Mulestang

I've spent some time searching this subject, and can't seem to find a solid answer. Do I still need to use 4oz friction modifier in my rear diffy (code B6) if I'm using RP 75W 140 MaxGear? The label says it has the additive already, but there seems to be no consensus. I'm able to get the RP MaxGear for $10 a bottle (through a friend), but if there is any chance of screwing something up, whether it be the RP itself or the additive issue, I'm ok spending the extra $ on the Motorcraft lube. Any personal experience or advice is appreciated.

HulluCorn

I would say yes, add the friction modifier.

Martian

Just go with Motorcraft and you'll know for sure you're good.

Toshbar

No matter what you buy, you need to add the FM. You can try it out without it, but likely the rear end will chatter when you make accelerating tight turns from stationary, such as pulling out from a stop sign.

Hootsworth

Yes, add it.

I actually used the Royal Purple MaxGear. Even though it says "Includes Friction Modifer" it doesn't appear to be quite enough. When I did my Rear Diff. change (changed due to diff. shudder/chatter) I used the RP fluid. It helped, but there was still a slight chatter. It was only once I added a 4oz bottle of Motorcraft FM that it went away completely.

Toshbar

I had the same experience with Valvoline synthetic.

HeathMc

I used royal purple and didn't have to add any. I'd do the service and run out and do some figure 8's in a empty parking lot. If it was good I'd leave it alone. If I got chatter then I'd add some. Too much can also be bad. Just my opinion.

60DRB

I also used the RP, and I did add the Ford friction modifier. 70k miles since and no issues.


Don't get the FM on your hands...that stuff REEKS!