Question about 4WD on Newer Vehicles

[OffRoader93]

My girlfriends 94 Yukon's rearend blew up. So I thought I would just use 4H to limp it back to our shop. I got about 3 blocks and it just quit going. It seems like the transfer case is fine because it looks like both driveshafts spin freely. The CV joints up front seem to be alright. I heard from a couple of guys that if the rear isn't working right, the front wouldn't work either. I was just wondering if this is true. Is there a sensor or something that won't let 4WD work unless the rear is working? Any help would be great. Thanks a lot. Merry Christmas.

Brenton

 

[divorced]

I don't know about the Autotrack trucks, but on the regulat models there are no sensors, and the front differential has no idea what the back differential is doing. What do you mean by "it just quit going"? Is it possible the rear end is locked up and not allowing the vehicle to move?

 

[OffRoader93]

The vehicle can be pushed. It is not locked up. The driveshafts spin and nothing happens. The electronic engagement on the front differential sounds like it is working. Any help would be great. Thanks.

Brenton

 

[MTMike]

Aren't the hubs on those vacuum actuated? I drove an S-10 Blazer 1 winter and I lost 4WD on it and coudln't figure it out, so I took it into a shop and found the acuator valve that controls the vacuum to the hubs wasn't working, thus the hubs weren't locking in.

It sounds something similar to that to me.

Mike

 

[muddybuddy]

i dont think autotrac was out yet in '94. what mike is sayin makes sense to me.

 

[resurrected_jimmy]

tahoe's don't have hubs, I'm going with CAD (center axle disconnect)failure

 

[OffRoader93]

What fails with the CAD? Thanks.

Brenton

 

[resurrected_jimmy]

the CAD uses a heated gas actuator (early style) that pulls a locking collar into place on the two halves of the long side shaft in order to engage the front axle. The actuator fails and you cannot get the front axle to engage. It is my understanding that the replacement actuators are electric and don't suffer this problem. You can see CAD on the back side of the front end housing

 

[OffRoader93]

I am pretty sure this Yukon has the electronic one. It sounds like it is working when I shift it. I took the actuator out and manual pushed in there with a extension and it still doesn't seem to engage. Does the driveshaft or axles have to be spinning with the vehicle moving under power for the 4WD to engage? Thanks for all the help.

Brenton