Hey Guys,

I've been reading up on 4WD problems lately and wanted some feedback on what I think my issue is.

Heres what I got: 2002 GMC Sonoma, 4x4 Crew Cab with G80 Rear Axle, 7.5" 3.73. 3 Button 4WD Switch.

Heres the symptoms: 4WD does not engage, however the transfer case does engage, the lights on the switch change successfully. Previously, I heard a whining sound, which I think may of been the cable partially engaged in the front axle. That seemed to go away after my mechanic replaced the passenger's side axle bearing and seal.

Heres what I replaced so far:

1. Vacuum Switch
2. Vacuum Actuator
3. Front Passenger Axle Bearing
4. Front Passenger Axle Seal

If you go under the truck, pull on the cable you can manually engage it and it seems to engage. I'm thinking its something in the front axle, or the cable is frozen, but that doesn't seem to make sense as you can pull on it a little and engage it.

Also, the vacuum actuator looks like it engages when you hit 4WD and pulls on the 4WD actuator cable.

Any ideas guys? Where should I go from here?

Also on another totally somewhat related note, any idea on the type of axle shaft I need for the rear driver's side axle? I need to replace mine as the one I have in there isn't the exact one that was in the truck which causes a few minor problems with the brake bridge hitting the rotor just very slightly.

 

I don't like to bump, but does anyone have any ideas? Or P/N? I don't like to throw more money at this POS, but I'm out of ideas.

 

Are you getting vacuum to the front axle when in 4wd (4HI or 4LO) and only when you are in 4wd?

Does your engagement cable move freely?

 

I can pull on the cable that goes up to the actuator with a pair of pliers, and it moves. As for the vacuum, last I checked yes, but since then I have done tons of work on it, so I will confirm it tomorrow.

 

Alright, I did some playing around with it today. I totally wanted to eliminate the possibility of vacuum, so I got a really long vacuum hose and tapped into the line that runs to the evap canister. I then ran that to the actuator. The actuator retracted, locked the hubs, put it in 4WD and it worked (or so it felt when I turned out of the driveway). However about a minute of working the fuse blew. I then replaced the vacuum line that ran from the actuator to the switch on the transfer case, but that didn't solve the problem.

What other lines should I replace? There appears to be 3 lines running to that switch. Which is the supply line?

 

The three lines are detailed in a number of vacuum schematics posted around the forum. I am sure there is one or two in the Tech Article (DIY) posts about the NP233/NV233 (same thing).