ok i have a 92 gmc 1500 with auto locking hubs, and i tried to use the 4wheel the other day, i threw it in neutral and put the transfer in 4 high, the stick feels like it engages but front wheels DO NOT engage, on the flipside, when i put it 4 LO, it goes in and the 4 wheel works. as a side note when i put the transfer in neutral, you can here a faint grinding noise. is it possible that the linkage is maybe off? or are there seperate signals for the 4 high and 4 lo to engage the hubs? any advice would be golden Thanks.
pewter is your man on this question
I’m not sure what GMC was using. I had a '90 4Runner that had a similar problem and used vacuum lines to engage the 4wd. Turns out they had all been ruptured and it was a simple fix. Just something to consider. I never tried putting the transfer in neutral though, so I can’t tell you anything there.
Fullsize GM trucks used a fully electronic front axle. They are plagued with issues & are relatively simple to fix. There were at least 3 factory upgrades to the front axle solenoid, and they still have issues.
I have seen on more than one occasion that the switch on the transfer case is bad & will not allow the front axle to engage. You can test it easily with a continuity tester. It should be open when in 2wd & closed in 4wd. If the 4wd shifter isn’t adjusted properly, the switch may not engage either. This switch needs to be closed to tell the front axle solenoid to engage. I would look here first before spending any $$. A simple toggle switch can bypass it for a temp fix.