Need some help setting up my 12 bolt

[NovaPwr]

Hey guys, I need to get the shim right on the pinion. Read every thread over the weekend I could find on this subject. The gears were the original GM's. New ones are US Gear. Can I get the shim size I need by looking at the end of these two pinions? The one is original GM. ( I will know the factory shim size as soon as I get the bearing pressed off)

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I am going to go get the bearings removed right now. If there is no way to determine a shim thickness this way would honing out the old pinion bearing, so it slips on easily, then running up the bearing preload without the crush sleeve, be the best route to go here?

Also, the yoke was hard to get off, I used a brass hammer and hit the old pinion end to drive it out but would not want to hit the new pinion like that. Should the yoke fit that tight? Is there a puller for that? You do need to install it to run up that preload don't you?

I mic'd the two carrier shims, more like big washers. I read you should add .003 for bearing settling? I noticed the carrier rolled out by hand and I did not have to pry it out. It was snug but by no means required a pry bar to come out. I know there are some good rear end guys on here so I really value the advice.

Lastly, I could not find a link on rebuilding the eaton posi. I have a new factory style clutch pack and want to install it while this is apart. I have a service manual for 1972 and it shows them doing an Eaton from a 10 bolt using the 1/4 " bolts and c clamps while driving the cage out....is this the same as the 12 bolt? Do you need any special tools to do this job?

Sorry for so many questions, just want to get this thing in right the first time around. This is new territory for me. Thanks guys.

Dave

[GeoffP]

I can't offer any help other than to say I'm also interested in hearing how this turns out. I plan to put gears in the 12 bolt in my Camaro soon (and want to do it myself).

[chicane67]

1. What ratio are you installing ?? It doesnt matter what's coming out as you will most likely not use that depth setting anyway.

2. I would recommend that you do the honing of the inner bearing idea... especially if this is your first differential.

3. Yes, the yoke should be that tight. Use an aluminum drift (I use a 1" square piece of scrap about 12" long) and then just take a couple of good swings. But make sure you dont hit it out the back of the housing.

4. You realy need "Super shims" for the carrier bearings... unless you have box of factory one piece shims laying around.

5. The only real tricky thing to the re-building of the Eaton... is the spring preload pack... and rolling in the spider gear thrust washers.


...If you get into a pinch... PM me your phone number. I will be available today... but not the rest of the week.

[NovaPwr]

1. What ratio are you installing ?? It doesnt matter what's coming out as you will most likely not use that depth setting anyway.

A set of US Gears 3:73's. The carrier had a set of 3:08 's in there.

2. I would recommend that you do the honing of the inner bearing idea... especially if this is your first differential.

Well, I just finished that up, used an 1 1/8 socket wrapped with some 80 grit from the cabinet shop. Worked out really well.

3. Yes, the yoke should be that tight. Use an aluminum drift (I use a 1" square piece of scrap about 12" long) and then just take a couple of good swings. But make sure you dont hit it out the back of the housing.

OK, I will find a pc. and put something soft back there.

4. You realy need "Super shims" for the carrier bearings... unless you have box of factory one piece shims laying around.

This Yukon kit has a pretty good assortment of them in it. Hopefully they will work.

5. The only real tricky thing to the re-building of the Eaton... is the spring preload pack... and rolling in the spider gear thrust washers.

OK, sounds like the instructions I have on doing a 10 bolt. I assumed they might work the same but you know what they say about assuming things : )


...If you get into a pinch... PM me your phone number. I will be available today... but not the rest of the week.

Thanks a bunch! I will do that.

Dave

[chicane67]

What you are showing there is a set of USGear 3.73's...

I'll bet that your final depth will be 0.036 or 0.037" depending on what you put into it for lash.



I would drop a 0.036" depth shim onto it and shoot for 0.009 to 0.010" to start with.

[big gear head]

The Eaton posi is not a problem. Did you new clutches come with shims? You need to shim it so that the clutches have the correct preload. The springs and plates go in easy if you use smoe channel locks to compress the pack and puth it in.

You can't use the original differential shims. You need a shim set so that you can adjust the backlash and bearing preload.

[NovaPwr]

[quote=big gear head;502196]The Eaton posi is not a problem. Did you new clutches come with shims? You need to shim it so that the clutches have the correct preload. The springs and plates go in easy if you use smoe channel locks to compress the pack and puth it in.

I had to take out one of the original shims on each side to get that clearance they showed in the book. Boy those two side gears were a royal pain to get in there! Hopefully it will work well. Specs said .001 -.006. One side ended up almost at about .005 and the other was about a .002 Hopefully they don't have to be exactly the same....? Thanks for the info.