I'm going to change the gear oil in both my '93 F250 4x4 differentials.

The rear is a 10.25" which calls for 3.5 quarts of 75W-140 synthetic, so that's what I'll use.

The front is a D50 and the spec is 2 qt of 80W-90. Is there a good reason to use 75W-90 synthetic, or just stick to what the factory originally specified?

thanks
Charles

 

 

Yes, thanks, I have seen that chart but what exactly is "4x4 Gear Oil"? I'll have to check and see if my front diff is open or limited-slip. I know the rear is (Axle C5).

What I want to know is, can I run 75W90 or not?