limited slip friction modifier

2nd Mustang

Founding Member
Feb 24, 2002
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46
Southern California
I have a nine inch rear end with a limited slip 3.25. I don't drive this car every week, but a few months ago, I noticed a slight humming noise from the rear end after the car warms up. The rear end housing looked wet so checked the lower two housing bolts and they were loose. I tightened them up and added a little gear lube but the humming still persists after a few minutes of driving. It's not as loud as before, but still there.

I'm just fishing for possible answers so could it be old gear lube or lack of limited slip friction modifier? I've owned this car for about 7 years so I don't know how old the gear lube is. Thanks.
 
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The friction modifier just ensures that the clutches in the LSD work properly and don't chatter. It doesn't affect lubrication of anything else and would not have anything to do with the humming.

At this point you may want to pull the chunk and have a look at the gears and bearings.
 
65ShelbyClone is right on, the friction modifier is simply for the correct operation of the LSD.

The humming noise is probably a worn out ring and/or pinion gear. If the oil level was low for a while, it may be time to check for bearings.