Just want to start off by thanking everyone on this board for the great info!

I have this 04 blazer 4dr 4wd 4.3 with 3 button NP233 almost 150k miles and runs pretty good. First got it in slightly neglected condition in October and have been gradually getting everything up to good working order.

Started off with having to replace the front driveshaft due to a bad CV joint. Kinda expensive, but not difficult. Doing this repair, I noticed that the front diff/drivetrain/hubs were always engaged. After checking the vacuum diaphram and cable, I discovered that the vacuum transfer case switch was bad. After replacing the switch, the front hubs will not engage at all! I have checked and double checked all of the lines, connections and hoses. Using a MightyVac I can pull vacuum towards the actuator and get the hubs to engage/disengage, have tried this at the the actuator itself, and at the hose connector at the switch. Also getting 20-25 inches of vacuum at the switch, plenty of vacuum. Not getting any vacuum from the switch when in 4wd at the actuator. No codes from the TCCM. Dash switch functions normally. Can hear the T-case engage from 2-4wd and 4-2wd, 4-lo works as well. Had the Blazer up on 4 jackstands. In 2wd, rears turn only, in 4 hi and lo rears turn only, but front driveshaft also spins.

All of that tells me that the problem lies in the vacuum switch, even though it is new. Removed the new switch, inspected and found nothing wrong. Found witness marks on the button end that showed that the switch was being engaged by the t-case, but still no hub engagment. Tried a second replacement switch, still no 4wd. At a loss now as to what could be causing the problem. We got a ton of snow coming and would like my 4wd back.

Is there any known issues with the Dorman replacement vacuum switch? Do I need to get a Delco/GM part? Now considering alternative manual hub engagement methods. Anyone know what vacuum solenoid to get?

Any help much appreciated.