J Shifter Transfer case 4wd not engaging properly.

SIKHILUXSURF

SIKHILUXSURF

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Hey guys i have been searching to get some more answers to my 4wd issues but it seems everyone with issues seems to have it on limited models with push button 4wd. its been a few weeks and i notice it wont engage when i shift into 4hi, no binding when i turn either way full lock and no light on the dash when in 4wd or 4lo. i just can back from lunch earlier and decided to drive it in 4 high to see if it might kick in on a whim. when i got close to work the light turned on and i was applieding pressure to the transfer case shifter like it was going to pop out or something. and the light came on and i felt it in 4wd. when i let go of the shifter the light shut off and i wasnt sure it the 4hi was off again so i applied pressure to the j shifter again and the light came back on and i could feel binding when turning. question is is there some sort of sensor to the transfer case or on the transfer case that controls engagement? if so when is it located and is it something i can replace?
 
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First thing to do is verify if the T-case or ADD (front diff engagement) is the issue. On a J-shift, this is easy:

1. Put in 2wd.
2. Check that front propeller shaft spins by hand.
3. Engine off, engage J-shift in 4wd (check both H and L.) Shaft should lock up if T-case is good.

If it does lock up, then problem is in ADD system. Here is my routine for that. (Written based on my '99 J-shift, so should work for you.)

VSV’s/ADD
Don't guess at it, troubleshoot! Start at the twin VSV's (Vacuum Switching Valves) on the driver fender wall. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hose nipples on the VSV’s has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum going to one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator or the line to the diff. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay. (Mark the hoses first so you know which belongs where!)

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the TC, the switch on the TC, or the TC actuator, or its wiring back to the button (last two for non-J shift only). If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck. [Does not apply to '01-'02]
Click to expand...

Once you confirm the issue is the electrical signal to the VSV's does NOT switch, THEN you can think about those switches. You aren't there yet.
 
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So as I was driving home I tried to engage 4hi on and off and it starting to engage again but if I don't hold the the shifter in 4 hi the light shuts off on the dash and it pops out of 4hi. Do doesn't seem like the transfer case is bad since it still engages with me holding it in 4 hi to geek it activated. Could it be I have loose shifter link somewhere?
 
This was mentioned before I believe but.......

1) In park and selector in 2wd crawl under toy and verify front drive shaft spins freely by hand.
2) put selector in 4wdhi and crawl under and see if drive shaft still spins. If it does spin there is a problem with the linkage adjustment or something wrong or worn in the transfer case.......if it does not spin then the problem may be the limit stitch that detects that shifter position or the vacuum switches. But since you can get it to work holding the shifter............
 
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