I am having a problem with my 1998 F150 4x4. The 4WD is not engaging. It is a manual shift. I have checked the transfer case by turning the drive shaft in 2WD it is free. When I shift into 4WD it is does not spin freely. So I believe that is OK. I have checked the vaccum diaphram. It will move the piston when I attach a hose and pull vacuum on the inboard hose barb. So I believe the diaphram it self is OK. I am not sure if the hoses and selenoids are OK. They look fine. However there is a constant vacuum on the inboard hose line (red/pink color) wether I am in 4WD or not. Is this OK? How can I check the selenoids. If all this is OK, the next thing I believ it could be is the shift fork in the differential. Is that a difficult job? Do you need to pull the whole axle out to replace it?

Thanks for your help.

 

It sounds like the 2wd solenoid is stuck.... when in 4wd, do you have vacuum on BOTH hoses? If so, that's quite common.... the 2wd solenoid fails to disengage, so you end up with vacuum on both sides of the diaphragm, and nothing moves.

Try disconnecting and capping the pink line at the solenoid, and engage the 4wd. See if that fixes it. If so, replace that solenoid.

-Joe

 

I just fixed it last night. Based on other posts I have seen I checked the switch on the transfer case. It did not seem to be working. I bought the replacement from Ford ($32) and replaced it. I was delighted when I pulled the lever and it actually engaged the 4wd. This was a nice easy fix.

 

Well, I guess I was half-right.... the solenoid wasn't engaging the front end... but it was because the GEM wasn't getting the feedback signal from the transfer case to say it was engaging 4wd and then tell the front end to engage.

Glad you got it fixed.

-Joe