Toyota Repair: Toyota Front wheels not working in 4 wheel drive, vacuum pipes, vacuum lines

Question
I have a 92 toyota ext-cab pickup that has 128000 miles with a 5 speed trany. When I put it in 4 wheel drive low the truck will drive real slow like it's in 4 wheel drive but the front wheels will not engauge. The reason I know this is I had it in 4 wheel drive and tried to go up a grassy hill and the rear wheel started spinning but the front wheel did nothing.It has the auto-lock front hubs and the 4X4 light doesn't come on the dashboard when I put it in 4 wheel drive.

Answer
Check the actuator on the front differential, this is what locks the hubs internally to turn the front wheels, there are two vacuum lines that come from a solenoid, a common problem is that the vacuum pipes get clogged up at the actuator, remove the actuator and clean out the vac pipes, the switch that turns on the 4x4 light is on this actuator this is whay the light on the dash doesn't come on. If the pipes can't be cleaned out or if the vac diaphragm is leaking the actuator has to be replaced.