Differential Assembly: Description and Operation
STANDARD REAR AXLEThe standard rear axle is a semi-floating hyphoid rear axle.
The rear axle housing carries the vehicle weight.
The rear axle is designed for use with the following components:
^ An open driveline
^ Coil springs
The rear axle has a hyphoid type differential ring gear.
The centerline of the differential drive pinion gear is located below the centerline of the hyphoid 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 wheels and tires. 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
The inner drive pinion gear bearing press fits onto the drive pinion gear.
^ The outer pinion gear bearing
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 recessed in the rear axle housing.
Tightening the drive pinion gear nut compresses a collapsible drive pinion gear spacer. The collapsible drive pinion gear spacer 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.
Placing selective drive pinion gear shims between the following components enables adjustment of the fore-and-aft position of the drive pinion gear:
^ The head of the drive pinion gear
^ The inner drive pinion gear bearing
Refer to Rear Axle With ABS and With Drum Brakes or Rear Axle With ABS and TCS
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 (1) between the following components:
^ The differential side bearings
^ The rear axle housing
Vary the shim thickness from side to side positions the differential case for proper differential ring gear-to-differential drive pinion gear backlash.
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
Refer to Rear Axle With ABS and With Drum Brakes or Rear Axle With ABS and TCS
The position of the above components permits them 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 the above components 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
Refer to Rear Axle With ABS Differential Assembly or Rear Axle With ABS and TCS: Differential Assembly
The above components 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 with the Antilock Brake System (ABS) have a rear wheel speed sensor reluctor wheel press fit to the differential case.
A wheel speed sensor is bolted to the top of the rear axle housing.
The sensor provides wheel speed information to the Electronic Brake Control Module (EBCM).
The rear wheel speed sensor reluctor wheels are an integral part of the rear axle shaft on vehicles that contain the following components:
^ The limited slip rear axle
^ The Antilock Brake System (ABS)
^ Traction control
The rear wheel speed sensor reluctor wheels are not separately serviceable.
The wheel speed sensor mounts to the rear brake caliper mounting plate.
Bolts attach the rear brake caliper mounting plate to the rear axle shaft.
The wheel speed sensor provides wheel speed information to the Electronic Brake Control Module (EBCM).
OPERATION
When the vehicle turns a corner, the differential allows the outer rear tire and wheel to turn faster than the inner tire and wheel.
The inner tire and wheel move more slowly than the outer tire and wheel. The inner tire and wheel 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 tire and wheel to move faster.
Limited slip rear axles have several definite operating characteristics. An understanding of these characteristics is necessary in order to aid diagnostics.
The energizing force comes from the thrust side of the gears. A free spinning tire and wheel may not have the level resistance to driving torque required to apply the clutch packs and the cones.
If the above condition occurs, applying the parking brake a few notches will provide enough resistance to energize the cones.
Energizing the cones is independent of acceleration. A very slow application of the throttle on starting is recommended to provide maximum traction by preventing break away of either rear tire and wheel.
All the rear axle components (except for the differential cases) from the following vehicles are interchangeable:
^ Vehicles with the limited slip rear axle
^ Vehicles with the standard rear axle
The slip rear axle differential case is similar in all respects to the standard differential case, with the addition of cone clutches splined to each side gear. The Auburn limited slip differential case is non-serviceable. The differential cases of the two vehicles are not interchangeable. The Auburn limited slip differential case must be replaced as a complete assembly. The following procedures are the same for both the Auburn limited slip differential case and the standard rear axle differential case:
^ Removal of the differential case
^ Replacement of the differential case
^ Service of the side bearings
^ Service of the ring gear
It is necessary to know the rear axle identification code (1) and the manufacturer's code (2) before adjusting or repairing the following components:
^ The repair axle shafts
^ The differential
The following information is stamped onto the forward side of the right axle tube or on a metal tag on the housing cover:
^ Rear axle ratio
^ Differential type
^ Manufacturer (2)
^ Build date (3)
RPO codes for the rear axle are also printed on the service parts identification label.
MAINTENANCE AND LUBRICATION
Drain and refill the lubricant on vehicles with limited slip differentials at the first 12 500 km (7,500 miles).
If the vehicle pulls a trailer, drain and refill the lubricant every 12 500 km (7,500 miles), with either type of differential.