Hi everyone. Recently bought a 99 Expedition with 5.4 and 4wd, 125k miles. When purchased, I installed new plugs, 2 coils, changed all filters, coolant, pcv.

Decided to take vehicle on 800 mi journey, as was running great. Somewhere along the way the front drivers tire developed a leak and dropped to 16 psi, meanwhile the rear passenger tire went bald (all were @ 6/32's). Also was experiencing some occasional driveline shudder.

Once I arrived at my location, I noticed the low tire, fixed it and all seemed well. Needed to make a 300 mile round-trip, so bought a new tire to replace bald one. Everything was smooth for the first 150 miles, until I came to a stop, felt like I had a drag. 3 hours later, go to leave and drag was worse than ever. Drove approx. 65 miles, but began smelling a "hot grease" odor. Pulled into a service area, applied the brakes and the truck moaned to a stop.

Decided to call allstate roadside assistance for help and waited an hour for nothing, figured that was enough time for expy to cool off. Got into the expedition, met a little resistance backing up, but then it was fine, drove the remaining 85 miles with no problems.

As a result of all of this I changed my diff fluids and transfer case fluids... transfer case looked like motor oil, though no shavings in it. Diffs were clean.

I'm a home mechanic, but am not familiar with 4wd or "a4wd", and figure someone must have gone through hell with this setup before.

Sorry for the preview, but the questions are :

a. Do I need 4 equal tread tires for this system? and could 1 tire having low pressure, or more tread cause the 4wd system to go crazy?

b. Or am I experiencing a malfunction with the GEM module I've been reading so much about?

c. Or is it something else?

I'm somewhat lost here, and really need advice, as I need to make the 800 mi drive home and another forum has ,so far, not been helpful.

Any help is appreciated.

 

quick answer. You dont need 4 equal tires just 2 equal per axle. Having different diameter tires on one axle can cause some SERIOUS problems. I belive in that expo each tire is monitored for speed so when on is moving at aconsiderably different speed than the other its contsantly trying to adjust basically thinking its slipping all the time.

at very least ALWAYS buy tires in PAIRS

 

I just did a Transfer Case fluid swap to Royal Purple Max ATF, the old ATF in the transfer case does indeed look like Motor Oil.

I run my A4WD 24/7 in my 2004 and have had no issues. (Currently 85k Miles) As previously posted it is important to have match set of tires. I was told when I had to "funny worn tires" it was best to replace all of them if I was running AwD with a match set.

Or course there is many changes from 99 to 2004'

If you already haven't checked:

U-Joints
Wheels for metal or Excessive Heat ( this would be wheel bearing)

Brake lines for bulging, or excessive wear.
Check your brake fluid

Since you smelled Hot Grease, try to check any part that uses Grease.

Also inspect your exhuast for grease splatter which could have been from U Joints, if the drive shaft over heating.

I hope some these suggestions help. I just checked and I have a 2007 copy of 1999 Expediton Service manual. I looked and the only thing I saw that referred to dragging involved the brakes.


I hope some of this helps.

 

Hey guys, thanks for the help.

So far I've got all new , matching tires ($$$$ ). And am going through the brakes as we speak. Replaced the rear rotors, pads and parking brake. Rear axle had drag from brakes and one rotor/pad set was scored pretty badly; the parking prake shoes had come unglued and were "floating" in the drum.

Front pads had equal wear, looked good and can't seem to remove rotors without destroying the vehicle, so I'll assume they're good.

Will update when I finish up and road test this thing.