The document discusses the different types and operation of final drives used in front-wheel drive (FWD) and rear-wheel drive (RWD) vehicles. For FWD, the final drive pinion gear meshes directly with the ring gear which is connected to the differential. For RWD, the pinion gear receives torque from the driveshaft and uses it to rotate the larger ring gear, with many RWD designs using a hypoid gear setup where the pinion gear is below the ring gear. The ring gear then drives the differential and ultimately the rear wheels. Proper pinion gear positioning and engagement is important for both setups.

7. TYPESOF FINAL DRIVE
FINAL DRIVE USED
ON THE REAR
WHEEL DRIVE
FINAL DRIVE USED
ON THE FRONT
WHEEL DRIIVE

9. OPERATION OF THE FINAL DRIVE
FWD 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)

10. OPERATION OF THE FINAL DRIVE
FINALDRIVEFOR REARWHEEL 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.

11. OPERATION OF THE FINAL DRIVE
FINAL DRIVE FOR REARWHEEL 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

15. 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

16. FINAL DRIVE ASSEMBLY