How to set up a 915 R&P?

[jfpound]

Greets All,
I'm rebuilding my 915 tranny. I'm a mechanical engineer and am not afraid of the details here but have found zero information of a good procedure for setting up the ring and pinion. I know what a good wear pattern looks like but I don' t want to do this by eye. Can anyone offer a good procedure for this or a source of the info? I have a Bently manual but it has nothing on R&P setup.

Thanks!!!

[Jim Sims]

factory shop manuals

[addictionMS]

use CRC brake squeal reducer or some other brightly colored thick substance to put on a few teeth on the pinion, put in the diff with ring gear, rotate, look at the wear patter, if it looks good your golden.

Make sure there is a tiny bit fo backlash, and your done

basically it is a trial and error, be sure to keep the preload on the diff bearings the same if you swap ouut the spacers, to get the endplay and backlash right

I am pretty sure Hayden will jump in and correct me if I missed something, he is always good at value add.

Jim

[addictionMS]

just finished swapping a 8:31 for a 7:31, so I am your man! maybe, I have a weekend on the trani and it all seems ok, next race weekend is the end of May, so if it survives that then i am your man

you will wnat to find a source for the spacers that go between the diff bearing and the diff, if you don't have a good selection, you will be wondering how to tell which one to buy, I managed to borrow a bunch, a couple of each, they start at 2mm and go upto about 3.6mm in .1 mm jumps.

until you have it appart you will not know what you need, and I was only able to get it right with trial and error,

Plus you will need a press, and some good two prong gear pullers.

plus do a search on the AutoX and Racing board, I posted a lot of questions and pictures over there on this project


Jim

[john walker's workshop]

generally speaking, you use all the shims that came with the donor R+P. (it should have come with them). the cases are pretty damn close to each other, so often, no shimming changes are required.

[wevoid]

I second Jim, Jim and John...

Firstly familiarize yourself with the set-up logic as explained in the factory manual. The information is on the gear pairs, you just have to understand what it means.

Secondly if you do need parts, then G50 and 996 parts (edit: diff carrier bearing shims) are also the same, so an enthusiastic parts re-seller shoud be able to help you get all the increments you need. Borrowing a kit of parts and replacing what you use is by far the easiest.

Thirdly, if you are doing a rebuild of the original CWP into it's original case, the only reason it would need set-up changes is massive wear or accident damage to the final drive housing, causing distortion - in which case a full set-up with the correct tools is the only real way to get it right.

Pinion shims are often damaged by the large roller bearing outer race spinning in the case. The edge of the bearing race scuffs and tears the pinion shims. Measure them (on the undamaged section) and replace them with the same total stack, if not the exact replacement parts.

Wear on the CWP can be corrected in two ways. Easiest for the home mechanic without the pinion depth tool, is to set pinion height same as it was (same shims) then adjust the differential carrier bearing shims to achieve the correct backlash.

As a general rule, backlash error (measured like the factory manual) is corrected with the same variation of shim size each end of the diff. e.g. backlach measures .26, requires .16 therefore .10 error, change diff shims by .10 - take .10 from case side bearing, add to cover side bearing.

Hope this helps.

Regards

Hayden

[addictionMS]

John,

I ran into the problem that the diff I was using was not the diff that came with the 7:31, and had a different setup. The early diffs have a thinner flange that the ring bolts to, and have that flange offset for the 7:31 set up. A diff of an 8:31 trani (later style) has a thicker flange, and an offset for the 8:31. So to put the 8:31 later style diff mated to the 7:31 pinion, you need to offset the diff in the case by about 2mm (give or take, I never actually measured it) so you do need a selection of shims.

Additionally I needed to space out the stub axle about 1mm so the flange for the CV cleared the seal in the case (pumkin side)

Also note the ring bolts for the later thicker flange diff are about 1/8 inch longer than the early thinner flange bolts.

Ji

m

[Tinker]

Jim,

Is that welding I see in that formerly open diff? Going for a locked rear end??? How does it behave?

Tinker

[addictionMS]

there is a report on the forst track weekend here

Jim

[jfpound]

Thanks for the help guys, you've made my life much easier! Happy racing Jim and best of luck!