Hello,
new to the forms but have been on them a lot since I got my Jimmy. Very helpful info, thank all you experts for your advise.

Now to my issue,
I have been searching the forums and trying to find advice on where to go next to fix my 4WD from not engaging. I have the 3 push button. I have replaced all vacuum lines, the actuator is vacuuming and has no leaks from what I can see. I have also replaced the transfer case switch that was not working but did not fix the issue. I have lifted all 4 tires in the air, when I push 4wd lo in neutral, I can here the click from the kick side panel, I can hear the metal shift which seems like it goes into 4wd but when I shift into drive the 4wd lo light turns off and all lights on the push button stay off. It seems like it shifts into 4wd but no movement from the front wheels. I lowered the ride back down as I read from another post and only jacked up the front passenger tire, proceeded to put in neutral and 4wd lo but I can spin the tire freely so obviously it’s not in 4wd. I just don’t know where to go from here and any advise would be greatly appreciated.


Update - So to add to it, just tried to drive in 4lo and when I try to drive from a stop it’s almost like neutral burning, meaning it revs real high and than slams into gear but it doesn’t feel like 4lo, more like 2lo. The lights on the push buttons go from 4lo being light up to all the buttons not being light. I honestly don’t know where the problem is coming from

 

Im going to start by replacing the actuator cable with Dorman 600-601. While im down there i will have a look at the fork.

 

One jacked up wheel may spin freely if it's a ratchet differential instead of a posi or locker.

I dont know your vehicle but in my 4x4 blazer the wheel touching air spins when the other is on the ground because the spider gears shift.

4x4 systems also tend to need to turn for a while for the parts to mesh. They are not synchronized like a transmission and even my SM465 4 speed which has synchros must be rotated many turns to engage the synchro without the engine running. Thats not noticeable when the engine runs because the input shaft speed is same as the crank speed, several hundred rpm.

Also watch for weak vacuum signals to diaphragm sometimes they don't quite pull all the way. Leaks or debris in vacuim switches cause that. Don't run the vacuum source directly to a actuator if theres a restrictor in the system.

 

I don't like Dorman, I've had too many problems with their stuff already.

 

Yes Dorman stuff is cheap Chinese . I use Delco if possible. More expensive but it also costs to fix it twice!

 

Appreciate everyone’s reply’s. Yeah I got under there right now and it’s not the cable and the fork looks to pull about a 1/4” freely. Also tested with pulling from the other end so cables moving like it should. I’ll check the actuator again. I’m trying to rig it to stay on connected to the batteries with jumper cables and see if I can test the vacuum. I’m really hoping it’s just a weak vacuum or air leak somewhere because if not it’s going to be something a lot harder and time consuming to fix in this heat today haha 😂

Also going to try and wire the OBDII and see if it’s throwing codes for the 4x4. #5 and #13 is what I think I read it is.....

 

So no codes coming from odbii but they may have cleared since I had the battery off. Put Jimmy in neutral, pushed 4lo and it is locked in. Got underneath and I can try to move front driveshaft but it will not so I know it’s locked in. Has to be something with fork, vacuum or internal.
Is there anyway to test the 4x4 to make sure I got it working besides me getting stranded stuck in dirt again lol

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so I tested the acutuator, cable and vacuum seems all good. The motor is locking in and the it’s in 4 wheel. It’s almost like the hub isn’t engaging. Any help or suggestions would be appreciated 👍🏼

 

So I double and triple checked all vacuum lines. Checked the fork, checked the line. In the end I found a video on YouTube that was my fix. Sorry but I’m updating just in case anyone runs into the same issues I’ve had. Apparently when your vacuum switch on the transfer case goes out and your 4wd gets stuck on, the fork tries to force the gear into the drive to lock the hubs in and destroys the gear in the process. The replacement part I found was Dorman 600-561 and it involves taking down the axle to the transfer case in the passenger side to replace the gear. I’ll link to the YouTube video to give him credit and help for anyone else who runs into this issue. Thank you guys again!

 

Throwing in a Bravada axle eliminates everything you checked/replaced. One of the best upgrades I've done by far.

 

I have owned a 1990 s10 which was the best I owned and a 98 and now a 99 jimmy.My 90 gave me no issues but thanls to my divorce I had to sell it.90 too many issues and now I bought this jimmy in March with 195,000 cause the guy who owned it maintained it .Now I had issues with the 4x4.Mine you could hear engage but nothing really happening.Well long story short try a new selector 4x4 switch double check your.vacuum hoses .There tricky and I did have a vacuum leak going from the selector switxh down to the tra seer case..