Thinking about using RP in my rear diff and looking for the experience of others. It has the friction modifier in it already, and that is what concerns me - I will have no option to use more or less.

My LS actually works fairly well, and I would like to keep it that way.

Your experience?

 

Im using RP in both of my diffs with no problems. I also use their tranny fluid in my T-case.
~Gage~

 

I'm not sure I understand the point. With regular changes every 100,000 miles, your axles will probably outlast everything else in the truck just by using the manufacturer specified fluid. Why buy expensive synthetics?

 

Yea why? Also; Mobil one makes it in LS and non-LS

 

Synthetic is required by Ford, so it's either get it at the dealer, or get a good alternative. I think the RP will be less expensive at Pep Boys than the Ford product at the dealer.

In general I agree with you, and I'm not a fan of Royal Purple or any other over priced alternative lubricant. But in this case, the Ford product seems to be less convenient.

I don't believe in the 100k service interval. I'm doing it at 60k. Towing.

 

I guess my question would be the same - does Mobil get the friction modifier right straight out of the bottle?

 

Makes sense to me, Bill. Have you looked at the parts store for other types of synthetic? If I remember right, it's fairly common to see for a reasonable price.

 

There is mobile and moble ls.

 

I've had RP 75W140 in my rear diff for 60k+ with no problems. I liked the fact that I didn't have to 'guess' at the mixture; just fill to the proper level & go.

 

But it is a case by case prognosis. If the clutches don't chatter on a sharp turn, leave it alone.

 

Funny thing. My rear diff made a slight whine at highway cruise from brand-new. Never changed, never got any better, but was so slight it wasn't worth doing anything about.

Had to clean up the rear cover, changed out diff fluid to royal purple.

Noise got a LITTLE bit quieter, but didn't go away.

Had a leak, had to fix it, and tried Mobil 1 this time.

NO NOISE.

As for the LS additive, are you sure it has the additive, or it's billed as "not requiring it"?

 

I recently did mine with AMSOIL and it has FM in it and the LS worked perfect after the change. Price was cheaper then valvoline synthetic....I have heard the RP is good stuff too.

 

Royal Purple Gear Oil

 

I been using Amsoil in all my trucks. Every truck required a little additional modifier. I would get less than 100 miles and the chatter would begin so I would add 1 oz at a time until I didn't get any chatter. Each truck/time required a different amount.

I think the amount depended on the condition of the clutches. Older or more worn clutches probably take less.

 

No matter how you cut it, 75w140 is expensive!!!! I have 60K on the clock and have a nice finned aluminum cover sitting in the garage, but damn near $70 for 4 qts of liquid gold LOL