The original 9 bolt went out, (started to peg-leg) so I swapped it out for another.

I'm like 99% sure that all 9 bolts takes ATF, but when I pulled my cover, there was really really thick gear oil. I pulled the 9 bolt out of another thirdgen ('89), and don't know how long it's had the gear oil in there, but I had it in my other bird ('82), but I only drove it with that rear for probably less than 500 miles.

I should refill it with ATF right? And at work we use brakleen to clean out the rears when doing a diff service. Will brakleen hurt the clutches in the rear if they aren't already messed up? And what about additives? Any one use them? I read on the back of one it said not to use it with ATF.

BTW, both tags were still on the rear end.

 

I would not put ATF in the rear,,,even the 9 bolt. I have a 9 bolt in my iroc, the cover had never been off the car with 50,000 miles on it. I changed the grease recently, it had gear oil in it, as it should. ATF will not work, atleast for very long put gear oil in for sure. I didn't use any posi additives in mine since it is very quiet turning corners anyway, it works very well so a simple grease change is all I did. Hope this helps, Larry.

 

ATF will not meet the extreme pressure requirements of a hypoid gearset in a rearend. Use 75w90 gear oil or the like. Also, with a factory clutch type posi I always add the GM limited slip addative. Soem gear oil is formulated for use in limited slip rears, and theoretically shouldn't need the addative, but I always add it to be safe. I'm not sure about the 9-bolt though, because it uses cones instead of plates and clutches.

 

Dont use the additive since the 9 bolt is not a clutch type posi. it requires friction to grip. NOW if it makes noise then you may need the additive to quiet that down, but I've never used it in my 9 bolt.