Drive Axles, Bearings and Joints: Description and Operation
Driveshafts
Purpose of the System
Drive on MINI is transmitted through the front steering wheels, consequently the design of these shafts is different to those on rear wheel drive vehicles, as a greater degree of articulation is required on the outer joints. Two different diameters of joints for inner and outer are used. The larger size is for the MINI COOPER S / Getrag 285 6 - Speed and the smaller for MINI COOPER with R65 or ECVT gearboxes.
Primary components of the Driveshaft System include:
- Driveshafts Left and Right Side
- Intermediate Shaft Right Side Only
- Support Bearing
- Outer Joints
- Inner Joints
- Front Hubs
System Components
The drive train for all three gearboxes consists of the same elements. A final drive, offset to the left of the center line of the vehicle by varying amounts. An intermediate shaft connects to the right hand side of the final drive with a support bearing at its outer end. The support bearing is fixed by a bracket and bolts to the engine block lower and ladder rail and incorporates the inner joint. This configuration in effect gives two drive shafts of equal length. The benefit of this is to reduce drive shaft derived torque steer that can be a problem on front wheel drive cars with un-equal length drive shafts.
Driveshaft Bar Shafts
The inner and outer joints are connected together by bar-shafts of solid construction but different lengths and diameters depending on the gearbox used. All outer joints have shields to protect the wheel speed sensors. ECVT and R65 have shields on the inner joints to protect the drive shaft seal. The MINI COOPER S has no need for a shield on the left hand inner joint due to the proximity of the inner joint to the differential housing.
Support Bearing
Outer Joints
To achieve greater articulation the outer joint has six ball bearings located in a cage running on convex grooves on the inner race and longitudinal elliptical grooves in the outer joint. The outer joint construction allows the joint to turn at the same speed as the shaft when in line and when the joint is turned through any position up to 45°. The name for this type of joint is "constant velocity". This design applies to the outer joints on all models.
Inner Joints
The inner joint is of the tripod type with spherical bearings to reduce sliding resistance. The joint has three bearings supported on needle roller bearings. This allows the shaft to slide horizontally inside the joint. The horizontal sliding movement will allow the overall length (differential to hub) of the shaft to increase or decrease as required with suspension travel.
A maximum drive angle of 25°. is possible with this type of joint but the working angle is normally less than 10°. This is why tripod plunge joints are normally positioned at the differential end of the drive shaft.
On the left hand inner joint, used with the R65 gearbox, the drive shaft it is retained in the differential by pressure from a spring located between the two halves of the inner joint.
On ECVT and Getrag the left hand drive shaft is located in the differential by a spring ring on the end of splines.
Front Hub
The front hub is a unitary construction with the wheel flange. The flange acts as the outer race of the outer bearing and is machined to take the outer race of the inner bearing. This hub bearing is of the ball type. The drive shaft is located onto the wheel bearings with multi-splines, and retained by a lock nut. The tightening of the nut provides the correct amount of pre-load on the wheel bearings.
Repair Information
Two different types of lubrication are used for the drive shaft joints. The outer joint uses a graphite-based grease and the inner joint uses high temperature melting point grease.
Drive shaft boots (inner and outer) are available to replace separately in the event of a split or damaged boot. The appropriate type of grease is supplied with the boot kit.
A BMW Special Tool will be available to aid the removal of the left hand drive shaft inner joint from the differential on the MINI COOPER with ECVT and the MINI COOPER S.
The tightening torque for the front hub / drive shaft retaining nut is:
- MINI Cooper = R65 (Manual) & ECVT (Automatic).
- MINI Cooper S = Getrag 285 6 - Speed.
Use only once.
Stake Nut Torque [M22 x 1.5] 182 Nm