92 4X4 Front Diff. Problems

The actuator pin where the cable attaches on the diff. is stuck in 2 wheel drive. I need info on the internal workings of the front diff and what may be stuck or broken inside. Prior to this actuator sticking I was having a hard time getting the front diff. to engage and staying engaged. I purchased this truck less than one year ago and at that time the tranfer case vacum switch was stuck in the engaged position. I replaced the vacum switch and the cable shortly after buying the truck. After replacing these items actuation was no problem but only tried a couple times on gravel and did not try to actuate again until the snow started flying this winter.

Thanks In Advance...Sean

check tpo see if you are actually getting vaccume pressure it the diaphram just before the cable if not theres your problem