TYPES OF FINAL DRIVE

FINAL DRIVE USED ON THE REAR WHEEL DRIVE

FINAL DRIVE USED ON THE FRONT WHEEL DRIIVE

OPERATION OF THE FINAL DRIVEFWD Final Drives

FWD final drives are very simple compared to RWD set-

ups. Almost all FWD engines are transverse mounted,

which means that rotational torque is created parallel to

the direction that the wheels must rotate. There is no

need to change/pivot the direction of rotation in the final

drive. The final drive pinion gear will sit on the end of

the output shaft. (multiple output shafts and pinion

gears are possible) The pinion gear(s) will mesh with

the final drive ring gear. In almost all cases the pinion

and ring gear will have helical cut teeth just like the rest

of the transmission/transaxle. The pinion gear will be

smaller and have a much lower tooth count than the

ring gear. This produces the final drive ratio. The ring

gear will drive the differential. (Differential operation will

be explained in the differential section of this article)

Rotational torque is delivered to the front wheels

through CV shafts. (CV shafts are commonly referred to

OPERATION OF THE FINAL DRIVEFINAL DRIVE FOR REAR WHEEL DRIVE

A RWD final drive sits in the rear of the vehicle, between the two rear

wheels. It is located inside a housing which may also enclose two axle

shafts. Rotational torque is transferred to the final drive through a drive shaft

that runs between the transmission and the final drive. The final drive gears

will consist of a pinion gear and a ring gear. The pinion gear receives the

rotational torque from the propeller shaft and uses it to rotate the ring gear.

The pinion gear is much smaller and has a much lower tooth count than the

large ring gear. This gives the driveline final drive ratio. The driveshaft

delivers rotational torque at a 90º angle to the direction that the wheels must

rotate. When installing or setting up a final drive, how the pinion gear

contacts the ring gear must be considered. Ideally the tooth contact should

happen in the exact center of the ring gears teeth, at moderate to full load.

(The gears push away from each other as load is applied.) Many final drives

are of a hypoid design, which means that the pinion gear sits below the

center line of the ring gear.

OPERATION OF THE FINAL DRIVE

FINAL DRIVE FOR REAR WHEEL DRIVE

Hypoid pinion gear teeth are curved which causes

a sliding action as the pinion gear drives the ring

gear. It also causes multiple pinion gear teeth to be

in contact with the ring gears teeth which makes

the connection stronger and quieter. The ring gear

drives the differential, which drives the axles or

axle shafts which are connected to the rear wheels.

(Differential operation will be explained in the

differential section of this article) Many final drives

house the axle shafts, others use CV shafts like a

FWD driveline. Since a RWD final drive is external

from the transmission, it requires its own oil for

lubrication.

TERMS

Hum means To make a low continuous

sound

Whine means Move with a whining sound or

Make a high-pitched, screeching noise.

Backlash means to moved back from an

impact. When the pinion move back from the

crown wheel or a gear move out of mesh.

Mesh means Contact by fitting together or

The act of interlocking or meshing.

Moderate means being within reasonable

or average limits; not excessive or

FINAL DRIVE ASSEMBLY