On most of these questions about changing the differential fluid, I keep seeing instructions to refill the differential with fluid until it runs out of the hole. In my manual it says, on 9.25 axles, to fill the unit to within 5/8" of the hole. I have seen a TSB where possible damage can be caused to the axles due to over filling the differential. The problem arises when the fluid, when overfilled, can foam within the axles causing improper lubrication resulting in axle failure.

 

This is correct. You dont fill it up until it comes out but you can. It is really supposed to be a bit below the hole. Now I thought it was about 1/4" but it could be 5/8". Im not sure but I do know its supposed to be slightly below the fill hole.

 

Why can't I use 75-90 in the rear. Thats what my OM says.

 

You can but 75-140 for guys who use thier truck to tow things. So you might as well put it in.

 

So how much friction modifier am i supposed to put in, the hole bottle of any brand?

 

depends on which LSD you have but my Auburn requires 3oz per qt of oil

 

i have the stock one

 

A small 4oz bottle is what the manual specifies.
Don't forget to do several large figure of 8 turns so the additive gets well mixed up with the diff fluid.
I have a DTT and don't need this stuff now lol.
As for service interval, it's 15 thousand miles for the front and rear diffs on a 4x4.
These Dodges sure are heavy on the services, but I guess it's to "catch" those clutch pack retaining clips.
Al.