SyNdicateZ

I'll be getting 4.10 gear installed this spring and was wondering which oil to get and is bet for my differential..? I have a 02 gt coupe with 91,000 miles... Do I go with the royal purple 75w90 or 75w140 ger oil? I'll also be adding in the Ford Racing friction modifier as well.. Thx for your experienced advice !

jpplaw

75w140

cliffyk

You do not need to (and shouldn't) add friction modifier if using RP Max Gear oil. like most synthetic oils it is sufficiently slippery to not need the f/m additive...

SyNdicateZ

Everyone else says to...even americanmuscle.com...?

cliffyk

If you follow the link to RPs website you will find they say no.

from that site:
"Max Gear is formulated with a friction modifier additive – no additional additives are necessary."

One would think they would be a more authoritative source for this information, more so that "Everyone" or "even American Muscle"...

SyNdicateZ

That's just a good sales pitch to say..."hey!, buy our product, u won't have to add annyytthhiinngg else...." and then u have gear whine after only using the RP and not going with the added friction modifier.

cliffyk

Now you are just being silly. Most synthetic gear oils are sufficiently slippery to not need additional friction modifier. Beyond that, f/m has nothing to do with gear whine, its purpose is to keep the Traction-loc clutch packs from binding up and creaking, cracking and jumping as you negotiate tight turns.

You may certainly add more if you like however all it will do is make the LSD less effective. In the old days we ran little to no friction modifier as a "poor mans" way to get the differential to lock up...

Luke13

I used the 75w140 in my 2003 v6, 3.73 gears, and a used t-lock. Didn't add any friction modifier, and 50,000 miles later everything is working fine.

Seabee1993

American muscle couldn't even tell me which adapters i need for my injectors. I did my own research and picked cliffyk's brain to figure the difference of EV1/EV6/jetronic/USCAR. Now my stuff is on order and on the way. Don't rely on these retailers to point you in the right direction.

uberstang1

You definatly don't need modifier with RP adding more will increase the chance of a 1 wheel peel