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.