Front/Rear Diff and T-case Oil?

kylant1 · #1 (**permalink**) 02-11-2005, 11:16 AM

I'm getting ready to change the diff oil and t-case oil in my truck. The manual says to use 75w-90 Hypoid gear oil in the front, 90w gear oil in the rear with limited slip, and 75w-90 gear oil (doesn't mention hypoid) in the t-case.

I was wondering if it would be okay/acceptable to run Mobil 1 synthetic 75w-90 gear oil in all of these spots? I don't see why not. It meets all the spec except is multiweight and the rear diff only calls for a 80w-90 multiweight when used below 0*.

thanks for the help

KLS · #2 (**permalink**) 02-11-2005, 12:37 PM

Many of use have run syn 75W-90 in the rear with good results.

Ken

naunibecker55 · #3 (**permalink**) 02-11-2005, 02:35 PM

Dealer also uses 75w90 synthetic.

HotRod8 · #4 (**permalink**) 02-11-2005, 08:54 PM

Are you guys sure this okay, I mean using 75W-90 instead of 80W-90? I know that Ken is very well informed on such subjects so I will certainly respect his opinion.

The spec. in my manual for the rear diff. is SAE 90 (above -18*C or 0*F) or SAE 80W or 80W-90 (below -18*C or 0*F). What does this mean? Up here in the "Great White North" we routinely see -18*C during the winter, but certainly not constantly. About 2 or 3 weeks ago it was something like -30*C (or about -22*F), but for the past week or so the highs during the day have been +10*C (50*F) or better. By next week we could very likely be back to that -30*C sh$@, I mean stuff. What are we supposed to do change our gear lube every week?

I do know that 80W-90 gear lube is not easy to find, I ended up buying Amsoil as that was the only brand I could find in that weight. I really like the idea of just buying the 75W-90 and using it in both diffs and the T-case.

Rod

KLS · #5 (**permalink**) 02-12-2005, 11:03 PM

I installed Amsoil 75W-90 shortly after I bought the truck. @ 60,000 miles I drained the differential to install a limited slip. The Amsoil gear oil came out bright green just like it went in. The gears had very good looking contact patches--no fretting, no wear evident at all except for normal contact. The magnet on the drain plug had little or no steel on it. Part of that mileage was towing a 5200# trailer in 90 & 100° weather at highway speeds. I put Schaeffer 80W-90 back into the differential because it is an even heavier duty gear oil. I'd feel OK about putting Amsoil back in, though.

Ken

kylant1 · #6 (**permalink**) 02-13-2005, 10:52 AM

what about the transfer case? i'm pretty sure I will use 75w-90 in the diffs.

KLS · #7 (**permalink**) 02-13-2005, 01:19 PM

75W-90 in the front diff & t-case, preferably syn. 80W-90 or 90 wt. in the rear diff, but synthetic 75W-90 works very well.

Ken