i have a 99 blazer and when i start the engine the diaphram pulls the cable to lock the front diff without putting it into 4wd. shouldnt it only move once 4wd is engaged? what is causing a constant vaccum on this diaphram what is needed to be replaced to fix this problem?

 

3 button switch or 4 buttons on the dash?

 

3 button

 

On the firewall, just about in the center, there is an electro vacuum switch that looks like this:

Unplug the electrical connector and see if it still applies vacuum to the actuator under the battery and pulls the cable.

 

if the vaccum does release does that mean theres a problem with this switch?

 

If the actuator still pulls in when you start the engine, the switch needs replacement.

 

i followedthe vaccum line from the diapham back and theres no switch on the firewall. it goes right to the transfer case

 

If that's the case, the switch on the transfer case is stuck and needs replacement. It's located on the driver side, inboard and slightly above the front output shaft. This is what the switch looks like: Dorman Help! 49315 - TRANSFER CASE SWITCH | O'Reilly Auto Parts

And this is where it's located:


You can use a 7/8" deep socket on a 3/8" drive ratchet to replace it. 15 minute job.

 

mine does have that switch on the transfer case i thought that might have been it but wasnt sure. thanks captain!

 

No problem, keep us posted with how it goes.