4X4 trouble on my '91

[ItsNotAJeep]

My 91 EX won't engage 4WD. It wouldn't go into 4L for a long time but I didn't really need it so didn't address it. Now the snow is falling and I can't get it into 4H.
Nothing happens at all when I hit the button. I searched around for a bit but all the topics seemed to be about rebuilding the shift motor.
I read through the troubleshooting sticky and got as far as checking the module. Performed the test and the relays click and the LED flashes properly on the self test.
I pulled the switch out of the dash and checked continuity between the pins when I push the buttons so I don't think that is it.
Any thoughts?
If this has been covered in another thread I would be grateful for the link.
Thanks in advance.

 

[coco944x4s]

Most often this concern is related to the shift motor, that is why most of the stuff you find on here involves the shift motor. Tap on the shift motor with a hammer and then try hitting the buttons again. Used this a few times to figure out the motor was bad.

 

[Four0Sport]

leave the shift motor electrical plug in connected but remove it from the tcase and see if the motor is working correctly. lots of good info in that shift motor rebuild thread..

 

[awood]

Shift motor.

Very common for your issue. I would read all the steps completely through a few times first before actually attempting the fix. Go slow and take your time. I'm positive you'll get a fix. If not, you've prevented a problem down the road.

 

[ItsNotAJeep]

So, tell me this. Is there a reason not to just go pull a shift motor out of the salvage yard instead of rebuilding?
Vehicle as a whole has 230K+ miles, put a salvage motor in it a couple years ago.
Salvage yard has been good to me.

 

[awood]

Yes. It is very likely that the salvage shift motor has the same problem. There were two main issues with the shift motor as I recall. First, the switch plate gets corroded - especially when it hasn't been used for a long time. Using 4WD more often will actually help prevent the need for a rebuild in this area. There is also a rubber bumper on a stop pin (movement limiter). Over time, that too will get brittle and break away, leaving little pieces inside. It's been a few years since I did mine, but that's what I remember.

You can remove the shift motor without putting your Ex out of service. If you need 4WD while the motor is off, you can crawl underneath and rotate the shaft (with pliers or something) to engage it if you need.

The link below is a good reference. Picture 6 and 8 show the switch plate and stop pin. These have been cleaned up. Mine were much more dirty.

http://www.explorerforum.com/forums/showthread.php?p=1102904

 

[DeRocha]

I just fixed another shift motor for a friend the other day. The plastic stop was the culprit (as it is 95% of the time). Just do the steps to replace the bushing and ignore the steps where you need to clean the electrical brushes and you'll be up in running in short order..

I you have any problems or questions hit me up...

 

[ItsNotAJeep]

Finally have some time to work on this tomorrow.
If you wouldn't mind, what is the sequence of operation here? When the module is plugged in and I push the button nothing happens, no relays clicking, etc. It seems like there is a switch open or something.
Is this in the position sensor? It seems like that stop only comes into play when the motor moves. That's why I didn't think that was the problem originally. Willing to take you fine people's word for it but just seeking to understand a little better.
My lazy has been in full force this week, haven't even climbed under it since I posted this.

 

[awood]

I'm not sure, but I think during the last operation where it actually worked (when the motor turned the gearbox and switch plate) with the bumper missing it could over-rotate, allowing the contacts to travel off the switch plate contacts. For the next operation, since the contacts were off the plate, there was no electrical connection.

It's just a guess since it's been so long...

 

[DeRocha]

Yup...when the stop falls apart it can cause 1 of 2 things to happen.

• It can allow the geared position sensor to move out of range making the 4x4 computer blind (pressing 4x4 will do nothing).
• It can cause the worm gear to over torque the geared sensor jamming it against the Metal post. Pressing 4x4 will engage the shift motor (for a few seconds), but the motor will not be strong enough to move it.

I'm not sure, but I think during the last operation where it actually worked (when the motor turned the gearbox and switch plate) with the bumper missing it could over-rotate, allowing the contacts to travel off the switch plate contacts. For the next operation, since the contacts were off the plate, there was no electrical connection.

It's just a guess since it's been so long...

 

[Mettler]

Just rebuild it! It is so damn easy, when your done you"ll look back on your procrastination and go, "Dumb ass, that was so easy! I should've done this sooner!" It really is easy. Really easy. So easy a caveman can do it.