I was going to put new fluid in the rear of my 71 ss chevelle. i noticed in my chilton book that up to 1971, it took 3.75 pts. to fill.
from 1972 and later they take 4.25 pts.
i was wondering what changed in the 1972 chevelle rear that it took extra fluid?
if you check the codes on the rear it will tell you what grears, where it was made, what day of the year it was made and if a posi or not.
nowhere does it give you a year. my car is not numbers matching so i really don`t know what year it is.

Bill,
Just fill it until it is at the bottom of the filler hole. Whatever it takes is what it needs.

Lubricant capacity:
1969-1971
Light duty axle...4.5 pints
Heavy duty axle...4.9 pints

1972
81/2" inch ring gear....4.25 pints
87/8" inch ring gear....5.4 pints graemlins/beers.gif

Sorry can't answer your question. But fill it on level ground until it leaks slightly from the filler/level hole. Also VERY important with 12 posi, you must add the GM posi traction additive that you can get thru you're local chevy dealer. It is about 2 fluid ounces and used to come in a red bottle. It is a special lubricant that you MUST use!

Also in addition to the GM posi fluid, I recommend using a good synthetic rear fluid like valvoline syntec. Less drag and no breakdown.

I have to question the assertion that you "must use" the GM additive for positraction. When my '65 w/12 bolt and Eaton Posi started winding-up and popping after sharp left turns at 90,000 miles, I simply drained it and refilled with Sta-Lube 90 weight GL-5 oil. No problem after that.

My $0.02

Is there a 10 bolt posi and if so does it need the special GM additive

Yes there is a 10 bolt version and yes it does need the additive.

JJ, I suspect you broke the friction plate and that is why it stopped making noise, any friction type locker (GM, Ford, and DCX all use them) need friction modifier.

PS, the older stuff doesn't smell too nice and really pisses guys off when you dump a little into their air tools fittings.....for a week evrytime they squeeze the trigger they get a blast of nasty stench.