I have a 91 f150 with a regular differential (code 12) that uses 80w90, the manual calls for 5.5 pints of fluid. I bought 3 quarts and put almost all of them in and the level just barely made it to the plug. I drove it about 6 or 7 miles and started to hear a faint low roar coming from the rear end, is it possible to overfill it? I would think the plug would be at the full level or do I need to pull some of it out and go with the manufacturers recommendations? It could also all be in my head too. lol. But I do know some gearboxes are sensitive to level changes. Any ideas are welcome, thank you.

 

Its supposed to be 1/4 inch bellow the fill hole.

 

Only possible if you can screw the fill plug in before the gear oil flows out the fill hole, if you can touch the fluid with your finger through the fill hole you are good.

 

No, even with the hole.

 

Take the plug out, see if any fluid drips out. If it does, let it run out for a bit. Put your pinky finger in the hole and check the level. You can also jack up the right axel a bit to remove a bit more fluid. Does your truck call for friction modifier? If so, I hope you use it.

-Brutus

 

Everything I can find on it calls for straight 80w90... I can use the oil container with a clear plastic tube to suck some out. I've been running the same grade oil in it for 7 years, just don't ever remember having any questions about the level. I googled the differential code and it's apparently a regular rear end with no additional additives required. I'll look again though, maybe I missed something.

 

My specs show 1/4" to 9/16" below the hole, but I doubt even with the hole makes a difference so whatever.

 

Here you go:

 

This is what I see, but either way should make no difference.

 

There ya go Sean