Im having trouble with my 1994 gmc jimmy and the four wheel drive. When I put it in 4wd and spin wheels the front end sounds like a hub is bad but the front wheels don't spin The front driveshaft does

if you put it in 4wd and your front drive shaft is spinning but your front tires won't. that sounds like an actuator issue. the 4wd actuator is what locks your front differential into place. and electronic signal is sent from your t-case telling it to go into 4wd. as for your bad hub. im hoping thats not related. there is generally a hum that comes from these t-cases when locked into 4wd. if you believe it to be louder then normal check your fluid levels in your t-case and front differential. the actuator is connected into your front differential on the passenger side. take it out of the diff and let it hang while connected. then have someone in the truck and put it in 4x4 if the actuator doesn't move. thats your problem especially if it vibrates or makes noise. if it does move that it not your problem. in which case it could be your gears in the diff. or a t-case problem

it your actuator doesnt engage also look underneath your battery plate. you will have to remove your battery and the 2 bolts that hold down the plate underneath you will find a vacuum diaphragm if the is moving properly and your actuator is not it is the actuator or a vacuum leak

I have already replaced the vaccuum switch on the tcase and the actuator under the battery all is workin as it should. I hit the button it flashes a couple times and locks in. Same for low. It almost feels like the front wants to lock in but kinda pops back out. And it's not an average hymn either. The 4wd worked fine when I bought the truck but when I went to go use it one day it just didn't work. Replaced the switch then the actuator. And now I put it in 4 and it seems like the cable isn't pulling the pin in the front diff all the way. The cable is fine I have removed it at both ends and it's intact with no lag. I just don't know how exactly the front diff works in these. Only had the truck a few months. Sometimes I can bang on the front diff with a hammer and when I get back in the truck it seems to be locked in but just pops right back out. I'm about tosell this piece if iI can't figure it out

take a look at this video i stubbled upon. even though your cable moves.. remember all this is being controlled by vacuum which has less power then your hand if the cable is binded or rusted and does not move 100 percent free it will cause problems. other then this cable im affraid the problem is within the gears of your differential http://shelf3d.com/JOmD7dGP8AU#How To Fix 4WD Front Axle Cable GMC Sonoma Chevy Blazer 1AAuto.com