turo

i have a 1985 z28,305,tpi,at.trans,the #s on my rear axle read 91bc1912, i can,t find these #,s in any codes. can someone tell me what type and gear ratio axle i have, oh it;s a 10 bolt. thanks. i emptied the fluid and need to know what type of fluid to use.

AlkyIROC

Those numbers mean nothing to me. Are they from the front of the right axle tube? They should be something like 8JB C 191 2. It's the 91B that I have no idea on. C = Made in Buffalo. 191 = Day of year. 2 = Night shift

1985 z28,305,tpi,AT came with 3.23 gears only. No other gear options for that specific model from the factory.

Fill the diff with 80w90 gear oil or 75w90 synthetic gear oil.

------------------
Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress

Best results before the 383 blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car
91 454SS daily driver
95 Homebuilt Harley

JERRYWHO

This is on the auburn website

What kind of oil should be used with an Auburn differential?
It is important when installing Auburn differentials that a high quality, non-synthetic 80w90 GL-5 oil, treated with GM or Ford limited-slip additive (also known as friction modifier) be used. Three ounces of additive will treat one quart of oil.

Note: auburn spec is non-synthetic only if you use synthetic type oil in the diff the posi will slip more.