12 Bolt Rear specs...

[chevjayfsd]

We are going to be rebuilding the 72's rearend, and just need to know what it is... It's a 12 bolt with 3.08's... We are going to do a posi 3.73 setup, what all do we need, like what carrier, how many splines does my 12 bolt have? etc. etc.

Jason

[EFI70Blazer]

You will need a 4 series truck carrier for 3.73 gears. Axle's are 30 spline, so your carrier will need to match that. Other things you will need are an install kit. This kit comes with shims, bearings, chrush sleeve, bolts, pinion nut, gear marking compound and everthing else you should need to set one up other than tools. Getting the bearings on and off without damaging them requires special tools, like a bearing seperator and a press. If you are just going to cut the old ones off and put on the new ones, you might want to have the inner pinion bearing pressed off. By saving this one you can take a die grinder and hog out the inner part so that it slips on and off the pinion gear easily. This way when you are setting up your gear mesh you can easily change shims without having to use a press and bearing seperator. If you need help setting everthing up, just PM me and i will try to explain. Here is another thread that i explained things a little more.


http://67-72chevytrucks.com/vboard/s...aton+posi+3.73

[whatnow123]

Wow.. do you need to do all that if you are just changing to a posi carrier?

[EFI70Blazer]

Originally Posted by whatnow123

Wow.. do you need to do all that if you are just changing to a posi carrier?

For the most part yes. In rare cases you might get lucky without having to set up the gears again, but most of the time you do.

[2500HD]

I just finished doing this (373 and eaton Posi). I have never done one before and I am no expert but here are some issues I encountered:
1. We started with .035 shims on the pinion as recommended in the instructions. This was to much and ended up with .030 and would have been better with .025.
2. Without a bearing press plate, the pinion bearing would have been next to impossible to remove without damage.
3. Pinion bearing races were difficult to remove. The new ones went in OK but they are countersunk you will need a plan to seat them properly.
4. The crush sleeve is actually called a spacer in the instructions and there is no mention of the force it takes to crush it. My impact did not even come close to crushing it. We finally got it crushed with a 3/4 in drive socket holding on to the trailing arm and pushing with my legs. Dont crush to far.
5. If you are doing this with the rear end still in the truck, make sure to have you jackstands high enough so you can sit up under the truck. There is a lot of in and out and would be difficult laying on your back.

It is all back together, broke in without noise. The install kit does not come with axle bearings and seals and you may as well do them at the same time.

[Psycho71]

While I haven't done the posi carrier, I have rebuilt my whole rear end. The above advise is dead on. I suggest taking it out of the truck, making everything readily accesible. But other than that, I'd agree that you should go ahead and replace the outer axle bearings while you've got her torn apart.

Jay