Ford Mustang Forum banner

8.8 Posi rebuild/gear swap, no pinion shim!

6K views 15 replies 4 participants last post by  NotTheStig 
#1 ·
Hi there,

So I'm rebuilding my 8.8 rear end, doing a 3.73 Ford ring and pinion swap with all new bearings.

I pulled the bearing off my old pinion gear (destroying it in the process) to retrieve the shim to put on my new one, only to find there was no shim!

It's my understanding these should ALWAYS have a ~0.030 shim, and you need that to set your gear mesh and backlash baseline on the new gears. Is it possible someone did an improper rebuild in the past and lost the shim? or has anyone heard of one of these coming without a shim at all? What should I do with the new pinion gear, should I try and assemble it without the shim? After the difficulty removing the old bearing from the original pinion gear, I don't have high confidence I can remove and reinstall it again if it turns out I need to add a shim.
 
#4 ·
I called around before starting this and couldn't find any shops that did this kind of work locally, which is why I started this project myself... I'll look around again and see what I can find.

Sometimes, depending on the gear, they dont require a shim. What you are going to want to do is buy a new pinion bearing and race and then buy another of the SAME exact bearing. There are two different bearing/race combos and they do not mix well. Take your second bearing and hit the inside with a die grinder or dremel just enough so that it slides on to the pinion with little resistance. When you do this, you can set the gears up and run a contact pattern before pressing the bearing on. Once you find the correct shim and your contact pattern and backlash are good then pull it apart and press the new bearing on with the correct shim.
So I bought a USA Standard Gear 8.8 master overhaul kit, and after reading your advice and spending a whole lot of time and effort* researching, I tracked down the manufacturer, who sold the bearing only as part of the $90 kit, and I got a part number from them. It's a Japanese Koyo M802048 tapered roller bearing. I've looked all over and can't find any way to order this bearing and have it be here by this weekend, when I need to start putting the diff back together.

When I talked to the rep, he insisted that any M802048 bearing would be the exact same part from the same manufacturer, but further research has revealed this is not the case. I can find a Timken M802048 bearing and have it here by Friday for $13. Timken is allegedly American made, but the part origin is China....

So my question is, if I buy a Timken bearing to grind out and make a template, can I then press on the Koyo once I've selected the right shims? or should I perhaps just buy two Timken bearings and throw out the Koyo I have? or is there perhaps a better way of going about doing this I haven't thought of?

EDIT: The Timken bearing comes without a race. Can I use it with the Koyo bearing race?
 
#3 ·
Sometimes, depending on the gear, they dont require a shim. What you are going to want to do is buy a new pinion bearing and race and then buy another of the SAME exact bearing. There are two different bearing/race combos and they do not mix well. Take your second bearing and hit the inside with a die grinder or dremel just enough so that it slides on to the pinion with little resistance. When you do this, you can set the gears up and run a contact pattern before pressing the bearing on. Once you find the correct shim and your contact pattern and backlash are good then pull it apart and press the new bearing on with the correct shim.
 
#8 ·
Go to the parts house and get what they have, most of the time its timken. Get 2 of those and one matched race. Use one for setup and the other for final assembly. I wouldnt just throw it together the way it was before because of gear manufacturing differences and the other guy may have set it up wrong.
 
#13 ·
update

sourced the bearings, races, did as suggested and created a template bearing for testing. It's been in and out several times now. First i tried without the shim and it was WAY off. Then I added shims and got a lot closer. Been fine tuning adjustment since, but I kinda seem to have hit a dead end in progress and I don't know where I'm at. See below linked pictures.

Coast side (bottom paint) http://i.imgur.com/327rmiY.jpg
Drive side http://i.imgur.com/axQbnbm.jpg

Do you think this is close enough? the drive side is neither near the root nor top, but is definitely near the toe (top toe is thicker pinion and root toe is thinner pinion) Coast side is much closer to the center, probably as good as it is going to get, really, although the pattern isn't even. These are used gears so I've heard the coast side is more important? I don't know, should I try going thinner pinion some more to see if the drive side moves centerward, or should I just leave it and move on to final assembly? I really want to just be done with it at this point.
 
#16 ·
Soooo.... while everything looked good with the test bearing, I decided to do a final assembly with the new crush sleeve, nut, and new bearing... after getting it all together again, the gear pattern was WAY off again! I didn't change anything, used the same shims that came out perfect in testing, same exact model bearing and everything. Now I'm stuck starting over from square one, tearing it all apart again and ordering new crush sleeve, nut, and bearings. UGH! This is so infuriating!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top