i changed my rear end fluid about 500 miles ago from dino to synthetic. i purchased a new gasket torqued the bolts down and i noticed a minor leak a week or so later. so i drove the car for a couple weeks with the minor leak and i just decided to buy a new girdle. so i got the new girdle and installed it. this time i used rtv along with a gasket. however, when i changed my fluid, i noticed it was totally black. this fluid was only in there for 500 miles. i did not know what the deal was. the only thing i can think of is that the synthetic is cleaning out the the rear. any suggestions?

 

I had synthetic but went back to the other stuff after the rear end kept making noise. Noise went away with the "dino" stuff. As far as the oil being black, mine looked ok when I switched back. "Dirty" but not black.

 

I'm not sure why your gear oil got so black, but FWIW, I changed to Mobil 1 synthetic for the axle probably 40K miles ago, and have had no trouble. I change it every 10K or so. I've found you MUST use the GM additive to avoid noise from the diff, even with synthetic.

I always scrape gasket surfaces well, use a new felpro gasket w/o RTV, torque the bolts to spec, and have had no leaks.

-Chris

 

what's the felpro gasket part#??????/ thanks

 

RDS55072 for the fel-pro gasket.

 

Yep i second scraping the old gasket really well and using the felpro one.
I used RTV in the past and didnt clean the surface too well and had a leak a few months later. Ripped it all off and did it right, bought some gasket remover to get rid of the old gasket stuff and had the mating surfaces perfectly clean.
I used 75W synth for the diff tho and the GM additive. It still has a slight whine to it but barealy noticeable... I might swap in the dyno stuff later *shrug*..

 

I use synthetic, no problems no leaks. I use some WD-40 to clean out the axle housing, and a few clean rags. There is always a bit of sludge at the bottom, if you dont get it out, the new oil will just stir it back up. Make sure to clean off the magnet in the diff cover, that way you can get an idea of how much wear is happening between oil changes.

I've never had good luck with diff. cover gaskets. They always seem to leak, regardless of what I do. I use RTV only, and clean both surfaces with carb cleaner. So far, so good.

 

i was scared to clean the inside of the differential out because i have heard of problems after doing this. i now have my TA performance differential on so i have a drain plug. however, they don't come with a magnet inside. my differential is still dirty inside. i can see it in there. its all coated with black crap. i think i will just put a few hundred miles on it and change it again. i may have to do this a few times to clean it all out. it may get a little expensive but i will get it cleaned out anyways. i also always use the gm limited slip additive every time and i don't have any whines that i can hear.