Looking to see what brand of gear oil people use in their rear diffs and manual trannys. I have an 87 GL Wagon and am about to switch out my oil. I just wanted to see what people thought was a good brand of oil. Thanks for the input.

I was wondering if I could use Valvolines Full Synthetic 75/90 Gear Oil in the diff and manual tranny or would that cause problems with slippage. Am I better off just going with Valvolines High Performance 75/90? Any suggestions would be much appreciated.

i use full synthetic in my rear diffs, manual trans, front diffs. others here do as well. i asked a dealer, Subaru dealer in atlanta uses Pennzoil full synthetic, they even sold it there when i stopped in a few years ago. or at least they were going to sell me a bottle (it was very expensive, so i got it elsewhere). i use valvoline just because. Synpower i believe it's called. no problems here.

Thanks grossgray. What are other peoples feelings on going full synthetic? Anyone experience problems with slippage?

don't see how the diffs could slip in a manual trans. either the gears are working or they are not. start loosing teeth on your gears and they won't slip, it'll be really noisey.

 

i have an LSD and use full synthetic in that as well. are you concerned about something in particular because this is a very basic question. if you drain oil, replace it. brand new synthetic can't be wose than the decades old 100's of thousands of mile stuff in there now.

 

if you're really concerned about it, use regular fluids they won't cause any problems either.

I believe your question is answered, so is it okay if I hijack your topic a bit

 

I find the manual trans on my '88 xt turbo not a very smooth shifter, it has only 80k miles or so on it, so maybe I use the wrong oil?

 

I don't know what is in it ATM but what should I replace it with? so my gearbox will shift nice and smooth again instead of this rough stuff.

 

thanks, Joost

have you checked the gear oil in it? check quantity and see what it looks like? just changing it/filling it up may help some. might want to do a search, i've read other threads about people smoothing out shifting with different gear oils/additives.