Doing a gear swap and picked up some gear oil...75w140 synthetic. Now i'm having second thoughts. Should I have got the 75w90 synthetic which is closer to the original 80w90 Ford fill. BTW... I got friction modifier also. Any insight would be appreciated.

 

I would stick with the gear oil that is closer to the original ford fill.. I run the Moble 1 synthetic rear end gear oil at the weight of 75W90

 

75 140 will work but i would get it checked out first ..ive put it in many rear ends that call for 80w 90 but it is not always recomended ... u can run the friction modifier in either 75 90 or 75 140 .. call up the dealer and give em a quick check.. also what year is the car?

 

You will not have any problems with 75W 140. MPW/ Steeda recently changed my diff oil and installed 75w-140 Royal Purple and Ford Friction Modifier. No complaints from me. It is slightly quieter than the stock 75w-90 fluid. Its piece of mind knowing the RP is one of the better fluids available, especially if you have a heavy foot.

 

well there ya go and with having RP u can do no wrong

 

I thought you didn't have to use friction modifier with Royal Purple since it had it included? I'm pretty sure the bottle says it.

I'm running Royal Purple in my 8.8 and it has been running nice and smooth.

 

You are correct, the bottle and RP say you do not need it. Some choose to add the ford stuff also. When I changed over to Royal Purple I used the ford whale oil also. 75w140 in my diff also.

 

75W140 synthetic will be fine. At the last Ford parts & service meeting I attended, the engineers at Oakville told us to use the Motorcraft gear lube of that grade & type in any of the vehicles produced in the last 10 years, in place of the 80W90 mineral -based.


cheers
Ed N.

 

I just did a rear end in a Mach 1 and the friction modifier called for was purple and not the green stuff that I used in my buddies 2000 Gt. The parts guy told my that the friction modifer was was for synthetic gear oil. Question now is, is the green friction modifer ok with synthetics? Any answers for this
Ed.

 

The regular Ford friction modifier (old number C8AZ 19B546 A, now Motorcraft CXL-3 in Canada) is fine with 75W140 synthetic. For a few years in the early 2000s, Ford was using 75W90 synthetic in some vehicles, with it's own specific friction modifier, CXL-7. But now the service bulletins are instructing us to use 75W140 with the regular modifier when refilling any of those vehicles (mostly truck applications).


cheers
Ed N.