Just put this truck back on the road after being parked since 2008. While driving at 45 mph, transfer case engaged and is locked in 4wd lo. I did notice a pop about a minute after I started the truck. Drove approx. 5 miles. Transfer case engaged and chirped the back tires, slowed speed to about 5mph. Having it towed home. I'm thinking shift motor, but welcome any and all ideas. Thanks

 

What do you mean the "transfer case engaged"? Do you mean it just did this on it's own? Out of nowhere?

 

Yes, the truck shifted into 4lo while I was driving at 45 mph. No controls were touched. No fan no radio no 4wd selector. It did wake me up though. Not sure why it shifted, now is stuck in 4 lo

 

The only remotely possible way is the GEM module has been getting wet from a windshield leak and corroded the circuit board.
It's behind the dash fuse panel.
Reason is, you know it takes the shifter in neutral, truck stopped and foot on brake to get it into 4L.
Certainly the case motor would have to run to it's second position to engage low range and change the engine shift and rpm functions because that is the only way the PCM can be signaled to do so.

Good luck.

 

pull the shift motor, move it back to HI, reinstall and leave the wire harness off for now..... back on the road.

 

Should I disconnect the jack shaft, or would that make a difference?

 

if the transfer case motor is in HI and the wires are lifted , it can not signal the next step to signal the axle to engage....... if you want, you can pull the vacuum hoses off the front differential pumpkin cylinder and then it can not engage... make sure it is disengaged before you pull the hoses... or move the rod by hand afterward.. jack one tire off the ground and try to rotate it to see that the driveshaft is disengaged from the axle and transfer case........... it does not have to be removed.

 

You realize two things happen when you put the truck in 4 x 4........ first the transfer case motor moves to engage the driveshaft......... then two solenoids on the fire wall are signaled to send vacuum to the front axle to pull the engagement pin "in" or "OUT" to engage the driveshaft to the axle shafts.

 

thanks guys. All good info. It sure gives me something to trouble shoot with. It really. Baffles me how it went from 2wd to 4 low. The selector does not work, only clicks under the dash. Does not indicate that 4wd is selected. Tried backing out of it but the axle is still engaged. I did here a pop under the truck right after I started it and then drove 4-5 miles before it locked up. I recently replaced the upper and lower ball joints. And serviced the transfer case and transmission . ( filter and fluid). is there anything I may have done to cause this. This truck has the CV axle front differential. Just unbolt the axle from the differential and remove it. I did not notice any vacuum hoses, while I was under there, but will look again.

 

Leave the front axles alone.
Remove the case motor and turn the shaft back to 2wd and reinstall the motor.
Leave the electric connector off until you get to look for the problem.
This should also disconnect the front drive.
Good luck

 

Thanks bluegrass and Steve. That's what I will do. Don't need the 4wd right now anyway. Hopefully the problem is something simple. Again thanks for the info

 

when the transfer case motor is off, plug it in and set it on the floor below the truck. Use the dash **** and select different HI- LO and see if it works.. Might just be in a bind, might be shorted out or burnt... but WHY did it move if you did not turn the **** ?

 

Hi Steve and Bluegrass 7, waiting on parts to arrive. I did remove the shift motor and put the transfer case Back in 2wd. The shift motor was froze up and would not move when the selector was operated. Ordered new motor, should be here by Friday. Also looked at the actuator. It seems to operate smoothly when I manually work the lever. Have not tested the vacuum yet. I'm on my way to buy a new vacuum pump. The rod is all the way in. Is this engaging the axle or disengaging the axle. Not sure what it looks like normally in 2wd.

 

I would be concerned about a ground out in the harness that could run the case motor independently of the GEM so look it over carefully.
If that should happen and the motor is powered up on a permeant basis it could ruin the motor.
Remember the power is applied to the motor through a fuse waiting for a ground 'from' any source and hopefully only from the GEM in a properly operating system..
The Actuator is an in out operation determined by vacuum applied to either sides port.
There is no auto return action on it.
It moves a collar inside the axle housing to spline two axle parts together.
You can check this by turning the wheels with the actuator engaged and note the results.
Good luck.

 

I think you can switch the vacuum lines and make the cylinder stroke.. one line always has vacuum on it, I believe.