sweet99

Shop is starting my gear change tonight and I am not sure what gear oil to go with. I bought 3 qts. of MOBIL 1 75W-90 then I heard that a 85W-140 was recommended. Then the whole synthetic or conventional thing has me confused. I did pick up 2 bottles of posi additive if I go with a conventional gear oil. So what's the deal guys who have changed gears. What did you use and the results? Thanks, mark

BraMas

If you go with Royal Purple you do not need the friction modifer. If you want run what you bought to break the gears in and than change to RP. You shouldn't need two bottles of the fiction modifer I believe it is only 7 oz that is used out of the bottle

01yellowgt

royal purple gear max. cant remember off hand if its the 75/90 or the 85/140. check the manual for weight think its the 85/140, but I couldnt tell you whats in mine.

sweet99

The haynes manual says 80W90 and I got 75W-90 but I have read that a 140 was to be used as Ford probably changed the requirement. I was on the phone with Brenspeed and they said they use the friction modifyer with the synthetics also. I have 8oz. total of that. Now I just need to know if the 75W-90 will be OK or If I should get some of the 80W-140? Thanks, mark

Soaring

I put 75W90 Purple with the friction modifier in mine after a lot of research, and she has been running just fine for several thousand miles now.

Deannostang

75w-90 Royal Purple. No friction modifier needed and works to perfection in your differential. Cuts down drag on gears too. Use Royal Purple fluids in your engine, tranny and rearend and watch your mileage increase AND dynoed power curve.

royalpurple.com/techa/whyrpa.html

sweet99

Thanks. I feel better now. I was not sure if I should have gone out and gotten the heavier oil. Doing a search now to see what has been done in the past but needed some answers quick and I appreciate the quick responses. mark

ShadowDrake

Factory weight is 75w140. Royal purple does not sell this weight. I got 75w90 from Royal Purple, been in a couple thousand miles now without a single problem.

Soaring

It's only about 8 or 9 oz. of friction modifier. It certainly won't hurt, and as far as I can tell it helps with the heat. A small investment.

racemyski

Royal Purple does sell a 75-140 weight oil in their Gear Max line.
Do we have an authority that can say once and for all whether the friction modifier is necessary when using RP gear oil? Btw, this is for my 02 GT vert w/ a T3650.... manual calls for 75-140.

Any ideas??