Differential fluid questions

[AutoDoc]

I posted this on the LWB forum, but thought someone over here may be able to help as well...

Hello all. I decided to change the gear oil in my differentials today (2005 Rubicon unlimited) for the first time and I'm confused about what to put back in there. I put 75W145 full syn in both "rears", but when I was reassembling everything I noticed the metal tags that were bolted to the rears. The front says 44 oz. 80W90, and the rear says 60 oz. 75W145 + 4 oz. FM. I guess that means I've got to suck out 4 oz. from the rear diff and find some limited slip mojo and dump 4 oz. of that in there. Is that stuff commonly available, or do I have to get raked over the coals by the stealer for it? And what bad things will happen if I don't put it in there?

[StrongWind]

"FM" is friction modifier for the limited slip....but you say you have a Rubicon? Doesn't that have the electric lockers? I didn't think the electric lockers would require LS FM.....I thought the friction modifier was for the clutch style limited slips?.......Is it required for the electric lockers also? New one for me...I've got an old YJ with a Truetrac.....

For clutch style limited slips, the FM works with the clutch plates to make it "limited slip"....Without the FM you will probably ruin the clutch plates in the limited slip and not have a very effective LS...

You can get the LS "mojo" at a good auto parts store - just find a parts guy and tell him what you are looking for. After you add it, go find a parking lot and do several figure "8's" (slowly) to work the fluid into the clutch plates (if you have them...)

[AutoDoc]

That's what had me confused. I have pneumatic lockers and didn't think I had limited slip, but like I said, the metal tag bolted to the rear diff says to put in 4 oz of FM. I guess I'm just gonna put the stuff in. Better safe than sorry.

[Jerry Bransford]

The Rubicon's rear axle also has a limited slip differential for when the locker isn't locked up.

[brkitnowfixit]

check your bottles of fluid most come with a friction modifier already in them

[StrongWind]

Originally posted by Jerry Bransford:
The Rubicon's rear axle also has a limited slip differential for when the locker isn't locked up. I understand that - but isn't it a gear driven limited slip (like the Truetrac) when it is not engaged - no clutch plates? I didn't think it would require FM?

Call me curious....

[xr8dxj]

Originally posted by AutoDoc:
I posted this on the LWB forum, but thought someone over here may be able to help as well...

Blasphemy! Originally posted by xr8dxj:
Welcome to the board with your LWB Rubi. Its a great rig. The diff fluid shouldn't be that hard to track down. My Dad uses Synthetic 75W145 Gear Lube by AMSOIL in his F350 rear limited slip.

[AutoDoc]

OK everybody can relax, it's over LOL. I found some Magic Mojo at the local parts store (CRC Trans-X Posi-Trac) for about $5. I sucked out some gear oil and shot about 4 oz. of the mojo back in. Now I can sleep at night except for the guilt over using my wife's turkey baster to suck out the gear oil which brings me to another question... Do you think she'll be able to taste it? I cleaned it out pretty good with kerosene.

[edudley]

Actually brkitnowfixit is right. Its been a while since I saw any gear oil without a FM in it.