Well my 4WD is not engaging on my 89 Sierra. The trasfer case and tranny are fine. When I go to engage it the 4WD light comes on and the front driveline coming from the transfer case locks but the front diff does nothing. I think the problem is coming from the front diff but dont know what could be broken inside? By the way my thermal actuator moves when I move the 4WD lever so I think that is fine. Thanks for the help in advance.

Just because the actuator moves, it doesn't mean that it is engaging anything. Tear it out and take a look inside. While you have it out, be sure to look at all of the parts. There is one washer in particular a buddy of mine changed out in his Sonoma, and it was the problem. I don't have the manual handy to tell you which one. Sorry.

Well I bought a new actuator from Car Quest a while back and it didn't solve the problem so thats why I don't thinks its the actuator. What else could be causing this?

heres what you do,listen closely. take a torch and cut out all the IFS shit and throw it in the back yard. then put a straight axle in. you wont be sorry,,,i sure aint
http://community.webshots.com/rz/r1/2/10/24/28421024YOkcZQHQwj_ph

Originally posted by GMC4X4Yota
Well my 4WD is not engaging on my 89 Sierra. The trasfer case and tranny are fine. When I go to engage it the 4WD light comes on and the front driveline coming from the transfer case locks but the front diff does nothing. I think the problem is coming from the front diff but dont know what could be broken inside? By the way my thermal actuator moves when I move the 4WD lever so I think that is fine. Thanks for the help in advance.


To check the front diff, engagage the 4x4 [with the key on]. and jack up the rear end a couple inches,turn the front driveshaft . If the truck moves its's not the diff. I'm thinking its probably either the actuator or something at the wheel itself. A dif would probably make a heck of a noise.

Are you talking about the front driveshaft coming out of the transfer case? Are you saying if I try this the front wheels will turn? If its not engaging then the front wheels wouldnt turn right? I am pretty sure my front driveshaft coming out of the transfer case is locking cause when I engage the 4wd and go you can see it turn but the front diff doesnt engage the wheels.

Originally posted by GODFATHER
something at the wheel itself.


There isn't anything at the wheel. It is direct drive from the hub flange on the front chunk out to the wheel. If something is broke in there, he's got more problems than just 4wheel drive not engaging! :eek:

Anyone else have any suggestions?

if you buy an actuator from gm ( which is who i would buy it from), you'll get an updated design and wiring harness. i've never seen one of those fail.
still, i'd jack up the truck and see what happens. you could have a bunk hub in the front and with an open diff, it'll never act like it's in 4wd.

ps: i almost forgot; check alll the fuses and your linkage at the t-case.
another common problem is that the early (like yours) t-case shift forks were stamped steel. these had a lot of problems and have since been updated to a cast aluminum unit.
have you drained the t-case to check it for damage?!:rasta: