Pulled the diff out of my 69 to fix leaking front pinion, discovered broken clutch retainer and cracked posi. This was covered in a different thread. I have since found a new (used out of a 74) posi, new steel clutches tuned using Tom's method, new bearings/races installed. I'm trying to reuse my original gears since they were quiet when I pulled it. Before breaking the diff down I did check the backlash and patterned the gears however when I shim the case to get back to the same backlash as original (around 8 thousandths), my pattern looks weird to me. It seems like all of the information and patterns out on the Internet only show patterns for new gears and I'm having trouble diagnosing how to proceed.

This is all with the original pinion shim. That has not yet been changed.
Also, my original shims were even on both sides 0.240 thousandths. But in order to get the same backlash using this new posi I'm having to add more shims to the right side and take out from the left. Is this normal?

Here's what the gear patterning looked like when I first pulled the diff. Backlash was 8 thousandths. There was very little bearing preload, around 5 inch lbs:


Original drive side

Original Coast side

Now here is what I'm showing with the new posi, races, and bearings. Same 8 thousandths backlash and original pinion shim. Also preload is set to 15-16 inch lbs:

Drive side

Coast

Any advice on what my next adjustment should be? I played with tightening and loosening the backlash between 5 and 10 thousandths but that didn't seem to affect the pattern I am getting. I'm thinking maybe to try a smaller pinion shim?

 

Had time to do 1 more pattern tonight. I only changed the pinion shim. Went from the original 0.00323" to 0.00255". Pattern looks better to my untrained eye. The coast is still a little too close to the toe and the drive side looks maybe a touch too close to the heel? I think I'll try to get a shim combination just a little thicker.


Coast

Drive

 

Looks like you're heading the right direction.

 

If you did not have to replace the posi case then the original pinion shim would have worked. The lash I would set to 6-8. You go by the coast pattern with used gears and your last pattern looks like the original. The Drive is full but deep but that is wear. when you rotate the gears there should be a nice smooth mesh feel and sound.

When you tuned the posi did you get it where the cross shaft slides out freely in any position?