2000 5spd JShifter 4wd not engaging

[cosmo4r]

Little bit of snow came down few weeks ago and made me realize my 4wd wasn't working. I have a 2000 5psd with Jshifter (no multimode).

4wd light never came on, 4Low seems to work but not 4Hi. Is that possible? Snow has since melted so hard for me to test but I'm pretty sure 4Hi is not engaging.

I'm confused, does my truck have the VSV and ADD? If the transfer case lever physically moves is that not all there is to it?

Thx

 

[dmppdx]

Little bit of snow came down few weeks ago and made me realize my 4wd wasn't working. I have a 2000 5psd with Jshifter (no multimode).

4wd light never came on, 4Low seems to work but not 4Hi. Is that possible? Snow has since melted so hard for me to test but I'm pretty sure 4Hi is not engaging.

I'm confused, does my truck have the VSV and ADD? If the transfer case lever physically moves is that not all there is to it?

Thx

In addition to the transfer case shifting into 4wd, the front differential needs to engage and its the vacuum controlled ADD that does that. I would guess its the 4wd switch on the transfer case that is bad since that tells the ADD to engage the differential and the 4wd light won't come on unless the differential is engaged.

Also, I believe 2000 models without multimode had a jshift, but the actual engagement of the 4wd wasn't through the actual lever, it was an electronic module similar to what the multimode had. That might be bad also. When you say 4Low is working is it actually engaging the front wheels in 4Low, or you can just move the transfer case to 4Low and the gearing changes? I don't believe the Add will engage even in 4Low without the 4wd switch working even if you move into 4low.

 

[MaineRunna]

It is in 4wd because it is a manual shift transfer case, it's just that your front axle isn't locking. It could be due to a faulty shift position switch on the transfer case, a bad automatic differential disconnect vacuum switching valve (ADD VSV) or just one the vacuum hoses being disconnected. Could also be the ADD actuator itself or wiring. Probably not any kind of a module problem

 

[pluton]

On a warmer day(if any) I would try to warm up the front diff and see if the ADD engages after repeated tries. It may be gummed up. You can, while driving the truck along a paved road in a straight line, repeatedly engage and disengage the front drive.
Alternatively, get the FSM and go through the checks for the front drive engagement. Could be a cracked vacuum line or other small thing.

 

[TheDurk]

The first test is find the twin VSVs and swap the two lower hoses going down to the diff. If that puts you in 4WD, your problem is electrical, or the 4WD VSV is toast. If it does not, the problem is in the vacuum lines, including possibly the one-way valve or the reservoir in the fender, or the front diff actuator. Remember, or better yet label, the hoses' position so you can put them back the way they are supposed to be.

This is also a good trick to get you in 4WD in an emergency situation when the electrical part of the system isn't working and you need that traction.

 

[2TH4IST]

Check the front diff detent switch, and the 3 detent switches on the t-case (by the j shifter). They can get gummed up and not work, thus the light not turning on. Cleaning them is freeish, besides the brake clean. Swapping the vacuum lines like thedurk said is a good test too. There is also a vacuum resiviour in drivers front wheel well that works the ADD actuator.