans in neutralFront input shaft bearing at fault
If moving in all gear range noiseFaulty counter gear bearings
If all gears except direct driveRear input shaft bearing
Clicking or Knocking Noise
Possible Helical gear broken teeth
Chipped or broken teeth my cause other problems
Gear Clash
Grinding noise during shifting
Caused by one gear set remaining partly engaged while another gear set attempts to turn the main shaft
Incorrect Clutch Adjustment
Damaged, worn synchronizers
Improper lubricant
Hard ShiftingDifficult to move from gear to gear (especially under
load)Check Clutch AdjustmentCheck hydraulic system operationDamage inside the transExcessive wear on gear locking or clutching teeth
gearBadly worn bearingsDamaged shift linkage
Jumping out of GearIf when decelerating
Shift lever and internal gearshift linkage wear or misalignment
Excessive clearance between gears and input shaftBadly worn bearingsInternal components
Clutch pilot bearingGear teethShift forksShift railsSprings or detents