Originally Posted by 847alexc

Whoa!! don't put 80-90 in your 97 f-150!

While your right, most limited slips will require friction modifier for the limited slip, that is exactly why the ford OEM is the wide viscosity 75-110. The variable viscosity eliminates the need for friction additive. They did this because so many cars were having L/S clutch problems even with the additive. Some techs I know would use 2 tubes of the stuff just to be sure. The older 8.8 L/S used this stuff and its ok, but the 75-110 is fool proof. It just so happens that its synthetic because its the only way to get those viscosity properties. Without either 75-110 or the right amount of additive you will burn up your L/S, though now even open diffs are meant to run the 75-110 on newer fords.

But as far as the axle bearings, the biggest problem is that the seals are prone to leaking. When enough fluid leaks out the bearings dont get the proper lubrication causing failure. Eventually the bad bearing even wears into the axle it self making the repair much more expensive.

Check you seals for leaks whenever the wheel is off.