Advise needed on broken posi


Veteran Member
Lifetime Gold Member
Feb 12, 2011
atlanta, ga
looking pretty good. The backlash number is like the "BIBLE" for old gears!
Only thing I notice is your coast pattern went from originally "toe" heavy to NOW= heel heavy? That could be as simple as HOW YOU TOOK the pattern? rotating axle??? or using the pinion???..using the ring gear to drive the pinion??/ adding drag with your hand on the ring gear....etc. But used gears NEVER give you back the "pretty" pattern on a new set-up.

Last edited:

big gear head

Veteran Member
Jul 30, 2001
No additive for the Truetrac, just a good gear oil. I've got a few questions. Did you make sure that the bearings were fully seated on the new differential? I use a .001 feeler gauge to check the back side to see if the bearing seated completely. If it didn't then the bearing will move after you use it a while and that will screw up the backlash and bearing preload. When you shimmed it, did you get it tight enough that you could now pull it out by hand? Id you could pull it out the it isn't tight enough. It should be tight enough that you have to pry it out. In your case I would have gone for slightly tighter backlash instead of more loose. .010 would probably be better than .013.


Sep 9, 2018
Powell River BC
Righton Holland thanks, good to know no additive or break in needed, should simplify things.

Fbird, thanks for the diagram I'll save that, you're right I think I was pushing on the ring and turning this time rather than using the yoke and adding drag. I will try it again when I get a chance. Seems strange that the coast pattern does not seem to mirror the drive like in the diagram.

Gear Head, I haven't checked the back of the bearings, I can do that when I get a chance before I button it up. The carrier is definitely tight in there I made a tool out of aluminum and used it to tap in the passenger shims the last time I put it together. I was prepared to add the .003 shims to either side like you suggested but figured it was tight enough.

I actually had it set up with right around .10 but changed it to make it looser. I did write it all down so it'd be easy to switch it back, good to know.

Would be nice to be able to test drive it, should have the car running in a few weeks hopefully.

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