Differential Assembly: Description and Operation
Rear Axle DescriptionStandard (Open) Rear Axle
The solid rear axle is a semi-floating hypoid rear axle, which is designed for use with the following components:
^ An open driveline (exposed propeller shaft)
^ Torque arm
^ Coil springs
^ One-piece or two-piece propeller shafts
The rear axle has a hypoid type differential ring gear. The centerline of the differential drive pinion gear is located below the centerline of the hypoid type differential ring gear. The rear axle housing encloses all of the components that are necessary for transmitting power from the propeller shaft to the rear wheel and tire assemblies. Bolts attach the rear axle housing cover to the back of the rear axle housing. The rear axle housing cover is removable in order to permit service of the differential case without removing the entire axle from the vehicle.
A universal joint connects the rear end of the propeller shaft to the drive pinion gear yoke. The drive pinion gear yoke has a splined end that fits over the drive pinion gear. The splined end of the drive pinion gear yoke also drives the pinion gear. Two preloaded tapered drive pinion gear bearings support the drive pinion gear in the rear axle housing. The races of the following components are press fit into the rear axle housing:
^ The inner drive pinion gear bearing press fits onto the drive pinion gear.
^ The outer drive pinion gear bearing combines a light press fit to a close sliding fit on the yoke end of the drive pinion gear.
The races of the inner drive pinion gear bearing and the outer pinion gear bearing press against shoulders which are recessed in the rear axle housing. Tightening the drive pinion gear nut compresses a collapsible drive pinion gear spacer. This bears against the following components:
^ The outer drive pinion gear bearing
^ A shoulder on the drive pinion gear
The drive pinion gear spacer performs the following actions:
^ Enables automatic bearing preload adjustment.
^ Maintains a preload on the inner drive pinion gear bearing.
^ Maintains a preload on the outer drive pinion gear bearing.
Enable the adjustment of the fore-and-aft position of the drive pinion gear by placing selective drive pinion gear shims between the following components:
^ The head of the drive pinion gear
^ The inner drive pinion gear bearing
The differential case is one piece. Two differential side bearings support the differential case in the rear axle housing. The differential side bearings are preloaded by the insertion of differential bearing shims between the following components:
^ The differential side bearings
^ The rear axle housing
Varying the shim thickness from side to side positions the differential case for proper backlash between the differential ring gear and the differential drive pinion gear.
Bolts attach the differential ring gear to the differential case. The following components have splined bores used for driving the axle shaft:
^ The left differential pinion gear
^ The right differential pinion gear
The position of these pinion gears permits the gears to turn in counterbored cavities of the differential case. The following components have smooth bores:
^ The upper differential pinion gear
^ The lower differential pinion gear
The differential pinion gear shaft holds these pinion gears in position. The differential pinion gear shaft mounts and locks in the differential case. All four of the gears mesh with each other. The following components turn freely on the pinion gear shaft:
^ The upper differential pinion gear
^ The lower differential pinion gear
These pinion gears act as idler gears when the rear wheels turn at different speeds. The following components back the differential pinion gears:
^ Differential pinion thrust washers
^ Differential side gear thrust washers
Vehicles that are equipped with the standard rear axle and the Antilock Brake System (ABS) only, have a single reluctor wheel mounted on the differential carrier behind the ring gear. A wheel speed sensor is bolted to the top of the rear axle housing opposite the reluctor wheel. This sensor provides wheel speed information to the Electronic Brake Control Module (EBCM).
Vehicles that are equipped with the limited slip rear axle, ABS, and Traction Control System (TCS) have rear wheel speed sensors mounted on the axle shafts just behind the axle flange. The axle mounted reluctor wheels are an integral part of the rear axle shaft and cannot be replaced separately.
Limited Slip Rear Axle
Limited slip rear axles have several definite operating characteristics. An understanding of these characteristics is necessary in order to aid diagnostics. The rear axle limited slip differential that is used is the Zexel Torsen (R) rear axle. The Zexel Torsen (R) axle utilizes parallel axis helical gearing to develop side gear separating force in an axial direction and planetary gear separating force in a radial direction.
A thrust block is used in the Zexel Torsen (R) differential for retention of the C-clip. The Zexel Worsens limited slip differential is non-serviceable.
The Zexel Torsen (R) limited slip differential case and the standard rear axle differential case are not interchangeable. The following procedures are the same for both the Zexel Torsen~ limited slip differential case and the standard differential case:
^ Removal of the differential
^ Replacement of the differential
^ Service of the side bearings
^ Service of the ring and pinion gear set
^ All backlash and tooth contact pattern procedures
Operation
When the vehicle turns a corner, the differential allows the outer rear tire and wheel assembly to turn faster than the inner tire and wheel assembly.
The inner tire and wheel assembly moves more slowly than the outer tire and wheel assembly. The inner tire and wheel assembly slows its (side) differential pinion gear. The side differential pinion gear is slowed because the axle shaft is splined to the side gear.
The differential pinion gears roll around the slowed (side) differential pinion gear. This action causes the other differential pinion gear and the tire and wheel assembly to move faster.
Rear Axle Identification
The following information is stamped onto the forward side of the right axle housing tube or on a metal tag on the housing cover:
^ The rear axle ratio
^ The differential type
^ The rear axle identification code (1)
^ The manufacturer's code (2)
^ The build date (3)
This information is necessary in order to repair or adjust the differential.
The RPO codes for the rear axle are also printed on the service parts identification label.