Would an incorrect GEM stop the Control Trac from engadging the vac hubs? | Ford Explorer Forums - Serious Explorations

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Would an incorrect GEM stop the Control Trac from engadging the vac hubs?

Hartman

Explorer Addict
Joined
October 16, 2001
Messages
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City, State
Indianapolis, IN
Year, Model & Trim Level
1996 5.0
Basically I'm trying to get my 4WD system to work. The transfer case engages in LOW, but the vacuum disconnect doesn't seem to be engaging the front wheels.

A while ago, I tried to track down a problem with the interior lights and swapped GEMs. I got two new GEMs in total, one of which being from a 97+ truck (non vac operated). It is possible that I have that GEM in my truck right now. My question is, would that stop the vac disconnect from operating? The lights come on in the dash and the shift motor engages, but but the wheels are receiving no power.

Also, I pulled the fuse for the ABS system because the front sensors are bad. Will this effect operation of the AUTO setting?
 



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the vacuum disconnect on the front axle passenger side correct? no vacuum hubs on these trucks thank god
 






yep.
 






yes if the GEM is not wired properly the solenoids on the vacuum disco wont work.
I am guessing you recently replaced the GEM?
 






there is a thread here somewhere that details how to tap into the wires to turn the vac hubs on and off at your own will...I think Jdraper wrote it for people who swapped in 1354man cases, but it might work in your case....

Edit: here is the thread
http://www.explorerforum.com/forums/showthread.php?t=88718
 






Awesome I will give that a try. Is this the same mod that will allow 95-96s to have 4HI? So if I have it in 4AUTO and flip the switch, that will technically be 4HI right?
 






It's a different mod...

The GEM grounds the vacuum solenoids that control the Center Axle Disconnect. If you have the GEM from a 97 in there (which would be surprising as I thought that the pinouts were slightly different), then yes, that could explain the problem... But I would also think that if you had a 97 GEM in there, you'd also have the ability to run 4auto, 4high, and 4low instead of 2wd, 4auto and 4low. The 97 is not programmed for the CAD, or for 2wd AFAIK.

Now, as for troubleshooting your problem, pull the connectors off the vacuum solenoids and check to see if the GEM grounds them properly. With the key on and the engine idling in park, you should have power on both solenoids, and one should have continuity to ground, the other shouldn't. When you switch to 4auto, the engage solenoid should ground, and the disengage solenoid ground path should be open.

Now, if it was mine, the first place I'd start would be at the t-case itself... make sure the case locks the driveshafts together. Then, move on to the CAD, checking for vacuum on the apropriate solenoid at the correct time, then chase the hoses if necessary, and play with the CAD itself if it gets that far.

-Joe
 






Great timing to have no 4x4 :p: That really sucks. But I'd follow what was mentioned in the post above me!
 






Great timing to have no 4x4 :p: That really sucks. But I'd follow what was mentioned in the post above me!

No kidding. It's bad enough having 2WD, plus I have absolutely no weight over the rear end, so I get 0 traction. I might as well be driving a car. Embarassing.
 












Well today I had some time to troubleshoot. First thing I did was check the two vac lines going to the axle. I had my dad see if there was any vacuum in the lines while I switched on the 4WD. He said he felt vacuum in the white colored line but not the black one.

Since I was getting at least partial vacuum, I put it back together and took it for a spin. Wow, somehow the system was working both in auto and low. So I parked it, filled up the front diff (low on fluid), and figured the problem was fixed. However, when I went to leave a couple hours later, I put it in 4LOW and the front wheels were not turning. I tried shifting it in an out of 4WD numerous times with no avail.

I guess the damn thing just works when it wants to. I'm guessing I have a vacuum issue somewhere, perhaps the vacuum modulator. Any thoughts?
 






mines been doing sorta the same thing...dosent want to engage the hubs when the motor is cold, but has no problem once its warmed up, but I also have a vacuum leak at the upper intake causing it to run lean (need to get that fixed) so I have just been attribuiting my 4x4 problems to that.... maybe try the propane trick to see if you have a vacuum leak anywhere?
 






Yeah I'm almost sure I have a vacuum leak somewhere, I just can't find it. Until then, I'll probably just engage the 4WD a couple times each day to try to see if it frees itself up, if the vacuum disconnect is indeed sticking.
 






Get a can of starter fluid. Your idle will rev up when you spray it over the leak.

If you have a vac leak and a crappy idle, you may have terrible vacuum which might not give you enough for the center axle disco to kick in.

Go to autozone, for next to nothing they have a pressure gauge you can hook up to a vacuum line and see what your getting. You can test the solenoids, see if they go on and off. I'd check the vacuum at the axle, maybe you have some but not enough. Compare it with vacuum at intake manifold (should be the same unless there is an ubstruction in the line).
 






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