Background - After paying to have two places botch up my differential I'm doing it myself (I can't possibly do worse).

The problem - I have no idea what the original pinion shim was and I don't have the pinion depth gage.

My Method - The rearend assembly is in my basement so I have lots of light and room to work. I have honed out the two old pinion bearings so they slilde onto and off of the pinion easily. This allows me to quickly disassemble the pinion so I can try different shims. I've tried many shims and seem to need a shim around .015".

Question - Isn't this unusually thin for a pinion shim? What is the smallest shim anyone has run across? Can you get a good contact pattern with the pinion at an incorrect depth? Lastly, does anyone have the torque spec for a rearend support cover?

Thanks,

Scott

 

check this out. normal pinion shim size is around .030. You will probably never get correct contact with a .017 shim. If your car originally came with a 2.73 gear, you might as well buy a new carrier cause the gears you got aint gonna fit. I would start out with a .032 and go from there. Keep your backlash under .006 and make sure that you don't crush your sleeve more than twice. Your backlash is very important, as anyone else who works at a GM dealer will atest. F-bodies are very bad about whining. Please note that once you drive it there is no going back.

 

This is my 3rd 4.10 ring and pinion so it does fit (already have the ring gear on the carrier and the pinion in the housing).

Like I said, the correct pinion shim is .015 or slightly larger. When I tried a .030" shim the contact pattern was no where close to being correct.

My new ring gear is marked for .008" backlash. I'm shooting for that but don't have a dial indicator on it yet.

 

I think my pinion shim was .034, and it ended up with a little bit more pinion preload than normal, but not too much. I went with a backlash of .009 for my motive 4.10's. I wasnt comfortable with anything under 8. Good luck!
Brandon

 

When you tried the .030 where EXACTLY was your contact on the ring gear. Close to heal-toe, drive-coast. Also What ratio did your car come with originally? You mentioned that the other gears where botched, you may have a series 2 carrier and require a different chunk. I work at a chevy dealer and have access to all the measuring equipment available and have never measured pinion depth on a 7.5" under .027

 

Thanks for the replies...

With the .030" shim, the contact pattern on the drive side was toward the toe and heavy in the root. The pattern was close to the heal on the coast side. The instructions that I'm using state that I needed less shim in this condition. A .020" shim resulted in a slightly better contact pattern but it still wasn't perfect. Now I have a .0155" shim and the contact pattern is much better on both the drive and the coast side of the tooth. (Larger contact pattern on the drive side but still toward the toe, contact pattern on the coast side is toward the toe too).

Just going by pattern I'm very happy with what I'm seeing. My concern is how thin the shim is and if this is unusual.

Scott