12 bolt rebuild

[ebaby35]

Just wondering if anyone has ever rebuilt their rear end. I have 12 bolt from a 73' or 74' which is currently a 6lug that I want to 5 lug and changed to posi and 3.73. I called a local shop and they said to clean paint bearings, posi,gears etc it would be around $1900. I'm not sure if that good or bad I know it takes time to do all this but is there anything I can do myself to bring down the price. can I do the whole thing myself?

[Firebirdjones]

I build a variety of them here for myself and others.

Sounds like you're asking for a positraction, gear, axles, etc.... In which case it sounds as though you basically are going to be starting with a bare 12 bolt housing and buying everything to go in it.

In that case you can quickly sink $1,000-$1,500 in just parts alone. Then you have to pay someone labor to set it up. Yeah it's not a cheap project to do it and do it right.

A good clutch style posi (what I prefer for street/strip) is about $450 for one with good parts inside of it.
A decent set of C-clip axles can set you back $300 or more.
I prefer US Gears, and a gear set is about $150-$200
A complete setup kit with all your bearings, shims, gaskets, crush sleeve, etc... is another $150-$200 depending on the brand you go with.

Set up can be labor intensive. I use a pinion depth gauge to set proper pinion depth. Some shops won't do this as it's more time consuming. Most will just look for a good gear pattern and call it done. I find I have to redo those types of rears because in most cases they whine. I'll use gear marking compound only after setting the pinion depth with a gauge, and proper backlash, just to see how the pattern looks. But a good set of gears are already lapped in according to the pinion depth and back lash settings that the gear comes with, so I prefer to follow those settings precisely. You'll be taking the pinion in and out several times to get it right, which means taking the pinion bearing on and off (I have a modified bearing that slips on without assistance of a press just for this purpose)
It's not something I'd recommend to a first timer all by yourself, but it's doable with the right tools and patients, maybe with a helper that knows the ins and outs..

[mattcrp1]

Hey Firebird, I think that is great advice. I have set up a ton of ford 8.8 diffs, and most are just overhauls from wear or abuse. The 12 bolts look a lot like the same set up i.e crush sleeve, pinion depth shim, and side shims.

In your experience have you found that the original pinion depth shim is close to what you measure with a pinion depth gauge? In the 8.8's I have done I have found the original pinion depth shim to be fairly close. Just curious.

Matt

[Firebirdjones]

Yeah the ford 8.8's are basically GM 12 bolts in a nut shell without going into detail.

You would be correct. When setting up a new gear set, to start off, I'll use the original pinion shim or shims to get me in the ball park. I find they are usually pretty darn close to what the aftermarket gear manufacture wants. Then tweak from there.