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When using a donor cover plate for a shim tool, how does one know that the donor cover's bearing pockets have been machined to the same depth as the cover on the tranny being repaired?
Is it a matter of measuring both covers and making allowances for any differences?


Using a properly machined tranny shim plate of a known thickness, one has at least a known quantity to begin with.

I can see a few shims from Motobins in my future. As well as bearings, seals and gaskets. Yes, maybe two gaskets in case I stuff one up.
Hopefully I wont require any gears!

What about bushes etc that are in the tranny? Does one normally replace any of these as part of the job?

Compiling a mental picture for my upcoming tranny rebuild.......

I believe that the cover/shim plate serves as a reference based on the cover seam. The bearings protrude fron the plate by a meaured height, which is then used to shim the pockets of the real cover based on measured pocket depth from the seam (gasket surface.)

Hope I haven't mangled that thought beyond recognition.

Thanks Native, I understand the concept of measuring from the bearing to the bottom of the pocket in the donor cover, but I see a possibility of the two covers being slightly different in bearing pocket depth?
I haven't seen a donor cover yet to fully understand it.

The rear cover machined off is only to locate the shafts from moving side to side and hold the outer race from wobbling on the balls. How far it was originally machined matters none. Don't fret, just use it. You will see.

ME 109 wrote:Thanks Native, I understand the concept of measuring from the bearing to the bottom of the pocket in the donor cover, but I see a possibility of the two covers being slightly different in bearing pocket depth?
I haven't seen a donor cover yet to fully understand it.

The back of the "donor" cover is machined off to allow the height of the bearings races above the gasket seam to be measured. The bottom of the pockets of the donor cover are essentially gone, so there is no "depth" to the pocket. The bearing race height above the cover seam is the data you are looking for. When that height is inserted into the bearing pocket of the "for use in the real world" cover a certain amount of shims must be put into the pocket to meet the incoming bearing race with the specified clearance.

The world is truly a dangerous place when I am giving advice on rebuilding BMW trannys. So don't make me do it anymore.

Native /5 wrote:
The back of the "donor" cover is machined off to allow the height of the bearings races above the gasket seam to be measured. The bottom of the pockets of the donor cover are essentially gone, so there is no "depth" to the pocket. The bearing race height above the cover seam is the data you are looking for. When that height is inserted into the bearing pocket of the "for use in the real world" cover a certain amount of shims must be put into the pocket to meet the incoming bearing race with the specified clearance.

The world is truly a dangerous place when I am giving advice on rebuilding BMW trannys. So don't make me do it anymore.

Ah, a Reluctant Guru.
That explanation is so exquisitely clear, succinct and cogent that even I understood it. Thanks, Native.

Hey Jeff, wanna do a 'Bring-a-Box' tech session at mine this weekend? I'm keen to 'go in'.

The only other bush in the box is the first gear bronze bush which is no problem to replace.

There is a school of thought that says that you should replace all the circlips and spacers on the shafts, as they wear, and gear placement on the shafts can be critical, but I have no experience with this on a BMW box.
In any event they are in short supply right now, particularly the washer adjacent the first gear, number 16 on the parts fiche , which is currently unavailable - if anyone has the dimensions of a good new one I would appreciate it as the one on the box I am currently rebuilding is pretty beat up, and I would like to have one made.

Airbear wrote:

Native /5 wrote:
The back of the "donor" cover is machined off to allow the height of the bearings races above the gasket seam to be measured. The bottom of the pockets of the donor cover are essentially gone, so there is no "depth" to the pocket. The bearing race height above the cover seam is the data you are looking for. When that height is inserted into the bearing pocket of the "for use in the real world" cover a certain amount of shims must be put into the pocket to meet the incoming bearing race with the specified clearance.

The world is truly a dangerous place when I am giving advice on rebuilding BMW trannys. So don't make me do it anymore.

Ah, a Reluctant Guru.
That explanation is so exquisitely clear, succinct and cogent that even I understood it. Thanks, Native.

Hey Jeff, wanna do a 'Bring-a-Box' tech session at mine this weekend? I'm keen to 'go in'.

I feel thoroughly and exquisitely succed and cogged.

Major Softie wrote: I feel thoroughly and exquisitely succed and cogged.

Whatever gets you off, Major. We are an open minded lot around here.