I am changing the fluid in the rear differential.
How much gear lube does it hold?
If I cant find a full synthetic will a synthetic blend work?

 

My 2000 4x4 uses just over 4 quarts of the 75-140 and a pint of the ford friction modifier. The only other company that makes the 75-140 that I can find is royal purple. I don't think anything but full synthetic would be a wise choice, especially since it's fully synthetic stock. Good luck.

 

Redline also makes 75-140 full synthetic, which is what I'm running in the rear diff. I'm also running Redline fluid in my 6 speed.

Terry

 

Amsoil too. Got it in both diffs, tranny and transfer case.

 

You don't really have to "measure" because you're supposed to fill it to the bottom of the fill hole for the Sterling 10.25" and 10.5". Buy 5 quarts and if you have any left return it. I would recommend synthetic and not a blend since it stays in there for so long. I'm assuming you're removing the diff cover. That seems to be the only way to get ALL the old stuff out.

 

And since it rolled off the assembly line with full synthetic in it, it would be a step backwards to use anything else.

 

Mine had a tag on it which stated synthetic only! I put in the amsoil and it took 3.3L or just about 4 Qts.