<font face="Comic Sans MS">Here is the part of the article I'm working on so far, yup it's copyrighted by me for now... haha [img]/wwwthreads_images/icons/wink.gif[/img] But anyhow, i haven't had a chance to test out the entire procedure on mine, but it should work ok for troubleshooting:
<blockquote><font size=1>In reply to:</font><hr>
Troubleshooting GM’s Vacuum Actuated Front Differential
Up to a certain point (which is noted at the appropriate location ), this file will work for any GM S/T series pickups that utilize a vacuum actuator to engage the front differential.
Step 1: Verify Vacuum Actuator’s operation
For this step you won’t need any tools. Open the hood, locate your vacuum actuator. If you are unsure of the location of the vacuum actuator on your truck, crawl under the truck, and locate the cable that runs to the front differential. It should either be on the passenger side fender, or under the battery tray on the passenger side, however yours may vary.
Now, have an assistant start the truck, and pull the transfer case lever (or press the appropriate button if you have an electronically shifted transfer case) into one of the 4 wheel drive positions (high or low), it shouldn’t matter which one. Observe the vacuum actuator.
If the vacuum actuator pulls the cable, your problem likely exists in the electric shift mechanism, the relay for it, or similar things (assuming you have an electrically shifting transfer case) or your transfer case shifter is out of adjustment. I do not know much of the intricate workings of the electric shift mechanism, and so I won’t be able to go into it any more than this.
If the vacuum actuator fails to pull the cable, proceed to the next step.
Step 2: Determine whether the transfer case actuator (or shifter) is actually engaging the front driveshaft.
If your vacuum actuator engaged the front differential, your problem is either the transfer case, or something inside the differential, the actual mechanism itself.
Step 2: Determine the Cause of the Vacuum Actuator not working.
Pull the cable by hand (in the direction of the rubber diaphragm) to ensure that the cable is not stuck in one position.
If the cable doesn’t move fairly easily (remember there should be a little tension), then there is likely either a problem with the cable itself, or a problem in the differential.
Sorry I didn't get back to you JR, but it didn't want to let me reply for some reason. Anywho, I'll let you know when that's about done...
---edited part here--- I don't know what I was thinking when I wrote that, it doesn't seem to make much sense, I'll try to dig up the updated file I had on my computer, the one that really does make sense, and post that. Sorry about that. But anyhow just make sure the actuator moves, make sure the vacuum lines to it are ok, make sure nothing is frozen in place because of the snow or ice, and the basic things like that, I'd say there's a very good chance that will help you solve your problem.
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