Im changing 80w/90 mobile 1 rear differental for my 92 pontiac firebird, just wonder how many quart do i need ? and do I need add fiction mod addictive on it ? thanks

correct me if im wrong but i think its 2 quarts thats how much i put in my 7.5'' rear and it filled it right up to the top. and you dont need anything but the oil if its a open diff. if its a posi or something youll need a special additive.

yeah your correct. it took me 2 quarts plus the additive for my posi rearend. I have the factory GM 10 bolt with posi and it only took 2 quarts and additive to fill it.

i just put a posi in mine...i have 80w90 but i didnt know about an addditive..whats it called? any specific brands? thanks

trans x i think is what it was called. the additive protects the posi clutches, cleans them and makes it so you can do posi burnouts. otherwise if you dont add the additive, you will burn up your rear end and only do 1 wheel peels.

with full synthetic rear end fluid i dont think you need the additive though.

How I know if i have pos ?

do a burnout and if you get 2 black lines, you have posi. what year and model is you car. My rearend was a 9 bolt but was swapped out by the previous owner for a 4th gen 10 bolt.
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i dont think you need to either because i know some come with it already mixed into the solution. But id still run th additive just to be safe if it was my car... better safe then sorry

1992 pontiac firebird v6 auto, but im doing v8 carb swap now.

most likely just a open diff. so no posi. probably have a 9 bolt underneath

wait i just swapped a 9 bolt in mines, it came from another 3rd gen its got disc brakes and higher gears, when i pop off the diff cover is there a way to tell?

any one here using, redline heavy shock proof gear oils on rear diff ? I still have 2 brand new quart ( from my other awd turbo eclipse gsx, I been use it on my awd rear diff with no problem ). just wonder I can use it here.

did it come from an auto or manual 3 gen?

I have no idea, but im assuming that since it came with disc brakes and its a full posi it came with 3.23's?? its also a 9 bolt, i have no idea what application this thing came out of. its got iron calipers so its pre 88 to 82.

yes you have posi because i was given the original 9 bolt to my car which has 3.23's in it. I then sold it to a friend of mine for his s 10 and he ran it at the track and it would pull posi until the fluid got dirty then only 1 wheel peels.

and how often did it do that to him? but as soon as he cleaned it, it went back to full posi right? i wanna make sure my fluids are always good to go back there so i can keep my 2 wheel peel.

I don't think 9 bolts never came with 3.23, they are 3.27's.

Take off the cover and look for the numbers stamped on the gears.41.15=2.73,40.13=3.08,42.13=3.23,41.12=3.42,41.11=3.73.

Limited Slip additive is what you need. And if you put it in a non-posi rear end, it won't hurt it. You can get it at any parts store. It keeps the posi clutches lubed so they don't chatter or grab and wear out.

There really is no certian mileage when your suppose to change your rear diff. fluid its really just up to you when you want to replace it. I just changed mine a few weeks ago because in reverse i could hear the clutches chattering.
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yes my mistake, they do have 3.27's.