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1989 4WD Problem

Discussion in 'Chevy Trucks' started by Gmgbo, Nov 16, 2008.

  1. Gmgbo

    Gmgbo Senior Member
    Messages: 159

    I have a 1989 GMC 2500 6 lug that wont go into 4wd. Three years ago I replaced the actuator. The 4wd light is comming on, but the truck isnt engaged in 4wd. When the actuator went bad the light wouldnt come on.

    Any thoughts?
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    If the indicator light is illuminating..then the actuator, slide collar, shift fork, and related engagement components IN THE FRONT DIFF are likely working fine since the indicator light is tripped by the movement of the sliding collar/shift fork on the axle shaft.

    Raise the front tires off the ground and attempt to turn the front driveshaft by hand with the T-case in 4WD and the trans in park (of course). Can you turn the drive shaft?
  3. Gmgbo

    Gmgbo Senior Member
    Messages: 159

    I will try it today and let you know.....what are the possible problems?

    Sometimes the engagment light flashes on and off
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    There's a red flag right there, your only getting partial engagement in the front axle disconnect for one reason or another. Could be many causes...weak actuator, worn engagement ring, broken spring, damaged clutch fork...poor electrical connection, defective switch on the T-case....

    Need to do a much deeper diagnosis... I'd start with getting all four wheels in the air and see if the front axle actually is, and is, staying engaged.
  5. Cooter24

    Cooter24 Senior Member
    from NE Iowa
    Messages: 268

    These electric actuators are junk. I had an 89 Chevy 2500 that I replaced several times before wising up and replacing it with a Posi-Lock brand (I think) actuator. Best investment ever for it. Still needed to shift transfer case, and also now a separate cable that pushed in the axle housing. Easy to install and no more waiting for the thing to engage.