Gears, need help!!!!

[Edgar Negron]

Thanks in adavance for any help. This is my problem, I had a shop install a set of FMS 3.73 gears, but the gears that were in my rear end were precision gears, which uses a different set up. This shop used the same shim that was in the pinion of the precision pinion gear for my FMS gears and they haul like a Wolf on heat, I took it back and the guy who put them on claims that he did everything right, so we argue for a while, and he won't fix them, well I din't pay him either. So can anybody tell me what is the shim size that comes in the 8.8 rear ends from the factory, when I check the one that is on now is .032" the pattern shows that the pinion is to close to the gears, at the hill of the gears. If I can get the right shim, I'll do it myself. Thanks.
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At this point, the only way to do it correctly is to actually measure the pinion depth. There is no 'factory' shim thickness; each rear is built up with the shim that it requires, it could be 0.005" or 0.032" or anything else for that matter. Now that you've used different gears from different manufacturers you'll need to actually measure the pinion depth and match it with the depth etched on the pinion. Pinion depth guages are pretty expensive ranging from $150 to well over $700. The kit I use is similar to the Zoom kit and runs more than $700 but its the best way to make sure the pinion depth is exactly what the manufacturer recommends. Keep in mind also that as you change your pinion depth, you're going to have to reshim the carrier to get the proper backlash and pattern.

The only way that you could take a shortcut is to remove the pinion bearing and hone it out with a brake cyliner hone so that it slips freely on-and-off the pinion. This will let you try several shims until you find the correct shim for the gearset. But its a long a tedious process since you have to install a shim, set the pionion up with proper preload (cut the locking threads off a pinion nut so that it goes on-and-off freely), then set up the carrier for proper pattern and backlash. The make the final assembly with a new pinion bearing. In the end though you'll probably still have a gearset that you're not happy with. That's why I always recommend finding a reputable shop to do the gear work. For a street driven car, its imperative that they're set up correctly or they'll always be problems. I think I'd look for another shop that can fix the problem.

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Jeff Chambers
T/S #3
11.611 Seconds/116.7 MPH
Chambers Racing Team

[jimberg]

Actually, the factory shim thickness is .030". But as Jeff said, it could vary. It's unlikely though since these rears are assembled on an assembly line. You can be pretty certain that those people aren't using pinion depth gauges and doing pattern checks. I recently did my gears and all the old shims were correct, but I was going from Ford gears to Ford gears. The left carrier shim is a standard size, too. .265" You will have to tweak that to get the back lash you want. You'll need a dial indicator.

To get the pinion depth you have to take the pinion head size and subract that from master housing dimension (4.415").

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351W 89 Mustang GT Convertible

When I worked at Dana during my college years, each and every rear on the assembly line was individually measured at assembly. Of course, they've got their own quick assembly tools to do so, but they were measured. The same was true of backlash, runout, and a final quick check of the pattern. We assembled alot of Ford rears at Dana, although none were the 8.8"; mostly truck rears for the Rangers and things like the Dana 44, 60, 70 and 70HD.


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Jeff Chambers
T/S #3
11.611 Seconds/116.7 MPH
Chambers Racing Team