Trouble with 4WD

[GMC Hauler]

I have been having problems with my 4WD. I have the newer motorized front axle engaging unit. I also have the floor lever style 4WD (no pushbuttons)

I took a look at the schematics, and there is a switch in the transfer case that provides electrical power to the front axle once the 4WD is engaged in the transfer case.

I checked power at the front axle with the transfer case in 4WD high. There was power available, and the engage signal was present.

My question to you is:

When the lever is in 4WD high or low, does that mean that the gears are engaged in the transfer case?

If so, that should mean that the transfer case switch should be engaged?

Has anyone had any problems with the replacement motor style front axle engaging units being intermittent or going out?

When the lever is in 4WD high or low, that means the front driveshaft should spin, correct?

Anything i am missing??

[More Power]

The lever physically engages the various gears in the txfer case. A 4x4 lamp on the txfer case console on the floor should illuminate once (only when) the front axle has engaged.

You could remove the front axle solenoid, plug it into the electrical harness, then activate the txfer case lever to see whether the plunger in the solenoid moves back and forth.

Jim

[Robyn]

The servo motor type units are better than the older Thermal actuator BUTTTTTTTTTTT even the servos can quit.

Like Jim mentiioned, plug the unit into the harness and see if it works when the shifter is engaged.


Robyn

[GMC Hauler]

It works, intermittently now. Once it is engaged, it stays engaged.

We noticed something. Sometimes it engages, but the light does not come on. You can tell by the feel while steering. Where is the switch at that tells us the front axle is engaged?

It also seems to have problems disengaging occasionally.

Haven't had a change to get underneath it: lots of snow lately.

[JohnC]

Stock answer: Check the ground (wire on the actuator.)

Yes, there is a switch in the axle that turns the light on when the axle engages.

[GMC Hauler]

Stock answer: Check the ground (wire on the actuator.)

Yes, there is a switch in the axle that turns the light on when the axle engages.

Where is that switch, it is it separate from the actuator unit or part of it?

[JohnC]

Where is that switch, it is it separate from the actuator unit or part of it?

Now you're making me think too much. Someone else can probably tell you for sure, but I'm pretty sure there's a switch in the axle that is activated when the collar slides far enough to lock the axle shaft to the side gear. Either way, it's not part of the actuator.

[Mike782]

Did you ever figure this out? I have a similar problem. Mine is slow to engage and disengage... however, it does engage (you can feel it) but the light sometimes does not come on right away (replaced the bulbs yesterday as they were burnt out) and it is very slow to disengage.

[GMC Hauler]

Did you ever figure this out? I have a similar problem. Mine is slow to engage and disengage... however, it does engage (you can feel it) but the light sometimes does not come on right away (replaced the bulbs yesterday as they were burnt out) and it is very slow to disengage.

Same issues, but have not had a chance to work on it. Work has me real busy here. If you figure it out, please post.

[6.5 Detroit Diesel]

the switch is a little plug located in the side of the carrier housing. there should be a black and white wire running to it. i can't remember but i think it unplugs. you will need a big wrench, but back it out of there and test it. it can slowly go out, and that will result in extended wait periods for the 4X to engage. when power goes to this little unit, it extends out, and pushs the gears into place. kinda a crappy system, but easy enough to work on. replacement up here for the actuator is around $200. we've just went to the scrap yard and pulled out unit for a few bucks and put them in.

[6.5 Detroit Diesel]

oh, and i can't remember finding a switch anywhere. i think pushing the stick into 4 wheel completes the circuit? don't know for sure though.

[JohnC]

If you have the original thermal actuator:

Putting the lever into 4WD engages the front drive shaft in the transfer case, sends power to the actuator which heats up and extends much like a thermostat and pushes the "shift fork" inside the axle to lock the half shaft to the side gear, and turns on the indicator light for the front drive shaft on the console. When the front axle is engaged the mystery switch closes and turns the light on the console for the front axle (I think).

[GMC Hauler]

We'll, I did not do anything to it. I usually exercise the unit once a month. But..... I was on a 6 month deployment. So, the unit did not get exercised. I used it several times in the New England winters so far this winter, and now it instantly disengages and engages. No more problems.

I have the newer motor model. Replaced it several years ago. Guess it even needs exercising.

[Robyn]

If your truck had the original thermal actuator and was retrofitted to the servo unit then, there was a refit harness to make it all work. The trucks that came with the servo motor from GM did not have the switch on the front end, but instead the light is controlled by the servo motor.

The T case switch can get hinky at times and or the servo motors can quit.

I would stuff in a fresh servo when you can as its likely the cause of the issue.


Robyn

[GMC Hauler]

If your truck had the original thermal actuator and was retrofitted to the servo unit then, there was a refit harness to make it all work. The trucks that came with the servo motor from GM did not have the switch on the front end, but instead the light is controlled by the servo motor.

The T case switch can get hinky at times and or the servo motors can quit.

I would stuff in a fresh servo when you can as its likely the cause of the issue.


Robyn

I had the thermal actuator originally, and installed the servo and harness.

When the front axle was not engaged, but the T case was in 4WD, I checked power going to the servo. There was power and a proper ground present, so I ruled out the switch on the transfer case and the wiring at that point.

I will keep an eye on that servo. It must be 100%, cannot wait on it to fail when I need it the most.