I’m having an issue with the front diff actuator always being locked. I removed the battery and verified that there is always vacuum at the actuator. I removed the cable to make sure that wasn’t seized up. When I removed the vacuum line at the actuator it immediately released and opened up. Does anyone know what controls the vacuum to the front diff actuator? Thanks

 

Depends a bit on your year and type of transfer case.

On the later 2nd gen Blazers that have a 4-button controlled transfer case (with Auto-4WD), there is a dedicated vacuum line that runs up to the center, top of the firewall in the engine compartment and connects to a solenoid attached there. If has failed in the open/activated mode, then vacuum would be going to the front axle to engage the axle.

In my signature I have a link to a thread on replacing the vacuum hoses in my 99 with the four button transfer case. There you will find several diagrams.

If you do not have the 4-button transfer case, then the vacuum routing is a bit different. I'm sure someone else can help with that setup.

 

Mine’s an ‘01 and has the 4 button with auto button. I’ll look for that solenoid and check out the diagrams. Thanks. Fixing odds and ends on it before my son takes it back to college since Christmas break is just about over. We’ve owned it for about 17 years now. My son was 2 when we bought it. 😂

 

I bet the hoses are switched on the ports on the vacuum switch on the firewall next to the distributor. A specific port is used to bleed off pressure when 4WD is not in use, otherwise vacuum is trapped when the switch closes. At one time I had the same issue with my 4-button 2001. Just change the hoses on the switch and you should be golden.

 

You were right! At some point I must have reconnected them backwards. We ended up picking up a new vacuum switch because it wouldn't close enough to shut off the vacuum completely. Thanks to both of you for steering me in the right direction!

 

you are welcome