A friend of mine rebuilt my ford 9" rear with Richmond 411's, Richmond bearing and shim set and a US posi (I don't remember the brand) I put in last year.
The posi unit has less than 1K miles on it, so I didn't replace it.
He brought it back Friday and showed me the problem he is having with it - when you put a dial indicator on the side of the ring gear and check the runout, there is 0.007 difference 180 degrees apart on the ring. That makes the backlash impossible to adjust. It looks like the posi was machined
with that .007 difference on it, because it doesn't matter if you put the dial indicator on the posi or the ring gear - the runout is still the same.

Has anybody ever, or do you know if you can shim between the posi and the ring? I don't know if I would like to do the because there is a lot of torque on that gear...

 

No you can't.

But, you might try turning the ring 180° on the carrier, and see if that helps. Before you do that, mark the high spot on the gear and see if it's still the high spot after you turn it. If the high spot stays in the same place on the gear, then the gear is fornicated; if the high spot is now 180° away from where it used to be on the gear, then the carrier is the problem. If the problem disappears, then it was an assembly problem, or the carrier and the gear are each about .0035" out of whack. In that case, assembly problems are more likely I would say.

 

Is it possible to do this without taking the whole thing apart again? Can I maybe pull the bolts holding the ring to the carrier with everything still assembled?

 

Be careful when measuring backlash that you aren't clunking the gears. If you do, the pinion yoke might walk a little and provide poor results. It might even seem repeatable. I made this mistake and was measuring about .004+" variation before I realized what I was doing. Afterwards I measured less than .001" variation.

When measuring the runout, try to turn the ring gear VERY slowly so that you can watch as it passes through each .001 on the dial indicator. When it stops your there.

If your positive you aren't walking the pinion, then the other advice applies.

BTW: Has anyone else ever done what I did when measuring their backlash? I finally realized that if I kept banging one side that I could slowly walk around my dial indicator scale showing me that I was definitely moving the yoke even though it was not noticeable otherwise.