I have a 99 4.6 96k miles, auto, 4x4 w/ SOTF. I'm having a problem with 4WD. The problem is that it does not feel like it is engaging the front axle when I switch to HIGH. I don't feel the thunk I used to when I shifted into HIGH. The dash indicator light says "High". Any help would be appreciated.

Also the 4x4 switch light bulb is out. Does anyone know if it is a bulb or if the switch needs to be relaced?
thanks
-jeff

 

Got the EXACT problem on my 97 expedition. If the mechanics work the same, Here is my list of trouble shoots you can follow. First of all see if it operates on vacuum.
Look underneath on your differential. There is a black shroud that covers a bellows piston actuator. It should move while switching between 2x4 and 4x4 (engine running).
If not, Trace the two vacuum lines that connect to it. (At first I thought they were electrical). You can trace these to a triangular coupling on passenger wheel well inside the engine compartment. Disconnect here and see if vacuum toggles between the two lines when switching between 4x4 and 2x4 (I measured 22"hg).
If toggling OK check to see if vacuum is holding down stream at the bellows and not leaking by. A vacuum pump and gauge is necessary for this.
If seals are OK and the bellow is not moving the fork, you’re in the same boat I'm in. The fork has seized leading into the differential.
I tried moving the piston by hand and the damn thing is acting like it's wedged. I've been working on this for the last two weeks and I’ve now washed my hands. I dropped it of at the shop a few hrs ago. The guy agreed with trouble shoot so far and suspects sized fork theory as apparently he has fixed these a few times already. I will let you know out come tomorrow when it's out of the shop.

 

I had sort of the same problem a while back, only sometimes it woulden't come out of 4 wheel drive and sometimes it woulden't go in. turned out to be ice in the vaccume line.
wayne

 

Just got the word. The fork was stuck. He dropped the assembly lubricated and put it back together. All fixed for
$65. He recommended engaging 4x4 once a month and spraying a little lubricant up there every now and then.

 

Hopefully that is all it will be. Thanks for all the info. Any help on the light on the switch?

 

If it's just the light on the **** I would see if you could access the wiring from behind and ohm out the bulb. there should be a resistance value somewhere I guess in the 100 ohm range. If it's its open replace the bulb. If it's ok then I don't know where to look. Maybe trace the wires and look for a break or something loose.

 

It turned out to be part of the vacuum system. There are 2 identical parts mounted on the pass. side firewall near the battery. One of those went bad. I don't know what it's called. Easy change, dealer had to order ($40).

The switch has a special bulb with a weird base on it. You have to change the whole switch. You can't by the bulb. It kills me to have to buy the switch ($42) but I'll probablly do it

Thanks again

 

m1j, glad you got your 4X4 working. I'm having a similar problem with mine (98 4.6) just wondering if you could post the part # of the vacuum component you replaced.

Thanks Mark