Differential Assembly: Description and Operation
GENERAL DESCRIPTIONThe rear axle assembly is of the semi-floating type in which the vehicle weight is carried on the axle housing. The center line of the pinion gear is below the center line of the ring gear (hypoid drive).
All parts necessary to transmit power from the propeller shaft to the rear wheels are enclosed in a Salisbury type axle housing (a carrier casting with tubes pressed and welded into the carrier). A removable aluminum cover at the rear of the axle housing permits rear axle service without removal of the entire assembly from the vehicle. The 8.9 inch ring gear rear axle uses a conventional ring and pinion gear set to transmit the driving force of the engine to the rear wheels. This gear set transfers this driving force at a 90 degree angle from the propeller shaft to the drive shafts.
The axle shafts are supported at the wheel end of the shaft by a roller bearing.
The pinion gear is supported by two tapered roller bearings. The pinion depth is set by a shim pack located between the gear end of the pinion and the roller bearing that is pressed onto the pinion. The pinion bearing preload is set by crushing a collapsible spacer between the bearings in the axle housing.
The ring gear is bolted onto the differential case with 10 bolts.
The differential case is supported in the axle housing by two tapered roller bearings. The differential and ring gear are located in relationship to the pinion by using selective shims and spacers between the bearing and the differential case. To move the ring gear, shims are deleted from one side and an equal amount are added to the other side. These shims are also used to preload the bearings which are pressed onto the differential case. Two bearing caps are used to hold the differential into the rear axle housing.
The differential is used to allow the wheels to turn at different rates of speed while the rear axle continues to transmit the driving force. This prevents tire scuffing when going around corners and prevents premature wear on internal axle parts.
The rear axle is sealed with a pinion seal, a seal at each axle shaft end, and by a liquid gasket between the rear cover and the axle housing.
LIMITED SLIP DIFFERENTIAL (LSD)
The axle assembly may be equipped with an limited slip differential (LSD). It is similar to the standard differential except that part of the torque from the ring gear is transmitted through clutch packs between the side gears and differential case.
The LSD construction permits differential action when required for turning corners and transmits equal torque to both wheels when driving straight ahead. However, when one wheel tries to spin due to a patch of ice, etc., the clutch packs automatically provide more torque to the wheel which is not trying to spin.
In diagnosing customer complaints, it is important to recognize two things:
1. If, both wheels slip, with unequal traction, the LSD has done all it can possibly do.
2. In extreme cases of differences in traction, the wheel with the least traction may spin after the LSD has transferred as much torque as possible to the non-slipping wheel.
Limited Slip Differentials impose additional requirements on lubricants, and require a special lubricant or lubricant additive. Use 80W90 GL-5 LSD lubricant.
REAR AXLE IDENTIFICATION
The rear axle identification number and build date must be known before attempting to adjust or repair the rear axle assembly. The Bill of Material and build date information (l) is stamped on the right axle tube on the rearward side.
The axle ratio is identified by a tag (3) which is secured by a cover bolt. If the axle has limited-slip differential, it also will be identified with a tag (2) secured by a cover bolt.