What type of Gear Oil???????

[Crankshaft]

Hi I have a 1972 Duster currently with 3.91's and am switching to 4.30's what gear oil would be the best. I'm also installng a detroit locker, and want to make sure I'm giving everything the best lubrication it can get! Also should I use posi lube?

Also with the 3.91's I ran through the traps at 5300 rpm on a 25" tall street tire. What can I expect my rpm to be with the same tire but with the 4.30's. I'm running a 727 auto.

Thanx for all the help.

Crankshaft

[69MOPR]

I think 70W90 is the recommended weight.

If you go with a synthetic, you may not need to add a friction modifier. The synthetics are so slippery, that your sure-grip may slip too much with the modifier. If you find the rear popping or grinding around turns, so can always add some friction modifier later.

If you go with a non-synthetic, you will need a friction modifier.

I just install a new 3rd member and put in straight Red Line synthetic. Haven't had a chance to test it yet.

Oops. Just re-read and noticed you are using a locker. You should not need the friction modifier.

[71chargerse]

i use amsoil in my 8/3/4 and didnt add the modifier and have had no problems for the last 2 years.

[Ausydad]

For a sure grip with higher gears ratio, I would recommend Valvoline 75w90 Durablend semi-synthetic. Also add the Equa-tork limited slip additive. You'll have plenty of protection and no worries about the synthetic eating your seals.

[JoeM29]

i have always used mopar gear oil with mopar posi additive is this good enough or should i use synthetic
thanks, joe

[warlockpowerwagon]

391 = 5300 rpm @ 100.9 mph 25 inch tall tire
430 = 5830 rpm @ 100.9 mph 25 inch tall tire