I obtained a 99 blazer ls 4x4 4 door about a month and a half ago. When I was driving down the road it started making a wierd humming/grinding noise which was remedied by unplugging a vacuum line under the hood. Now, I don't have 4wd at all, even with the line connected. My lights for the control don't even light up anymore. Any ideas on what the problem may be?

 

3 button or 4 button 4WD dash switch? Sounds like you've got constant vacuum going to the 4WD actuator under the battery tray. A vacuum switch is probably stuck open.

 

3 button, no auto 4x4 button

 

The humming/grinding was coming from the axle clutch on the right front axle. Disconnecting the vacuum line removed vacuum from the axle actuator under the battery tray which totally desengaged the axle clutch. As a result, no 4WD and no grinding noise. Are there any warning lights on the dash indicating a problem with the 4WD?

 

For a 3-button switch, all you'd get would be flashing indicator lights. I would start with the transfer case vacuum switch. Sounds like it's stuck open. Replace with GM part...aftermarket didn't work well for me.

 

the only light that I have on the dash is the abs light, I thought that it may be the switch but I couldn't figure out why it would be trying to engage all the time before and now, not trying to at all.

 

not sure if the vacuum solenoid on the firewall is used for a '99. For my 2001 it was on the firewall above the distributor. It stick open some tomes giving me vacuum to the 4WD acctuator, or at time closed with no vacuum to actuator and would not engage the 4WD. Bypass this solenoid with engine vacuum and see if it engages the actuator. Sounds like you are getting partial engine vacuum to the actuator all the time.

 

I am getting constant vaccuum and ill check to see if I have that solenoid.

 

There is either a solenoid on the firewall:




or a vacuum switch on the transfer case:





which ever one you have, that's the problem.

 

Okay I have no solenoid on the firewall. Is the switch on top of the transfer case or possibly in an easier location to get to?