Hubs not locking in 4WD

TeamGreen · November 15, 2001

On my 89 Sierra my hubs are not locking when I put it into 4WD. I asked some people in my auto class and at the local dunes about it. They said it was the actuator. So I went and bought a new one and installed it but the 4WD still doesnt work. The front driveline locks but the hubs don't. What could be wrong? Ive had so many probs with this truck and I take good care of it! I'll never by a used truck again.

November 15, 2001

By actuator, I am assuming you're talking about the thermal actuator on the front axle.

If that wasn't the problem, check for 12 volts dc to the actuator. if it is there, you must have a problem inside the housing(ouch!). If not, chase that wire back to the T-case. It may be broken or grounding out.

I couldn't find any of this wiring in my manual. I'll keep looking. Let me know how the wire check goes.

TeamGreen · November 15, 2001

Yeah I was talking about the thermal actuator right in front of the axle. I checked the DC output of the plug that goes to the actuator and it didn't even read a volt. There was very low voltage there and it kept slowly rising but for how long I waited it never even got close to a volt. My voltmeter is fine too cause I checked the voltage on my batt and it was about 13 volts. So there is a elctrical prob then or could the plugs be bad? Its weird cause the 4WD light comes on when I put it in 4 high but still it dosent engage.

95 Silverado · November 17, 2001

disconnect the actuator and apply 12 volts to it directly from the battery, if it engages then you will know the actuator and internal parts are working properly, I would suspect the transfer case switch or a wiring problem between it and the actuator. did you get another thermal actuator or did you buy the updated version. the updated actuator requires the wiring to be changed, but it is a better, more reliable actuator.

TeamGreen · November 21, 2001

Im not sure if I bought the new actuator or no but there wasnt enough voltage to see if it even worked. Ill try connect two wires from the batt to the actuator and see if that works.