Differential Fluid?

[Timbo]

Just wondering what kind (brand name) and weight and how much of differential fluid everyone else is useing in there 9 inch ford 31 spline (narrowed about 9 and a half inches) rearend differentials?

[Anthony]

The best diif fluid is probably the synthetic stuff. I use Mobil 1 gear lube, something like 75w-90. Redline makes a synthetic gear lube as with some other companies. Even though it is for use in limited slip diff's, I was starting to get some clunking, so I had to add some of the limited diff additive as well.

You fill it up to the level of the fill plug, half way up the diff housing.

[Jack21]

Mobile 1 synthetic diff oil with a bottle of Ford friction modifier added for the posi. Fill to the bottom of the fill plug.

[SCOBRAC]

Mobile 1 or other good synthetic for an open differential. FYI I used it in my 20k mile salisbury and it made noise. I now use 90wt Valvoline designed for posi / powr loc units.

[BMK]

Yes use the Valvoline also. A small ratchet fits nicely in the drain plug to assist with removal. Front drivers/left side Don't overfill.

Cheers

Bernie