'97 4WD engages during turns on dry surface

[steve300]

Apologies in advance - I am a totaly newbie to this site, to Explorers and to automatic 4WDs in general.

I have a used '97 with the Auto/4HI/4LO switch. Several months ago it started shifting itself into 4WD during sharp turns to either side. During one such self-engagement, the main shaft inside the tranny shattered while turning onto a busy highway. I had the transfer case, clutch and tranny replaced. Within a few months, the same problem is recurring. No lights flash, no real noises, just severe jerking back and forth as you turn and it goes into 4WD. Problem is intermittent but ongoing.

A Ford diagnostic reports no computer/sensor problems so they want to replace the same drive chain again. Six dealerships and two independents have either different answers or don't know. Fluids are clean and full in the cases.

The X also has a 'check engine' light that turns on when you fill the gas tank and then drive it enough to warm the engine (Ford can't diagnose) and both reverse lights have stopped working. I assume these problems are unrelated however they are occuring at the same time.

Thank you in advance for any help.
Steve300

 

[TPLYNCH]

4x4 engagement in Auto is controlled by the GEM via input from the speed sensors on the t/f case. Normally if the sensors are bad, you'll get flashing 4x4 lights (6 flashes, repeated every minute or so). There were problems with the GEM, and I believe a recall was done on the '97's to reflash them to alleviate harsh engagement. I'd start with having the GEM reflashed and see if that helps. The GEM controls everything electronic in the Ex, so any other strange electrical gremlins you might have might lead to the GEM being defective....

 

[glfredrick]

I've got a 97 that does exactly the same thing and I am on my 3rd GEM.

It seems that when Ford bought that design t-case from Borg Warner they didn't want to pay extra for the NICE computer (GEM) that BW had which incorporated a speed sensor in each wheel to calculate turning wheel speed, so when we turn, the transfer case senses a difference between axle speeds and kicks in.

Some have done the "brown wire" modification to turn off the auto feature. You can find lots of links to that if you search.

What I do that helps is to drain and refill the t-case on a REGULAR basis (about double the frequency of motor oil) with fresh oil - that seems to help. Also keep the air PSI in the tires set accuraely all the way around. That also affects it. The third thing that actually helps is to run the truck in all ranges on wet slippery surfaces once in a while to keep everything lubed up.

Other than that, you sort of just get to live with it. It doesn't really hurt anything, it is just agravating at times, and some of us live in areas where the auto feature is the primary reason we bought the truck. In my case, my wife drives the Ex on the freeway everyday to work - and the roads are subject to black ice at a moment's notice. It sure is nice for that...