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8 3/4 Diff Gear Lube

Posted By: markfh52

8 3/4 Diff Gear Lube - 10/25/14 04:13 AM

What gear lube would be best for the 8 3/4 posi diff. I know there's a limited slip additive that needs to be used but I was checking out Castrol 75w-90 synthetic limited slip lube. Can that be used or is there a better alternative. Thanks
Posted By: ademon

Re: 8 3/4 Diff Gear Lube - 10/25/14 04:20 AM

I'm going to use Torco 85w-140w racing regular dyno. with a bottle of the ford juice. It's on it's way from amazon.
Posted By: ahy

Re: 8 3/4 Diff Gear Lube - 10/25/14 04:59 AM

90 weight or 80W90 will work fine for general use. I have always used the parts store LS additive in mine (GM spec?) without issue.

Synthetic can help with temperature extremes: for really cold weather or if running sustained high speed/high temp. An xx/140 dino oil can help somewhat with high temps as well.
Posted By: GTSDart340

Re: 8 3/4 Diff Gear Lube - 10/25/14 05:00 AM

I just had mine give through this year. I put 80-90 in it with the LS additive. No issues so far!
Posted By: Pacnorthcuda

Re: 8 3/4 Diff Gear Lube - 10/25/14 05:05 AM

Quote:

What gear lube would be best for the 8 3/4 posi diff. I know there's a limited slip additive that needs to be used but I was checking out Castrol 75w-90 synthetic limited slip lube. Can that be used or is there a better alternative. Thanks



Your choice would be fine. For the additive go to a Ford dealer and buy it, it's the original formula MOPAR used to use.
If your ""posi"" is a cone type the additive you choose really doesn't matter, if it's a power lock clutch unit you want to feed it the best.
Posted By: mopowers

Re: 8 3/4 Diff Gear Lube - 10/25/14 06:08 PM

No need for the additive if the gear oil is made for limited slip diffs. That mean there is additive already in the oil.
Posted By: DoctorDiff

Re: 8 3/4 Diff Gear Lube - 10/27/14 01:04 AM

Regardless of what the label says, you must always add friction modifier to a bottle of gear lube.
Posted By: markfh52

Re: 8 3/4 Diff Gear Lube - 10/28/14 02:07 AM

So if I use Castrol Syntrax Limited Slip 75W-90 I should also use something like Champion Limited Slip Differential Axle additive concentrate or like the Ford additive as suggested.
Posted By: DoctorDiff

Re: 8 3/4 Diff Gear Lube - 10/28/14 04:13 AM

Yes, use the Ford additive.

If you can't smell friction modifier in the gear lube, it is either not there, or there isn't enough mixed in.
Posted By: GTX MATT

Re: 8 3/4 Diff Gear Lube - 10/28/14 04:19 AM

Quote:

Regardless of what the label says, you must always add friction modifier to a bottle of gear lube.



Even the stuff from Richmond?
Posted By: ademon

Re: 8 3/4 Diff Gear Lube - 10/28/14 04:54 AM

I just picked up the ford additive it's 4 oz and was about $6.50 from the dealer. I haven't sniffed it yet I'll report back on the smell in a few days.
Posted By: ademon

Re: 8 3/4 Diff Gear Lube - 10/28/14 08:32 PM

Ya it smells nasty. way more smelly than the stuff i got from NAPA that they have on the shelf. Always got a bit of popping on my truck 9 1/4 rear when i make a turn on a incline, well see if the ford stuff works better.
Posted By: Copper Dart

Re: 8 3/4 Diff Gear Lube - 10/31/14 06:01 PM

IIRC. Someone mentioned that it's made from whale blubber.
If true, that should explain the wonderful aroma! Eskimos use it as cologne. Yummmmm.nb
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