C2-C3 axle end play

[Gary R.]

I was scanning through You tube and found this video on axle end play in a guys C3. Not sure if that person is here but this is a good example of a very common problem with 63-79 vette diff's, mostly from 73-79 but I have seen it in rebuilt diff's from just about any place. This guy is at a loss as to why he has excessive endplay in his diff. He has the posi out and apart, has the original axles and rebuilt axles and is still having issue.

The problem is with the posi setup, the clutch pack is loose, possibly from wear but most likely from setup. The axle faces he measures correctly and you can see the originals were close to .200" and the rebuilt one is .180-.185". Unless the posi is correctly setup, new axles are not going to help. In this case his originals are better then the rebuilt one but he doesn't know it. Any time I measure an original axle and it is close to .200" I reuse it, there is nothing wrong with it. The rebuilt ones are over the place, some under .180 and they will never setup correctly.

This can be fixed but not my using a 2nd snap-ring. Axle endplay comes from 3 areas in the diff.

1- Posi setup
2- axle face wear- soft faced from 73-79
3- enlongated posi case cross shaft hole. If not worn too badly the case can be machined and a larger diameter cross shaft and pinion spiders used. Those parts are going to be harder to find now though. The cross shaft should always be replaced during a rebuild as well.

Here it is if anyone wants to take a look.

https://www.youtube.com/watch?v=_Dh2zId7BbY

[Timothy B.]

Re: C2-C3 axle end play

Hi Gary,

So you are saying the posi set up needs to be tightened by a thicker shim behind the spider gears?

[Gary R.]

Re: C2-C3 axle end play

Hi Tim,
In a simple answer, yes. However, there is more to it then that. I never build a posi stock, with the springs and plates. To build it stock, each side gear is compressed and then the lash is measured between that side gear and pinion gear, then the opposite side gear is checked the same way. Shims are added until the lash is in the 001-008 range. Then you stuff in the springs and plates and that's it. This is ok and has been the way they were originally built and rebuilt. The problem is the spec range is too wide and there are several load ranges of springs that can be used. The steel clutches actually wear very little, I have measured them at 100k miles and have only found about 001-002" from the faces. The exception are the new fiber coated clutches, which rub off between your finger tips without much effort.

A tuned posi, correctly done, will eliminate the springs and plates and shim the lash/gears in several steps to get to a balanced, smooth rotation without and lash. In the case of the video I am confident it could have been tuned to the point of 005- 008" endplay in each axle. Interstingly I am now working on a 12 bolt conversion for a 72 vette and found the LH axle has 010" endplay with the tuned posi I built. I know the posi is correctly tuned and the posi is tuned to correct set up not to dial in axle endplay. In this case I kiss ground the face of the axle 003" before I sent it out for heat treating and cryo treatment. I suspect it might have been about 015" undersize to start with, which is uncommon, so the stock 12 bolt .150" c-clips are not thick enough. I usually grind them to size to setup 005-008 endplay. I have to get a 006" oversize c-clip to set it up.

Here is Tom tuning a vette 10 bolt posi with a 30 spline conversion. The one thing that is not covered is posi polishing which is just as important.

https://www.youtube.com/watch?v=CGq15JBBUQw