08JD

i really need some help and it now. I have a big issue with the 4X4 system. When im in 4H i notice if i make a turn sometimes a wheel will lock up, and skid as if my brakes we're applied. 4L doesn't even want to engage, it will grind and also, if I'm in 2H just driving and make a turn sometimes i will have a vibration from my rear end in the axle. Could it be the pinion gears? or bad transfer case? Its a 1999 F-150 4x4 5.4L Automatic/Manual selector for the 4X4 and 170,000 miles. If anyone could help me it would be great! Of course there are going to be problems, but im looking to not spend that much money. Get back to me f150forums. I appreciate anyone who gives their input greatly! it means alot.

-derenzo.

p.s. could i have bad lsd's in both axles and this explains all of this?

Dirtbuster1

4 wheel drive is always going to try and lock up to some degree on highway roads. If the rear end is popping in 2H when making some type of turn, it probably just needs some limited slip additive. If the front end is trying to lock up like brakes, it could be a similar problem. Do you ever put your truck in 4 wheel drive much? Try putting in some additive in the fill holes on the differential, then take it and drive it in some sand. Do some fiqure 8's until it start to quite down.

Hope this helps!

08JD

worth a try! what does the additive usually do? im not sure if the previous owner really used the 4x4 system. and location of fill holes?

Dirtbuster1

The additive allows the clutches to slip while turning. You usually have to add some every 20k miles or so.

08JD

lol, wow, i doubt its been done in a while :/. thank you very much, im going to give it a try asap. I bought the truck for 4 grand and its been amazing ever since. Even though my tape player stopped working and i had to hit my dash to get it going again. It works now, but i got a inch crack in my dash fml.

dbok

the additive you should try is called "friction modifier" from your local ford dealer. i am not sure if a local part store woul dhave it or not.

take off the differeantial cover plug and fill there, then top of with gear oil 80w90. I had a similar and it was because my axle seals were leaking at the wheels and i never noticed it. topped it off the modifier and 80w90 and all is good. i check it about once ro twice a year now.

08JD

worth a try! i will do it asap. do i use the whole bottle per axle? wont hurt anything?

Dirtbuster1

If you have to add differential fluid, it is 75w-140w. If you add the Mobil1 product, it will have the additive built into the fluid. It take 6 pints to replace all of the fluid. You need to remove the cover to get all of the old fluid out. When removing the cover you can also see if there is a problem that might be lurking around the corner. I just did mine 2 weeks ago.

6 pints = 60.00.

08JD

i'm guessing you then replace the gasket on the cover? also, you recommend me doing both axles? also where is the "fill hole" located?

08JD

i appreciate both of you guy's help. But my next question is, which is the best way to do it. get the additive and just pour that in and top it off with 80w-90, or just take off the whole plate, drain it, change the gasket, and fill with the mobile? what do you guy's think, also does the gasket really need to be changed? is it even a gasket that ford uses down there? as you can see im not experienced in axles, just everything else lol.