My buddy has a '96 GMC with the push-button 4wd. When he tries to engage it the light on the button will only blink and it will not engage. It happens on both 4-high and 4-lo. Does anyone know what this means?? I looked at the tcase and there is no manual lever to engage it either. There must be some electric actuator to engage it??

did you try puting it in neutral than switching it to 4x4

My guess is your actuator in the front end is shot.

yeah we did try it in Nuetral but still no go. Where is the actuator on the case?? and how hard is it to replace??
I've never dealt with the electronic cases before.

It may be the actuator and it's easy to check. The actuator screws into the front diff housing. Unplug it and unscrew the actuator from the housing. Plug it back in and put the truck in 4WD. The actuator should get a little excited and grow about 3/4 inch or so. It takes a few seconds since oil heats up and causes the expansion. If you want 4WD now and don't want to wait for a new actuator you can stick a little plastic or wood plug 3/4 long in and then screw the old actuator back in. This will keep the front alxe locked in all the time. It won't hurt anything but it'll be a tad harder on gas, like the old rigs were before freewheeling hubs. I live in the North and we put our trucks in 4WD in november and leave 'em there 'till may so we go through a lot of actuators. Most guys here have plugs installed like me. I have a 94 GMC Sierra with thelever on the floor. Normally when you engage the lever you have to wait until the actuator heats up before it'll lock in. When it's -40 this can take a while. With the plug instead of the actuator, it's nearly instant.

another option that doesnt involve putting foreign materials into the differential, is the posi-lok. it is a manual version of the thermal actuator. GM switched from the thermal version to an electric version a few years ago, but its still an electric component down i nthe mud, snow and salt....not the place, i want something electric. so i got a posi-lok. it allows you to engagethe t-case, and then at your leisure you can engage the front diff. this allows you to operate in 2WD low range as well. this might be a good option for you. price is very comparable to factory replacemnt

Sounds good. Is it cable operated? I heard of one that used a nitrogen cylinder to blast the collar over locking the shafts together. Where did you get it?

yes the posilok is cable actuated, manual of course. no there is no bursting nitrogen fancy new fangled stuff to it. [img]images/graemlins/grin.gif[/img]