4WD won't engage

danimal96 · March 3, 2015

I need some help guys.

I have a 1994 Sierra 3500 4x4 with 43000 miles.

4x4 was working fine, shut the truck off and 15 minutes later no 4x4.

Actuator works but replaced it anyway.

Indicator light next to the floor shifter does not light. Fuses are good.

Driveshaft from transfer case to front diff turns when engaged.

What should I check next?

Thanks

8.1HD/ALLISON · March 3, 2015

Been a while, but does that year have the vacuum switch on the transfer case ? Sends vacuum up to front axle actuator? May check vacuum lines and switch.

gmtech4 · March 4, 2015

I need some help guys.

I have a 1994 Sierra 3500 4x4 with 43000 miles.

4x4 was working fine, shut the truck off and 15 minutes later no 4x4.

Actuator works but replaced it anyway.

Indicator light next to the floor shifter does not light. Fuses are good.

Driveshaft from transfer case to front diff turns when engaged.

What should I check next?

Thanks

I doubt it has vacuum , that actuator closes a switch in the diff ,

You may have to have the frt right diff tube actuator assy removed and inspected by a tech unless you are VERY handy

Get a schematic / service information for the 16 yr old truck you have there

danimal96 · March 4, 2015

No vacuum switch.

If I raise the front end off the ground, I should be able to spin both front tires in 2WD.

When I shift to 4WD and drive, I shouldn't be able to turn either tire. Truck is not running.

If I can't turn the drivers side tire but can turn the passenger side, knowing that the actuator is working

can I assume there is a problem in the actuator assy?

00Silverado4x4 · March 4, 2015

I'm not real sure but because you don't have a locker in the front diff I think that you will always have one tire you can turn and one you can't while in 4wd. I could be wrong though.

8.1HD/ALLISON · March 5, 2015

Sounds right^. I must have been thinking of the blazers.

green85 · March 5, 2015

Im new to this but maybe someone can help.I drove my truck to work the other day and when I went to leave that evening all the lights on my 4wd selector seitch were on and it wouldn't go into 4wd.I tried to drive it but it was either bogging down,trying to go into 4wd on its own or transmission slipping.I tried over and over but still couldn't tell what it was actually doing.Then ther service 4wd light came on ,but I drove it on to the house and after I drove a mile it drove perfectly fine.Still won't lock in and lights still on,but not the service 4wd light.Im stomped on it and needing advice

gmtech4 · March 5, 2015

No vacuum switch.

If I raise the front end off the ground, I should be able to spin both front tires in 2WD.

When I shift to 4WD and drive, I shouldn't be able to turn either tire. Truck is not running.

If I can't turn the drivers side tire but can turn the passenger side, knowing that the actuator is working

can I assume there is a problem in the actuator assy?

Yes , you need to self diagnose , you need to check the switch on top of t case to see if the actuator is getting power

danimal96 · March 6, 2015

I took the actuator out, hooked it up, put the truck in 4WD and the actuator comes out so it is getting power. I got all 4 wheels off of the ground, started the truck, put it in 4WD and the front drive shaft spins but not the front wheels. The problem must be in the dirr.

gmtech4 · March 6, 2015

I took the actuator out, hooked it up, put the truck in 4WD and the actuator comes out so it is getting power. I got all 4 wheels off of the ground, started the truck, put it in 4WD and the front drive shaft spins but not the front wheels. The problem must be in the dirr.

With the actuator out look in the hole , insert an extension or something to push on the shft collar , rotate the tire to fully engage the collar , i

If that doesn't lock the frt you have problems