4x4 HELP

[fiffer]

My 4wd has left me stranded twice in the last month. It just doesn't engage. The light reads accurately and I have tried both auto and manual lock on the hubs. I think It is not engaging in the transfer case. Both times I was able toget it to engage after the fact by driving and switching to 4wd but for some reason it doesn't engage when sitting still. It also does not stay engaged but I'm not sure when it disengages itself(possibly when I shut the truck off)

Any help would be appreciated. I'm leaning towards vacuum or this electric motor that engages the transfer case but I do not fully understand the theory of operation.

Thanks,
Chris

[fiffer]

No one knows the 4x4 theory of operation and can offer me some insight? I would really appreciate it.

[bigric]

Start simple--is the front driveshaft turning the times that you think it's not engaging? If so, check all your vacuum lines and seals.

If not, pull the electric motor off of the transfer case and see where the selector is pointing. If it's out of range, the stop bushing in the motor may have rotted out and can be repaired with some fuel line.

[fiffer]

Thanks for the tips. I'll start there.

[bigric]

If it's anything like the 1356 cases, here are some pictures I took a long time ago:

http://fullsizebronco.com/forum/showthread.php?t=30512

[twoicebergs]

There are 3 things that must happen to engage and get the 4x4 light. Switch position, vacuum/hub lock, and engagement via shift motor position. It will try for about 20-30 seconds and time out if it can't engage. It is quite common for the shift motor to go bad. Look on eBay for a new one. Try shifting from a stop, sometimes the ESOF will work better 10 mph or less. The older they are, the more likely to fail or work slowly, especially in really cold weather.

The next problem is the mechanism in the transfer case being dirty or worn. You could try to flush the T/C with a cleaner then put in new fluid.