88 Chevy 1/2 ton 4x4 trouble

Moline_guy · Dec 28, 2009

Went to use the pick up today and the 4wd wont engage. Light on console doesnt light, checked the wires underneath and everything appears to be hooked up. Looked at the fuse panel but didnt see one listed for the 4wd. We last drove it Saturday and used the 4wd to get through some drifts and it was engaged then. Any ideas where to start or what it might be. Thanks for any help.

old · Dec 28, 2009

Check under the hood for some fuses may find one there that is bad. Also could be a bad relay. I am just going by educate guess on it but have seen problems like that on a friends truck

Anonymous-0 · Dec 28, 2009

Actuator on front axle .

Moline_guy · Dec 28, 2009

If its the actuator would the light on the console be off when the lever is engaged to 4wd but the front axle is not engaged.

Allan in NE · Dec 28, 2009

Hey Guy,

Ya kinda gotta follow the "train" on those ol' gals.

When you throw the lever, a contact switch on top of the transfer case sends voltage to the front axle actuator and also to an "engagement switch" built in to the front axle that will in turn send the voltage back again to the indicator light in the console when the actuator hits the end of it's stroke.

The whole she-bang starts at the fuse panel via the ignition switch and darned if I can remember that fuse, but it seems to me that it "shares" a label with another function on the '88 model.

Hope this helps 'some'. :>)

Allan

Allan in NE · Dec 28, 2009

Hey Guy,

Ya kinda gotta follow the "train" on those ol' gals.

When you throw the lever, a contact switch on top of the transfer case sends voltage to the front axle actuator and also to an "engagement switch" built in to the front axle that will in turn send the voltage back again to the indicator light in the console when the actuator hits the end of it's stroke.

The whole she-bang starts at the fuse panel via the ignition switch and darned if I can remember that fuse, but it seems to me that it "shares" a label with another function on the '88 model.

Hope this helps 'some'. :>)

Allan

Jon Hagen · Dec 28, 2009

There is a fuse in the panel for the front axle actuator in my 92 Chevy. quite large, I seem to remember about 15-20 amp.

I always hated that slow reacting thermal front actuator, mine shorted and blew the fuse.

I replaced the thermal actuator with the motor driven one used in later years, now instead of a 30 second or longer wait for the front axle to lock, it now locks up in about 2-3 seconds and stays locked even if you turn off the ignition for a while. Makes it the 4wd it should have been when new.
To fit the motor driven actuator, you also need a wiring harness and spacer kit.
Chevy makes the kit for 1/2 or light 3/4 ton axles, it will fit the HD 3/4 or 1 ton like mine if you grind the axle tube for motor clerence.

Goose · Dec 28, 2009

Had to have the actuator motor replaced on my '89 last year. As I recall, the light on the console goes by whether the 4wd is engaged or not, not by the position of the lever.

Got another problem with my '89, but I'll start another thread.

Anonymous-0 · Dec 28, 2009

You are correct, the light will not come on until the front end is locked in. If the light is not lit, the front end isn't locked in. When the lever is in the 4WD position, the only thing locked in for sure is the transfer case. Like someone said earlier, go to GM and buy the newer style. I think there might be an adapter you might have to buy to plug it in to the old harness too.

Lee in Iowa · Dec 28, 2009

I just got a posi-lock manual engagement kit with a cable for my 89, but I haven"t put it in yet, got tired of fixing the thermal actuator. Anybody else tried one of these? I thought it would be nice to go to the low side of the transfer case with out engaging the front end like when I"m backing in a loaded trailer on a hard surface.

MirageFlatter · Dec 28, 2009

Had the same problem with our '89 GMC, after #1 son was busting through snow drifts and corn stalks with it once. Easiest place to start looking is to see if the wires to the actuator on the front axle have become unplugged, it's a simple fix if they are. Then use a test light or meter to see if you have power to those wires, if not, then go looking for that blown fuse or circuit breaker. #1 son found those wires loose on ours, not unplugged, but the part on the actuator that they plug into broken out. Picked up a used one at the local salvage yard for about $10-$15 as I recall. Pretty simple fix, and no problems since. Good luck!! :wink:

Bob · Dec 29, 2009

The original actuator on the front axle is thermally operated. Basically, a heating element heats up a bulb with a wax pellet in it, just like a cooling system thermostat. When the wax melts and changes state, it expands and moves a plunger that forces the axle disconnect to engage.

They "die" with time.

GM and now the aftermarket has a replacement unit that is a little gearmotor/linear actuator.

It engages instantly, without the wait of the thermal unit.

You need the new-style actuator and a wiring harness kit. ANY GM dealer can help you, as well as any autoparts store worth a darn.

For example, Dorman and BWD have them.

Bob · Dec 29, 2009

P.s....

Dorman # for the actuator is 600-601 ($83 at RockAuto)

Dorman # for the harness is 600-600 ($42 at RockAuto)

88 Chevy 1/2 ton 4x4 trouble

Moline_guy

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old

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Anonymous-0

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Moline_guy

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Allan in NE

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Allan in NE

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Jon Hagen

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Goose

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Anonymous-0

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Lee in Iowa

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MirageFlatter

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Bob

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Bob

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