Friction Modifier in non-limited-slip differential?

[TheG]

So, here's the deal:

Have a 2002 explorer with a code 45 (open 3.55) rear differential. 135,000+ miles.

It has the rear diff whine that the Internet tells me is extremely common, and that many have failed to correct it (even after expensive repairs).

The noise didn't bother me much until I recently purchased quiet tires. Now it's noticeable, mostly when holding constant speed.

I change the diff fluid with (75-140) synthetic oil every summer, which doesn't seem to help a whole lot. I've even used synth fluid that "already has LS modifier" (though I am skeptical of their claims). I'm considering buying a bottle of friction modifier in an attempt to quiet it down.

So, 3 questions, sorry if they are ignorant:
1) Is it ok to put friction modifier in a non-LS diff?
2) If I use the oil in my garage that claims to already have it, can adding more be dangerous?
3) Any other additives that might have some hope of quieting it down?

Thank you!

 

[kert0307]

The friction modifier is only there to get the right friction between the LS clutch plates. Adding more modifier isn't doing anything except putting more money into a "failing" rear diff. The only thing that I could see possibly helping with noise it to go to a "heavier/thicker" weight oil. But long term you'll probably want to get it fixed "right."

 

[TheG]

Thanks for your input! Is there a viscosity you'd recommend? (I'd imagine there's a such thing as "too thick")

 

[TheG]

I'm thinking about trying 80/140 oil to quiet it down in the short term. Does this sound reasonable? (sorry for the ignorant questions. This is an area I know not much about)

 

[imp]

I'm thinking about trying 80/140 oil to quiet it down in the short term. Does this sound reasonable? (sorry for the ignorant questions. This is an area I know not much about)

Be certain if you go to heavier lubricant, that it carries spewcification for Hypoid Gears. The designations run from GL-1, GL-2, GL-3, GL-4, depending upon the severity of useage. (GL stands for "Gear Lubricant").

140 or 180 weight gear lube will be extremely "stiff" in very cold weather; however, they ALL thin out considerably when they get hot during use. Heavier lube will decrease gear noise, IF the noise is due to damaged (scored) or misaligned gear teeth, which produces anything from a "hum" to a down-and-out shriek.

In vehicles driven very hard, real cold heavy lube adds considerable turning torque to the driveline: i.e. U-Joints. Good idea not to "push it" until the differential warms up a bit, couple miles, anyway. imp