harrisonrick

can you change these after taking CV axles off WITHOUT dropping the transaxle?

Oddjob

No.

You need to pull the differential out of the case, which requires dropping the trans, and disassembling the gear carrier assembly from the main casing. Bearings are on the ends of the diff, the bearing races are pressed into the trans case housing on one side and on the diff cover plate on the other side.

After replacing, you need to check and possibly reshim the R/P backlash.

Van

Or you'll be going back in their shortly after -- ask how I know...

Mike C.

Ditto. Unfortunately, changing these does entail all of the work required to re-shim the R&P for proper gear mesh. Removing the transaxle from the car is the EASY part....

harrisonrick

I thought you'd only need to reshim the ring and pinion if you replace it with an LSD or do other work to it?

I know the bearings have shims that can be replaced if necessary.

Damn it all to hell.

Van

The diff, whichever diff you have, holds the ring gear. The pinion gear's location is fixed in the case, but the whole diff assembly is supported by those bearings. If the new bearings differ in the slightest due to manufacturing tolerances, then that whole diff assembly could shift to the left or the right, or be too wide or too narrow -- causing an improper mesh with the pinion gear and perhaps accelerated bearing wear.

If you reuse the same diff and ring gear, you can probably get away without worrying about shimming the pinion shaft...

Mike C.

Maybe but you will need to come up with some way to measure the backlash of R&P and unless you want to risk ruining the them. My understanding is that if the R&P don't mesh properly you will hear some howling and/or growling and accelerated wear of R&P. I would also check the R&P mesh pattern one you have the backlash dialed in.

Oddjob

Yes, if improperly set, it can make noise and if the mesh is bad enough, it can cause premature/irregular wear on the R/P teeth. Improper preload on the pinion will also cause pinion bearing wear problems.

There is certainly a possibility that R/P failures on 944 n/a's are in part due to a poor R/P engagement pattern (either from a poor rebuild or from slop due to high mileage/worn bearings). Obviously, the main problem with the n/a failures is that the R/Ps are not excessively oversized for the power/torque application (unlike Turbo and S2 R/Ps which are very strong).

I have heard the "rumor" that if you replace the original factory installed bearings, with OE Porsche bearings, during a trans rebuild - the factory bearings have a tight enough tolerance spec that the odds are pretty good (maybe 3 out of 4) the original shims will keep the backlash within spec. But real p-car shops will always check to confirm/verify. And I have not confirmed this myself, so I cant recommend taking this risk.

If you are swapping differentials, or use generic/aftermarket bearings, all bets are off and the backlash will need to be reset (for a diff and diff bearing change) and the pinion depth and preload (if changing the pinion bearings).

By the way, why do you want to change the diff bearings? Pinion bearings take the majority of the load in the trans, and usually wear out first. They are the bearings that you can hear whinning and rattling on worn transmissions.

harrisonrick

Jim...pm sent. Thanks!

I was hoping the noise I'm hearing was the diff bearings, but by the sounds of things the r & p bearings are the cause.

Well, ****.