General information
This Chapter is devoted to the description of the components used to transmit rotation from the gearbox to the drive wheels of the vehicle. These components include the propeller shaft, final drive assembly, and rear axle drive shafts.
Cardan shaft
Engine power is transmitted from the transmission to the rear axle by means of a two-section propeller shaft connected behind the so-called central bearing. «sliding clutch», splined sliding connection. The sliding clutch allows slight longitudinal movement of the cardan shaft. The front end of the propeller shaft is attached to the transmission flange with an elastic rubber coupling.
This clutch, sometimes called «Guibo», or «floppy disk», protects the cardan shaft and differential from jerks when the engine rotates. On some models, a vibration damper is installed between the transmission output flange and the flexible coupling. The middle of the driveshaft is supported by a central bearing mounted on a rubber cushion to dampen shaft vibration.
The bearing housing is bolted to the vehicle body. The front end of the cardan shaft is aligned with the transmission using a centering guide machined in the cardan shaft; the centering guide connects to the centering pin on the transmission flange. U-joints are located at the center bearing and at the rear end of the driveshaft to accommodate movement of the transmission and differential on their bearings, as well as any chassis deflection.
Differential/Final Drive Assembly
The differential assembly, located at the rear of the vehicle, includes the drive gear, ring gear (driven gear), differential and output flanges. The drive gear that turns the ring gear is sometimes also called the differential input shaft. It is connected to the cardan shaft by means of a flange. The differential is bolted to the driven gear and drives the rear wheels via a pair of output flanges attached to the drive shafts by constant velocity joints (SHRUS). The differential allows the wheels to spin at different speeds while cornering (the outer wheel must move slightly faster than the inner wheel due to the difference in turning radii). The differential assembly is bolted to the rear axle carrier and to the body with elastic rubber bushings.
Serious repair of differential assembly components (drive gear, ring gear and differential) requires a lot of special tools and fixtures, as well as considerable experience, and therefore it is best left to a BMW dealer or workshop.
Drive shafts and CV joints
Drive shafts transmit rotation from the output flanges of the differential to the rear wheels of the vehicle. Drive shafts are equipped at both ends with constant velocity joints (SHRUS).
The function of a CV joint is basically the same as that of a standard universal joint, but the CV joint can compensate for larger angles of deflection of the drive shafts than the universal joint. CV joints allow the driveshafts to drive the rear wheels, moving up and down with the rear suspension, even when the differential assembly, driveshafts, and wheels are out of balance.
Inner CV joints on all models are bolted to the differential flanges. The outer hinges are identical to the inner ones. Each hinge is packed with special grease and covered with a rubber protective cover. Regularly check the condition of the protective covers. Damage to the cover leads to contamination of the hinge.
The hinges on the vehicles described in this manual cannot be repaired, but they can be removed and cleaned during the replacement of protective covers. Both internal and external CV joints on all models must be replaced individually.