If the lite is on, and the t-case is in some flavor of 4x4, you have four wheel drive.

 

so Ive been driving my other truck and finally got some time to look at this.
my selector is in 4HI
the 4wd light is on
the front deiveshaft is locked
(vacuum lines for 4wd are reversed to bypass my broken and rusted selector switch)

i blocked the back wheels and gave it a go. the front wheels are 100% not turning. the back wheels will jump and try to shoot over the chocks i can watch the back wheel spin but the front ones do nothing.

so im positive the 4wd is not working its stuck in 2wd. ive done all the usual stuff like check t-case fluid etc.

the only thing i can think of is it has some thing to do with the reversing the vacuum lines to bypass the selector that is broken but i dont see how i guess.

ive check all the lines with a vacuum gauge and dont see any leaks or anything. kind of at a loss here not sure what I should check next...

 

Is the front driveshaft turning??

Jack up the passenger side front axle. With the t-case in 4hi, and the lite in the dash on, try and turn the passenger tire. You shouldn't be able to.... If you can, then the problem is within the cad. Might be a broken fork, slipped snap-ring, or a selection of other fun issues in there.

 

jacked up front passenger wheel
started it
shifted into 4hi
put it in park

wheel spins freely and the front driveshaft turns with the wheel.

side note i tried to check my 4LO and it wont shift into it.. i can go 2hi down to 4hi over to neutral but when i try to bring it down into 4LO it wont budge like its stuck...

ive read when you cant pull down into 4LO it could be because the linkage / selector bar or whatever thats called that connects the shifter to the trans case needs adjusting... would this explain my initial issue?

 

If true you have an internal problem in the t-case. Vacuum has absolutely zero to do with the 'case powering the front d/s. It's 100% mechanical and dictated by lever position.

Now I suppose it could also be a worn or disconnected linkage or linkage bushings.

I also saw your post about elevating the front right wheel and d/s turning. This means your CAD is engaging but the t-case is not in 4wd.

DO THIS TO BE POSITIVE:
- start truck
-leave your CAD hotwired so it's engaged
-pull lever to 4hi and be sure you're confident it's truly clicked into position
-drive forward say, 20'
-put vehicle in P or if manual N and set parking brake, leave it running although really it shouldn't matter
-repeat elevate right front wheel and spin. Front d/s should NOT spin because it should be LOCKED (basically tied together with the rear d/s) if t-case is truly in 4wd.

If it's not working next inspect all linkages and linkage bushings/pivots. If nothing obvious, disconnect linkage at t-case and see if you can click it to a spot where front d/s engages. You may need to use a pry bar or pliers or other mechanical advantage to move the shifter. If you can find 4hi, compare where it is vs where the shifter puts it and if a discrepancy, WHY?

If you're unable to get 4hi (or 4lo I suppose) manually, it's probably time to yank the 'case and open 'er up.....but this is the final step after exhausting all other troubleshooting

 

thanks! ill give it a try in a few minutes. I inly have 1 question.

when shifting into 4hi how do I know if its “clicked” into 4wd? should i actually hear a click or feel a click through the shifter? when i pull the shifter it moves but i never hear or feel anything to indicate its “clicked” per se...

 

Should feel the notch in the shifter.

 

How easy is it to put into 4x4? Shouldn't be super tough, but you should certainly be able to tell by feel that it is now in a different position.

 

ok yea i can feel it in the 4hi notch and it stays put.
i can also slide it to the right from there like normal to go into N and 4LO it just wont go down into N or 4LO once slid to the right.

 

its slides easy like butter and I can feel the notch