I have to replace an axle seal on my truck. I pulled the diff cover off to release the axle. I noticed that it says to use only 75W 140 synthetic oil. I was told that any synthetic will work. If I cannot find this oil will another synthetic work?

 

It needs to be the right weight since that is what designates its viscosity at given temperatures. Ford is the main place that will carry it. Its not a widely used oil. Amsoil I think makes a 75W140, but around here at least you have to order it. I just went to Ford and got the oil. Sucky thing is that due to the weight of the oil and the fact that its full synthetic its about $12-14/quart. It sucks, but if you don't use the right oil you get to pay for an axle rebuild. They recommend that specific fluid for a reason.

 

I just replaced my diff oil in the rear trying to get rid of Trac Lok chattering on the turns. No auto parts store had the stuff. They had 75-90 but not the specified75-140 synthetic. I had to buy it from the dealer. They charged me $13 per qt. and that was supposedly at a discount!!!!! It didn't get rid of the chatter. There is a TSB out that says the clutch pack needs to be replaced with less shimming to get rid of the problem.

 

Suprisingly enough I just found 3 qts at Checker Auto Parts. It is Mobil1 and I paid $15.00 a qt. I think an Engineer at Ford is benefiting from oil sales.

 

Hey guys...I had the same problem with the chattering in the rear end. I learned from this website to use a container of "Friction Modifier". I bought the stuff at Advance Auto Parts in Indpls. $4.50 I think was the cost. I added to the Diff. Not an immediate improvement. It took about 750 miles before I noticed the problem is gone. No chattering. I guess the stuff has to blend with the synthetic fluid to get results.

DaWG

 

I just changed my rear axle fluid and did a lot of research on it and here's what I found, I went with the Royal Purple.

Ford - $17.95 (Nearest Ford dealer)
Mobile1 - $15.95 Auto Zone
AMSOIL - $12.05 (Online at http://intershop.amsoil.com)
Royal Purple - $7.97 (Online at http://www.rpmoil.com)

 

I changed mine & ford said they are putting in 75w 90 inall their posi for oil changes , its supposed to be better.

 

SORRY, THATS 75W 90 SYNTHETIC!

 

Hey thanx for the pricing info. wanting to change gear eventually and was gonna go with amsoil. definitely gonna use royal purple now!

 

There is a tag on the rear cover that says use only 75-140 synthetic! Unless there is a TSB on this recommendation, I would not believe the dealer service department.