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Eaton Posi rebuild

50K views 26 replies 14 participants last post by  big gear head 
#1 ·



This needs to be a sticky.

This is the guy that tought me how to build the Eaton Posi back in the '80s. This should be helpfull to many people.

This also works on the 8.5 Traction Lock, 9 inch, 8.8 and 7.5 Ford Trac Lock and sevral other differentials that use flat clutches. I go ahead and install the preload springs. Tom doesn't use preload springs. This is a choice that you will have to make on your own.
 
#3 ·
Thanks for this post, I thought this was a lot more difficult, Toms instruction takes away all the mystery. You said preload springs were a personal choice could you elaborate on the pro-cons? I'm having some issues with my unit and this exerscise is in the near future.:thumbsup:
 
#5 ·
The preload springs kind of help get the lock up started. As long as the clutches are tight then the springs are not needed much. Eaton has 200, 400 and 800 pound springs for different applictaions. The springs apply constant pressure on the clutches, so they will wear more when used on the street. If you do a lot of water burnouts then the 800 pound springs can help keep both wheels spinning while doing the burnout. I see a lot of cars with a posi, trac lock or other limited slip differentials that will start out spinning both wheels in the water and then one wheel will slow down and stop spinning. The heavier springs can help keep this from happening. If a car is used for drag racing then the clutches will need regular maintanance just like the valve springs, rod bearings and other parts.
 
#6 ·
Hi Freddie.
Do you think you can get another segment added showing how to do the springs? That would be GREAT.
 
#15 · (Edited)
I just posted links to Tom's tutorials on Aug 27th in my build thread because I happen to be rebuilding my posi carrier a few weeks ago.

There is more than one way to secure the axel. Having the axel in the vise vertically would not work without a customized axel so I laid the entire assembly out on my bench then locked the axel into my vise using the pipe vise on the lower part of the vise. This allowed me to adjust the preload by using different thickness shims then spinning the carrier to check for proper preload. I ended up using a .040" and .0425" thickness shims. Picture in the link following link.

I kept the ring gear attached for this part so I had more leverage to spin it as I had no ring gear wrench like Tom was using. You must remove the ring gear in order to install the spring pack. There is no room for the C-clamp otherwise.

http://www.chevelles.com/forums/showpost.php?p=6431074&postcount=45



I have a post showing how to install the spring pack into the carrier using a big C-clamp and some 1" wide steel bar stock. In my case I'm using stainless bar stock and a piece of hardwood to hold down the inside part of the spring pack while being compressed.

The little bolts you see in the picture are mandatory to hold the outside part of the compression plates together, it also keeps things from flying apart. I'm installing the yellow springs here but you can't see the yellow paint because it's only on one side of the springs.

First you tighten down the C-clamp about in the middle and put the small bolts into the outside holes of the spring plates. Once the bolts are in you need a couple pieces of 1/8" thick steel bar stock because you can't get a clamp far enough to the inside of the plate in order to make it fit into the carrier. The bar stock allows you to apply leverage to the inside part of the spring pack so that it can be inserted into the carrier. The picture is worth a thousand words.
http://www.chevelles.com/forums/showpost.php?p=6441506&postcount=46

In case anyone is interested. Tom is now working in the retail end of the business. I found this out by calling Tom's old listed phone number. A nice lady answered the phone but it's now a new business for selling differential parts. Very nice to deal with and overnight delivery in Cali. Use the link below for the new thegearshop business. This place actually sells single differential parts without having to purchase entire kits. They had one of Tom's hardened spider gear shafts which I purchased because mine was worn pretty badly, it's no wonder Tom has a hardened version.
http://www.thegearshop.net/store/cart.php

This is the best link I could find for setting pinion depth and backlash.
http://www.hotrod.com/techarticles/drivetrain/gm_12_bolt_differential_install_guide/
 
#8 ·
That would be great. Would you like a reminder ;-)
 
#11 ·
Thanks for this video, I just had an issue with a posi unit and this video answered my question!
 
#13 ·
If you want a really tight setup you can set the clutches at 0 as long as you use the GM differential lube. This is how I set mine up and the only clicking I get is when I back my car out of my garage (It's at a steep angle and I'm turning at the same time).
 
#18 ·
cool video,

Here is my deal, i had my posi unit rebuilt with 400# springs and during slow driving (parking lot maneuvering) the rear clunks real bad -- it sounds like a lockright unit but at the track i've done quite a few one leg burnouts. What gives?
 
#24 ·
Ok it's been rebuilt for a while now and for the most part it seems to be working.

But it still pops in reverse and on real light right hand curves. Pretty sure at the track last week it wasn't even fully engaging and letting one tire spin sometimes.

I've have 2 bottles of limited slip additive in it. Kinda figured it would have broken in by now.

Any ideas?
 
#25 ·
Sorry I'm late getting here. I hadn't noticed that you posted again. If this is a drag car then it's best not to use the additive in the oil. The additive makes the clutches slip easier, which is not what you want when drag racing. If it's being used for auto cross then the Eaton Posi is probably not the best differential to use. As for the popping, I don't know what's going on there. Did you use the GM additive?
 
#26 ·
I've been meaning to pull the cover and look for other issues like broken spider gear teeth or something.

I haven't been able to observe personally from outside the car but bystanders who noticed the popping when it was first built said it appear the axle was twisting then popping to unload like what happens with a car with a spool? It occurs in situations where the car is only slightly trying to turn, such as real wide curves on the highway.

The car is used for both and the original Eaton served me very well for nearly 10 years with no complaints. And yes, after a couple years I stopped using the additive in it.

I have 1 bottle of GM additive and I think the 2nd bottle was the Ford equivalent. Seems to work when the fluid is fresh and again got better when I very first added the 2nd bottle of additive.
 
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