Posi Gear Oil

[Taylor1969]

Hey Guys...

What gear oil should I be running in my 8.5" Posi? I put synthetic oil in it and when it warms up it seems to make a little noise when taking corners.

Should I be putting in conventional fluid w/ GM additive? If so, what weight?

Thanks,
Chris

[megaladon6]

redline makes a "shock proof" gear oil or something like that in 2 grades-light and heavy. i knew a few people with noise problems that switched to that and it worked great. it's a synthetic too.

[zman1969]

sounds like a good working posi unit, may try the additive - cant hurt but the clutches in a 8.5 (72-87) are all metal so it may not help you can take the unit apart and take some of the shim out of it if you want - if it were me I'd leave alone

[chicane67]

If you are using a late model EATON posi... you shouldnt use a synthetic.

If you are using a steel plate clutch pack, like that found in the OE posi... you can. However... I dont recommend using a synthetic in the differential at all. I would look for a good parafin base oil like that from Schaffers (#209 moly) or TORCO (RGO 85-140.)

For your climate, you can run a multi viscosity 85-140, or either a straight weight 90 or straight weight 140.

At this point... all you need to do is add about four ounces of friction modifier to the base oil that you are currently running. It can be had from your local GM parts dealer or your local Ford parts dealer.

[Taylor1969]

awesome guys! thanks for the help. I'll get some friction modifier and see how it goes - I would use the Type G right?

It is an OE unit. I have never had a posi on an older car and didn't know that they made a little bit of noise :D

I am going to go ahead and order

2 bottles of the Type G
http://www.torcousa.com/products/productview.aspx?id=1914283f-d2ed-4b16-aba1-2a23959bab02

and four bottles of the 85-140 Lube
http://www.torcousa.com/products/productview.aspx?id=d5d2bd7a-2331-4720-91c5-cb92901bda83

should be enough for 2 Changes :wrc:

[minendrews68]

Hey Chi, what do you do for a living? You seem to be pretty knowledgable about a lot of things. It has to be some sort of Mech Eng. ok don't start getting the big head and all. lol

Carl

[64Chevelle]

I'm trying LucasOil 85W-140 heavy duty in my OEM 8.5", it's got the LSD additives in it already so I won't have to worry about getting the right amount in. Any experiences with LucasOil here?

[Taylor1969]

The Torco stuff mentioned above works like a charm. No more noise and no leaks like i had with the synthetics!

[JEFFTATE]

Where did you buy the Torco ??

[ErikLS2]

FWIW, I just ordered some stuff to o/haul my 12 bolt from Drivetrain Specailists and asked them about synthetic oil. They claim to have run a test on synthetic vs. conventional gear oils and while the synthetic oil itself was cooler than the conventional oil the gears ran hotter, when the conventional oil was used the actual gears themselves were 20-30 degrees cooler.

[Taylor1969]

Where did you buy the Torco ??

Directly from Torco in the links above

[big gear head]

I've run Amsoil Severe Gear 75W90 in 100 or more Posi rear ends with no problems. Most synthetic gear oils will need the GM oil additive.

[MonzaRacer]

Only issue with synthetics are that you cant run synthetics where water is an awesome.
Now as for never running synthetics in rearends, thats bulls--t. I have built hundreds and never had any issues. NOW if the actual center section calls for non synthetic but have never seen any documentation yet leaning that way. Again I have built hundreds of rearends and had no issues, now I will say that in heavy duty use stay away from Valvoline gear oils, had several big trucksthat lost rear gears with it.
Lee Abel
AFTERMARKET PERFORMANCE