Problems with pinion bearings

Question

Pinion Bearing Failures?

Answer

Porsche 968s have a transaxle gearbox, which means that the gearbox final drive and differential are all located under the boot between the rear wheels.
at the end of the gearbox output shaft is a pinion gear driving the crown wheel. This shaft has a big 'pinion' bearing on one end and a smaller one at the other end. A pre-load is applied by way of shims and a nut at the smaller end of the shaft.

If you have a pinion bearing problem it will be noticeable from about 35-40 mph when you will hear a whine. Test on a straight road with a smooth surface for minimum tyre noise. Close roof and windows, accelerate to 80-85 mph, lift off the accelerator, if you hear noise resembling a jet plane slowing down on a runway - you have a problem ! Alternatively you can secure the rear of the car on stands, run the car in top gear and listen to the noise from the gearbox. If you haven't got LSD you can stop one or the other wheels to eliminate possible wheel bearing and CV joint noise.
Cause: Too much pre-load on the pinion bearing at assembly. Getrag ( who made these transmissions for Porsche ) uses a computer controlled robot, which has not always been accurate.


Prevention: Check for leaks, correct oil level. It may be a good idea to change the oil at 20,000 miles or maybe even more often.

 
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