I have a 2001 Supercab Sport XL 4x4 4.6L with the Manual Shifter on the floor. It also has a body lift and the 3'' extension has been added to the shifter. The other day I had to lock it in 4-Low, after slowly trying to accelerate I noticed it wasn't locked in. I tried again and no go, so I put it back in neutral and got out of the loose sand. I got on flat ground and tried 4-Low again, it went in but when accelerating/decelerating I could here and feel the front axles disengaging when decelerating it would also do this with a moderate turn left or right. It almost sounds like a pop/clunk when it disengages. The truck has 217,000 miles on it and runs great, 4x4 has never given me any issues in the 8 years I've owned the truck. What are some possible things to look for here?

Thank you for any advice,
David Smith

 

The vacuum actuator slides a sleeve to lock up the front axle.
The lock up must have some issue from wear or is getting vacuum to disengage or the actuator is not holding.
Good luck.

 

Thanks Bluegrass. How would I check for this failure in the vacuum lines or in the actuator itself or both?

 

Depending on how safe you feel doing this, have some one you trust, operate the 4wd switch with the emergency brake on and foot hard on brake while you get under the front and take a look at the actuator operation.
Vacuum is applied to one side of the actuator to pull, moving the link inside the axle housing.
The disengage is applying vacuum to the other port to pull the link back.
Is the link moving, is it restricted, does in need lubricant applied?
You can use a hand vacuum pump to do the same without running the engine, right at the actuator ports after the lines are removed.
.
If you do it with an assistant be sure he understands the truck cannot move when doing the testing and leave the throttle alone, for your safety and communicate so each can hear the other over the engine idle noise.
Good luck.

 

Thanks again for the great info Bluegrass, I'll dive into this tomorrow! Would this be any different given that it has the manual 4x4 shifter and not the 4x4 switch?

 

No, the front axle operation is the same for both.

 

Ok, so with a little inspection and testing, the actuator does move/engage but it inly moves approximately 3/16 - 1/4 of an inch when going from 2h to 4h/4l. I noticed when the truck wasn't running that when I pushed on the actuator it will move just a hair but feel kinda crusty. Is it safe to say that this would be causing it not lock the front axle fully? It will lock it in but when in tight turns, bumps and deceleration I can here/feel it popping and trying to grab.

Thanks for all the advice thus far!

 

It has to move more than 1/4".
Better move it by hand and apply some spray-on lube to free it up until you feel it engage much more.
1/4" is not enough sleeve and spline engagement to hold the torque needed to keep it against the weight of the truck, power applied and any other movements.
It needs this even more in low range.
Good luck.

 

After pulling the rubber cover off of the actuator rod putting a little lubricant on it and trying to move it with a screwdriver, I can feel it loosening up but still not enough to fully engage it. So the the next task is replace it. I noticed the pin holding the connecting rod that goes into the differential, does this need to be removed in order to take off the actuator? How do you remove the actuator other than the retaining clip?