4WD issue

[archerwon22]

91 Jimmy wants to engage in 4wd. It has a floor shifter with window that illuminates wheels when in 4wd. Wheels illuminated all the time, but the light that shows 2wd is off.
I suspect a vacuum leak. When I accelerate the wheel light goes off until I lift off the gas pedal. When I am on the highway at speeds over 40mph it will try to engage 4wd and start making a roar/whine noise. I let off the pedal and giggle the 4wd shifter and it stops.
Any suggestions?

[MT-2500]

Go over vacuum lines and check front axle for locking in good.

[vtmecheng]

1) STOP DRIVING THIS VEHICLE RIGHT NOW!!!! You are going to blow up your front differential or transfer case, not that this might happen but it will happen.

2) It is probably the 4x4 vacuum actuator switch, mine did the same thing and didn't want to fully disengage the front differential. The light that illuminates the front wheels when in 4wd is connected to the front differential, when it is lit the front differential is engaged. The vacuum switch is located on the to side of your transfer case and has three vacuum hoses connected to it. Just remove the three hoses (I think they all come off together but could be wrong), unscrew it from the transfer case, and replace it.

[archerwon22]

just bought the switch along with all new vacuum hoses. Will let you know how it does..... thanks a million!!!!!!!!!!!!!!!!!!!

[archerwon22]

Thanks guys....... Replaced the vacuum actuator switch and all vacuum lines for good measure and it solved the problem.......

[MT-2500]

You are welcome and.
Thanks for posting back with the fix and how it went.
Good Luck
MT