1972 differential carrier shims

[Billy O.]

I pulled my differential to inspect everything and noticed the right side carrier shims had were loose and had been chewed up on the inside diameter.

I've searched the archives and the internet and I see two styles of carrier caps; one style has a tab extending outward to presumably "capture" the carrier shims and the other style (as mine is) without the tabs. It looks like my differential is not original (looks like it is from a '68 or '69) Surely GM didn't intend for the preload of the carrier bearings to be the sole means of preventing the shims from backing out did they? Is there supposed to be something in/about the cover that is supposed to retain the shims?

Any help is greatly appreciated.

Billy

[Edward J.]

Re: 1972 differential carrier shims

Billy. I just finshed my 72 rear diff. sound to me like theres not enough shim, the should be some resistance when install ing those shims to pre-load the side bearings. there should be one thick spacer and maybe one added shim the make the pre-load on the side brg. and you must have alittle back lash when finished abour 4to5 thousandths. all the shims and thick spacers are still av. at you local gm dealer. one other note the thick shim goes outboard and smaller shim inboard (closest to the bearings)this should the caps to hold the shims in place with the caps bolted and torqued.

[Billy O.]

Re: 1972 differential carrier shims

Ed,

Thanks for your reply. Did your caps have the tab extending outward?

The problem with my setup (and I understand what you mean about the thinner shims being behind the thick shim under tha cap) is that my caps, without the tabs, leave a wider gap between the outboard side of the cap and the inside of the housing. I think the thick shim is around .235"-.240" and it easily passes through the gap between the cap and the housing.

I'll make a couple of photos and post which may reveal something I'm missing although I'm starting to worry I have a "mixed matched" set of caps/housing/shims.

Billy

[Gary R.]

Re: 1972 differential carrier shims

posi case shims should be tight fit to preload and maintain backlash,yours are too loose. The factory shim was a cast iron one piece shim ground to size. These are usually not reused in rebuilding unless they are still the correct size( not usually) and a case spreader is used.
If you find steel stackable shims they are aftermarket and someone has been in there before.
The bearing caps are bored to size and are specific to each side. If someone was in there (and knew what they were doing) there will be witness marks of some sort on the caps. The cast in tabs came out around 71 I believe. Doesn't matter thousands have been built with the caps like you have. The 63-64 caps are wider and rougher looking.
If you are unsure which side is correct you can check the "rock" with a bearing race to see what the gap is between the pad and cap. Should be about 001 +/- 0005". Too big a gap will clamp on the race and burn them up, too loose with let the race spin in the bore.

Here is a 65-68 diff with the early eaton posi(prone to crack) and the caps like you have.


Here is a C3 diff I built with a steel cap fit on the LH and the tabbed cap on the RH.



checking the rock- this should be done with every rebuild, and corrected if need be.

[Billy O.]

Re: 1972 differential carrier shims

Hi Gary,

Thanks for your reply and help. I can't quite see from your photos if the same gap exists between the outboard face of the bearing caps and the housing as in my differential. The gap I have is a little over .250". My left side shim is less than .250" thick (so it is not "captured" under the cap) and it is cast iron. At least one of the two on the right side which were chewed up from the axels looked to be cast as well. There was absolutely no interference fit when I pulled the carrier out.

So......I guess what I'm trying to determine is with the non-tabbed bearing caps as I have, are the shims supposed to be captured under the caps or was the original design intention that the preload (appx. .010") supposed to keep the shims from backing out?

Billy

[Gary R.]

Re: 1972 differential carrier shims

Billy
Those are the factory iron shims,ground to size to produce the correct backlash and preload. It is not uncommon to find loose ones as these were slapped together at times like any production assembly. You need to check the lash and gear pattern, loose those shims and use steel shims to set up. Once properly setup they will not slip out without effort.
If you find you can't get a good pattern or the pattern ends up off the heal you need new gears.