Differential fluid change - Additive?
 

1990 f250 e4od, Sterling 10.25, Dana 50.

Changed the gear oil in both differentials, Bought the expensive stuff -GL-5 Plus for limited slip differentials. Do I still have to add the friction modifier?

Yes, add the modifier. I'm running the high dollar synthetic fluid in both of my trucks. It's supposed to have the modifier in it already, but they chatter when I turn.

Thanks, I just wanted some reassurance before I dropped another $24 for the additive

wow it costs 24 bucks for that little 4 oz tube . I get it here for 2 bucks.

It's 8 bucks a tube here and the manual calls for 1 in the front and 2 in the rear! (so to speak):-X15

When changing the rear differential lube, how should one go about cleaning out the housing and gears before re-lubing the differential?

1989 F150 4X2 355 non LS

If you just drain all the old fluid and put new fluid in you should be fine but if you want to be very thorough...Drain all the old fluid. Put about 1/2 to 1 qt of new fluid in and roll the truck up and down the driveway once. - don't drive it, just spin the wheels a little to get the new fluid to "rinse" the inside of the housing and gears. drain again and refill. don't forget to add the really expensive additive if necessary.:-missingt

Where'd you get it? It's fairly cheap from Ford (definately under $10 a bottle) and it's guaranteed to be the right stuff. I don't know about some of that stuff in tubes at the parts stores.

Was that 1 bottle or 2 in the rear??? Lmao... Thanks.... :)

The 10.25" rear end calls for 8 oz. of friction modifier; the 8.8" rear end takes 4. I'm not sure how much is in the Ford bottles, I always add one to my half ton.

The Chilton says that my non LS only needs sae 80 or 90 without the modifier. Should I think differently? No sense spending the money if I dont need to. (Right busted??...lol)

I'm sure glad you guys have a sense of humor....:-X07

don't worry about it then. you only need it on certain models. But you probably want to buy the gear oil for LS diffs - GL-5 rated.

You only need the additve if you have a L/S. Go check the door tag and find the axle code and report back. A letter then a number will mean a L/S

If it gets a little dirty while you are working on it witch they do when I am laying in the dirt and the wind is blowing 20 MPH. I use a small pump up garden sprayer with solvent in it and give it a good flush just before you put the cover on

A can of brake clean works good too. Just make sure you get it all out. The 8.8" has a little cavity at the bottom that will collect it. I don't know for sure about the 10.25".