When "topping off" a limited slip axle (like adding less than 12 ounces or so of fluid) would I have to add the friction modifier additive as well? I can see having to do it, like when doing a drain and refill.

The axle code in My 1994 F150 according to the door sticker is H9. Looking at the rear cover, i see no tag saying use limited slip additive, the tag on it says the following:

S847F

3L55 88 3K25

 

Add it in proportion to the amount of regular oil you added.

To be fair, it's pretty likely your limited slip is worn out anyways, so it wouldn't matter.

 

The 3L55 means it is a limited slip 3.55. They only take 4 ounces of the friction modifier during refill, so it's not a lot. I'd just top it off with a gear oil for limited slips or even the regular stuff, it probably doesn't matter.

If you're having to add fluid, check for leaks.

 

Thanks for the info, Mine is not leaking and level is full.Will use this for future reference