alex722607

iTrader: (3)

Hello all,
I have 1988 Trans am GTA, with a 9 bolt and it's an ls1 swap. I recently noticed that the differential is leaking fluid and I need to finally change the seal. The car essentially sat for a long time and the diff was never opened up from its awakening to the swap. I know nothing about changing the fluid in it, although I've seen my dad open up the 10-bolt on his old 2002 T/A. What specifically should I know going into this. I read some of the stickies but as far as the simple things I would like alittle guidance.

How should I go about draining and refilling? Being that the oil is probably 20+ years old what should I be on the look out for color wise. (besides metal shavings). I hear nothing strange back there, it seems quiet. Is it really as simple as draining it cleaning the mating surface for the seal and installing a new seal?

big gear head

Which seal is leaking? You have to remove the cover to drain it. There is a rubber plug in the cover that is used for refilling it. This plug usually leaks a little. I smear a little RTV sealant around the plug before pushing it back in the hole. This seems to help some.


The oil is probably going to be black, or close to it. Powdered metal in the oil is normal for this rear end due to the cone type differential, so don't be alarmed when you see it.

alex722607

iTrader: (3)

The big seal... The one that seals the cover

big gear head

OK, that's a gasket, not really a seal. Many people don't use a gasket when they put the cover back on. They just use RTV sealer on it and stick it on. If you do this be careful that you don't use too much. It will squeeze inside the housing and eventually break off and get into the bearings.

alex722607

iTrader: (3)

Haha, I have a gasket lieing around somewhere for it. Actually bought it last year with the intention of doing it then. That spot ilunder the cover was always a little damp, but now it's a full on drip.

When I go about refilling it, how do I go about that. Do I have to use some sort of pump, or does the 75w 90 bottle fit underneath the car.

Another question for the 9 bolt is does anyone know exactly how much is supposed to go in

Thanks a lot

big gear head

Don't know how much room you have under there. but the bottle might fit. Usually 2 quarts.

alex722607

iTrader: (3)

Got all the old fluid out, cleaned the mating surfaces, installed to cover and gasket with a little adhesive. Filled until fluid started coming out from the fill hole. I think about 60 ounces went in. No leaks now.

As far as why it started leaking in the first place, some of the bolts became loose - finger loose. So upon reassembly i made sure I coated it in lock-tite (actually a permatex version of it)

Haven't driven it yet, as immediately after I decided to do the struts too.

big gear head

The bolts may have come loose because the old gasket decayed and compressed.