Rocket254

I'm finally ready to install FRPP 4.10s into my '08 GT/CS that I've had sitting in my garage since December. I picked up the bundle kit from AM that includes:

Ford Racing 4.10 Gears - 8.8"
Motive 8.8" Rear End Installation and Bearing Kit
1 bottle of Ford Racing Friction Modifier
2 quarts of Royal Purple Max Gear 75w90 Gear Oil

1) I've heard conflicting reports on whether I need 2 or 3 quarts of Gear Oil.

2) Friction Modifier. Need it? Don't need it?

What else should I know before dropping the car off to have the work done? I'm just looking for as much extra info as I can so I don't get fleeced by the installer.

rls82959

I had mine done a couple years ago.
Went with Amsoil 75W-140 I believe and the ford friction modifier.
Used 2 Qts and a few drops of the 3rd bottle.
Installer can use the gasket that came with the kit or a tube of gasket maker sealer.
All you need now is an experienced/slow (not in a hurry) installer.
I remember my installer saying backlash is critical and 8.8's are not forgiving.
He got the backlash dead on and 2 years later its very quiet.
Good luck

tx_zstang

With stock rear end cover, 2 quarts plus the friction modifier is enough; and yes, you do need the friction modifier, even with royal purple. (I'd go with a higher viscosity instead of 90w.)

Rocket254

Thanks for the replies. Tx, I'm guessing something like 75W-140 (as mentioned above) would work well?

Would you have any preference as to brand? I'm running RP transmission fluid at the moment and it is pretty much a "meh" for me. Still gets hot in the summer.

jz

I have never heard of anyone putting in the friction modifier when using Royal Purple. I changed my gears years ago using Royal Purple, and did not use the friction modifier. If memory serves, I believe it even says on either AM or Royal Purple's website that you "do not need friction modifier".

tx_zstang

*** ME ***
Had to add the fm to royal purple, when the rear end started groaning on low-speed turns. I knew it needed friction modifier, so I added it then and of course it stopped. These were with a GT500 rear end, though, and other rear ends might not exhibit the low-speed grabbing symptoms.

Now in every rear end that I put RP in, I also put in friction modifier while I'm at it. But you could take the chance and wait and see if you do end up needing it, then add it later. But if you have it, just put it in and save the time and hassle of having to do it later.

Rocket254

Is there any negative effect of adding FM to gear oil that claims to not need it? Seems like one of those "Rather have it and not need it then..." cases.

About to order the oil this afternoon. Amsoil or RP 75W-140?

tx_zstang

Both are good choices.
If you use a synthetic, then go head and put the fm in if you have it.
I wouldn't add it to a high-quality conventional oil unless it needs it or recommends it.

I use only RP, which I or others get from latemodelrestoration.com as part of an install kit.

Rocket254

Thanks. I'm ordering the 140 RP now.

I'm planning on picking up the TLOK Rebuild Clutch Packs as well. Worth it @ 56K miles?