Need help putting together my 12 bolt

[malc]

I have a 12 bolt differential with a 2.56 peg leg originally out of my Caprice. I have an GM Posi and 3.73 gears. I want to put it together, but never done this before. I know I need a bearing, shim, etc kit. Local shop wants $400 labor to do it. For that much, I would rather learn to do it myself, even if it I need to buy a $100 specialty tool. I have the factory overhaul and service manuals, but looking for input from people who have done it.

Greatly appreciated.

Are they used gears ?
If they are and you didŽnt do a gear pattern check before they were removed youŽll have trouble setting them up.
ItŽs a good idea to do the check and take pics then youŽll know what youŽre shooting for on the final assembly.

[TheSilverBuick]

I wish I knew about that bolt a bar to the yoke trick!! I'll use it next time for sure! The part I've always hated most was that damn pinion nut.

Get the real grease, ended up finding it at jegs, and then make sure it all comes off before final so you dont foam your fluid.

Hmm, the little bit of grease foams the fluid? I honestly don't know but have not heard of that and can't quite understand how? I bought a tube of the gear pattern grease at a tractor (Catapillar) store.

[malc]

Get the real grease, ended up finding it at jegs, and then make sure it all comes off before final so you donŽt foam your fluid.

Like this......

[anotheridiot]

I'd be curious to see how many of you re-use the crush sleeve. I know I've done it a couple times and never had a problem.

I reused one I was setting up with, didnt get that pic from Malc about his fixture he maid, plus I was building it on a set of 3 foot tall jackstands I welded together to support the camaro under the rotiseree. I actually ended up sanding mine down and deburring it to get the preload right. At least all the slop I started with is gone, it moves smooth forward, a little clunk in reverse. Its how we learn I guess.

[kyhunter89]

i've done three or four now, never had to change the bearings, I agree with squirrel. Never had a bearing failure, I've also also reused the crush sleeve from the new(used) gears i'm putting in. Even when swapping to the tru-trac everything was on the money reusing all the old stuff. Never had any make noise either. I'll account it all to luck.

[squirrel]

you're not supposed to use a whole tube of marking grease on one rearend! just a dab'll do ya'

[malc]

Depends on how worn it is. The old crap I usually work on is worn out, you can't get any torque on the pinion nut without having too much preload. The redneck way to fix it is to shim the crush sleeve, but that won't last long, and as the shim gets eaten up it puts metal in the bearings.

The crush sleeve doesŽnt wear.
ItŽs there to hold the bearings at the right preload and is used on the axle assembly line for speed.
You could use a solid spacer with shims but that is more difficult to set up.
If you had a used crush sleeve crushed to 15inlbs you could probably get a little more out of it,
like they suggest you do when changing the front seal.
IŽm using this type of crush sleeve from Ratech. http://www.summitracing.com/int/part...1003/overview/ FOUR so far...

[squirrel]

I know the crush sleeve isn't supposed to wear, but in real life when they get a lot of miles on them, they do wear and get shorter. The pinion bearings do spin on the pinion. This is on old stuff that's worn out, which is what I'm always working on.

Common on the 55-64 chevy rearends is that the pinion yoke gets worn so much were it contacts the pinion bearing, that it becomes too short, and the nut bottoms out on the pinion, instead of clamping the yoke like it should.

[Casper]

Yea I need to be ordering a posi unit for my Formula pretty soon, for now the gears that are in there will do.

[malc]

Get yourself one of these, Differential, Lock-Right, Locker IŽve had one since 1995, no maintenance.

[Scott Liggett]

I have one on my Caprice's 12 bolt. Works Ok. Has had some issues.

[Loren]

Scott, the first time I ever tried to do a rr diff, it was a mess...I just stood there looking at it all, thinking w.t.h... I was just switching to a posi I pulled out of Pick-Your-Part, back when you could drop in there and count on finding at least one, so all I had to worry about was the side-to-side which you set by measuring lash w/ a dial indicator so it wasn't too bad. So, the first thing I needed was patience, which after all everyone should have or learn to, and the second thing was a dial indicator w/ a magnetic base which any serious car guy should also have (you can use it for engine building, cam checking etc.). That's all the rr end work I did for a long time, but then eventually it was time to do a whole gear set.

Approaching things kinda in the reverse of normal, it was time to face the deal with the pinion which miffed me even more. Obviously you have to start with the pinion. There is a bearing at the back and one at the front which are a lot like the deal with front wheel bearings (it helps if you think of it that way), then pre-load between the two is critical (as in wheel bearings only more so), you measure that by turning things using the inch-pound wrench to measure turning force when you think you're close. What's different than wheel bearings is that there needs to be something solid (more-or-less) between the bearings which in the case of the twelve-bolt is the crush sleeve that gets squished in there and stays to take up the space, and that the final depth of the gear in the case (relative to the carrier bearing bores) is important and has to be set to a spec. So thirdly you need a pinion depth measuring setup, which is the most special tool here that won't get used for anything else. BTW that crush sleeve (which if you crush too much is trash) is not used in all rear end types, some use a more solid deal with shims).

Adjusting that depth means installing the bearing race onto the pinion shaft using a pipe or sleeve of some appropriate size (fourth thing, just McGyver it) assembling to the right turning torque then measuring where it comes out the first time (again, relative to the carrier bearing bores by using the depth tool), then getting a shim combination to correct whatever you got and pulling the bearing off again and sticking them in there. So the fifth thing you need is one of those H-frame presses from Harbor Freight. That will take up room in your shop and be a hassle to move for the rest of your life, but when you need one you need it. You may have to slip bearings on and off again a number of times to get it right so it needs to be made easy, so you also need (sixth) one of those clamp setups that grips into the tiny bit of the backside of the bearing you can get a bite on, to pull it off.

After you've taken three frustrating nights out of your week to do what a pro would do in minutes smoking a cigarette, it's time to stick that heavy carrier in there with whatever bearings you're using (old, or new ones pressed on with your press). It should drop in to the right enough so that there is some looseness between the gears at first, then you add shims under the pressed-on inner bearing race so that, side-to-side, until it's tight the right amount (it will take a little force to get it in and always make sure you're left with some looseness between the gears so that one jamming against the other is not skewing up your pre-load figuring). You will squash a finger at least once doing this and be going through paper towells and keeping things clean with compressed air. With that in order you can position your dial indicator against one of the ring gear teeth in line with it's motion as much as possible and measure "lash" which on a used set should be more than what the "new gear" spec would be (like, .012-.015"). Since you can't directly translate your measurement to a shim thickness adjustment as with the pinion, you have to kinda guess but since you had your bearing preload dealt with, whatever shim comes off one side under the bearing goes onto the other. Again, pulling bearing inner races on and off, on and off, and making sure they're on all the way when you do so.

When it seems like you've finally got that in order (you've got a week's worth of evenings plus a Sunday into it now) go ahead and try some marking compound but do this with used gears: With some heavy magnification do your best to figure out what the wear pattern (like, as with a "witness" mark) was before in their prior running and consider that along with what the ideal pattern should be (which will obviously be a long oval area in the middle of the tooth area - the gears are ground to support that). Hand-load the gears against one another when running the marking compound and know that there will be some flex, even in those heavy machined parts as they run under torque so what you see is not completely totally what you'll be getting in use but there's not much you can do about that.

Did I mention, by Gosh try to be able to do all this with the diff out of the car supported at working height so you can do this sitting in a chair. It could be sitting on a stack of tires, whatever.

When you're all done you've bought a couple hundred bucks worth of tools and possibly invented two new swear words but you did it yourself and were not hostage to some guy in town who'd like your $400 but is gonna bitch about setting up used gears and not guarantee them because of that. That's the part I like, and why I will never have gears set up for me again.

Don't throw those 2.54's out, I'll buy them from you.

[squirrel]

I'm glad I started messing with this stuff in high school....

[Loren]

It helps, grasping concepts when you're younger. Otherwise you may be spending half your energy just fighting your own head, on your way to getting the result you know is needed.

By the way I should mention, the above is just my own take, meant to go along with all other info here as well as (of course) the official stuff.

[Scott Liggett]

Thanks for info, Loren. A buddy a work volunteered to do it for a case of beer. I will have to wait, though. He is busy planting his fields right now. Then I will have to plead for time while he gets his pulling truck ready for the season.