: Rear Diff Question

08-11-11, 02:25 AM
Will using 75W90 full synthetic gear lube in the 8.5 inch rear axle be okay or no? Will it help increase fuel economy and wear vs the 80W90 lube?

I had to replace my rear axle seal and wheel bearing the other day for my 94 FWB. The problem is, my axle shaft has worn a groove on the shaft, but I used a axle repair bearing for now to help me get by until I can find a new or used axle shaft. I was just wondering if using a lighter oil will help with wear and or cause possible leakage.

I heard Timken axle repair bearings being crap and leak out right away, I used National Bearings, and so far it's been fine.

08-11-11, 09:52 AM
Synthetic is always a good choice, but that 75w90 will be the exact same viscosity as the 80w90 when you are driving. Remember, the first number is the "W"inter viscosity. I would go with a good 80W90 synthetic, but only after you change the axle. Fill it with cheap stuff for now since you will be draining it again ;)

08-11-11, 01:15 PM
I used 75/90 synthetic in my 8.5 last year and I've had no issues with it. I haven't opened it up again but there is no noise and the tires spin nice and smooth when its off the ground but I don't think you'd notice a difference between the two.

08-11-11, 03:59 PM
yea the axle curse someone had a set on here a while back i still need a set sucks because theirs no aftermarket, dealer wanted 350$ no studs ,or reluctor :crying:

08-11-11, 09:02 PM
Great, that's good to know guys. Once I replace the axle, I'm going with 75W90.

08-11-11, 10:19 PM
those axles sell as quick as I get them
I do have a set now but 1 is spoken for
and Im not ready to render the parts car inoperable
just yet, maybe another month......

08-12-11, 03:23 AM
Once you decide to sell them, let me know ASAP Jim. I just need one, right rear.

08-12-11, 05:35 PM
i need a axle too the dealer told me they are discontinued andi cant find one anywhere. i'm thinking about swapping the rear end out for one with disc breaks.does anybody know if the rear end out of a impala ss or a newer brougham will fit under a 90 brougham?

08-12-11, 09:04 PM
I don't think we can use Impala or even Roadmaster axles, I heard someone say that the Fleetwood and Brougham axles are uniquely specific to our cars which really really sucks.:nono::helpless:

08-12-11, 10:46 PM
I have the Caprice axle on my 90 with disc brakes. From what I understand, you can fit Impala, Caprice, 9C1 Caprice and Roadmaster axles under the 77-79 caddy. The wagon rears dont work for some reason(anybody know?). Great upgrade for 77-89 caddys because you get an 8.5" rear end and 3.08 gears. 90-92 w/sbc Caddys already have 8.5" rears but with gears around 2.73. Some rears are wider than others but they should fit. Look for the Impala or 9C1 if you want disc brakes.

08-13-11, 05:09 AM
i found some axles on ebay one posting gave the dimensions and spline teeth count and it matched mine so i'm going to try it and let you know if it works this is the listing Cadillac RWD Rear Axle Shaft 8.5" RH/LH 91-92