I did a search but did not find a good answer.

I am going to change my gear lube and need some opinions on what brand to buy. I am leaning towards Redline or Royal Purple but would consider other brands. I am giong to get 75W90 not the 75W140 that is stamped on the axle. I am running RP 5W20 motor oil and would like to stay with them for the lube, but it looks like Redline is better am I correct or does it really matter.

Jeff

 

If you searched, what you found was nothing but opinions. And all you will get here is more of the same.

All oil topics have responses like "I have used brand X for 100,000 miles with no problems." Fill in the blank for any oil.

There is no clear winner. Hell, there's not even agreement on what weight to use. Same with friction modifier.

Bottom line: They all work. Mobil 1, Redline, RP, who cares? I would not hesitate to put any national brand synthetic in my diff.

 

You are correct there is no clear answer on brand, weight, etc. Just thought I take a stab in the dark.

 

except you better have a frition modifier, you can call and ask for most oils if its already in the oil, if not ford sells it for about 4 bucks i believe.

 

I changed mine out with Mobile 1 80w90 and no friction modifier. About 2k miles so far and it is not popping around corners yet; which my rear has well over 300 passes at the track

 

The Ford 75W140 is synthetic so why not use it. It was a no brainer for me to go back with it.

 

just word of mouth but . . .
i heard the syn oil has some problems with inability to absorb moisture which can lead to early wear on parts. I don't know for sure, just what i've heard.

 

Correct me if I am wrong, but don't our rear ends have vents? I know mine has a hose the goes up and connects to the bottom of the bed.

 

yes they do

 

Oh, yeah. Mine has puked oil all over the crossmember that it plugs into.

But I bought a solution (I hope):