I have a 10 bolt 3.42 limited slip disk brake rear end from a 93-97 F body. I want to service the rear before I install it in the car and when I went to the auto store they had so many different weights for rear end fluid.

So lets say I planned to run regular rear end gear oil whats the recommended weight?

What if I went with synthetic, what weight would I run?

 

80W90 wt.

I used the Valvoline Syn, about $8/qt.


Ed

 

Gm requires that you use a limited slip addiative. I changed my fluid and didint add any, only to have this chattering noise come from the rear. Its something like $20 for a 7 oz. tube from GM.

 

alota people have been saying this (about the chattering in the rear end) but i havent heard a single noise comeing out of my rear axel since(and before) i changed my fluid. i used valvoline's non synthetic cheap *** brand and i havent had any problems. i never used GM's anti friction additive either. how/when does your rear end chatter? i dont rat bag my car around all the time or anything, i just calmly drive to work and back without any problems or noises. but on the other hand, i do have a 9 bolt.... i hear 10 bolts suck, mabey thats why? i usualy dont go cheap on my car when it comes to fluids, but it was 3 - 4 times more expensive than the non synthetic and i just couldnt justify spending that much money on oil.

 

$7 per bottle at the dealer.


Ed

 

I had mine changed and didn't put the additive in and it started making noise. Changed it again and put in Redline synthetic and the noise went away.

 

For regular non synthetic, 80-90 is what I see recommended the most. I'm running this weight along with the friction additive in my eaton posi rear and it works great.

 

i've used 75w-90 M1 in a lot of rears with no problems, used amsoil in a few too with no problems. i'd only buy the gm posi additive, cost me around 5 dollars a bottle, but i get a price break.

 

Well I know always use the GM friction modifier with the posi units, which I have been doing anyway.

Now I know exactly which synthetic or non synthetic fluids you guys are saying to use, which is totally fine with me. My question is whats the difference in those numbers? Is it rated like oil where in colder climates you want a thiner oil? Or is it that certain types of rears just need a certain rated oil? So like what is a 90W140 used for? I'm just curious.

Thanks

 

Hmm... is it me or don't you have a torsen posi unit? I thought all 4th gen's came with the torsen. If that's the case, you don't need any additive, just gear oil. The torsen isn't a clutch type limited slip. It uses the angle of the worm gears for friction in distributing torque to the wheel with grip.
I'd go with 80 weight. If you change it every 30k miles you'll be fine. If you can afford it go with amsoil and never change the fluid . Does that last statement make me sound like I love amsoil? Well I DO! Although I use the cheap stuff to give me an excuse to open things up for visual inspections .

 

I asked a trans mechanic what the deal is with the different weights once a long time ago. I was curious about running the heavier gear oil in my muncie four speed. He said the heavier weight oil can actually cause damage to the bearings and other parts because since it's thicker it doesn't creep up the gears and get distributed very quickly, which made sense to me. I've actually heard of a couple of guys that trashed their manual trans or their rearend from using the heavy weight fluid. I think that stuff is probably best suited for farm vehicles and maybe semis because I would think that it probably absorbs shock loads to gear teeth better than the thinner stuff. Just my .02.

 

i use redline synthetic 140 wt , it will quiet the gears just a touch more than 90 wt regular oil. but you really have to listen to notice a difference.