The first time it was caused by old flaking hose connections at the vacuum pump and at the vacuum manifold by the brake booster. This time it was a cracked hose boot at the control box switch. I'm going to try some silicone on it until I can get a vaccuum harness. BTW, does anyone know a good source for that? I don't think that the dealers carry it anymore.

Also, what does the vaccuum switch near the passenger side kick panel control?

 

Found the problem. The hard plastic hose that runs from the main t-fitting along the firewall to the passenger side, and through the firewall to the climate control plenum was badly cracked-- it broke off in my hand a few inches forward of the firewall on the passenger side.

 

I had my vacuum line melt/collapse on itself about an inch from the firewall on my dually. Just cut the line and added a compression fitting, I was just worried about the line falling into the firewall, lol.

Glad to see you found the problem and was easy.

 

Thanks for the feedback guys!!

Well, what happened was we changed the hydroboost unit last Saturday, and in the process of getting the old one out and the new one in, we accidently pulled on the vaccuum t and the old line cracked as a result.

I was able to slide the rubber boot back onto what was left of the old line and reconnect it for the time being. However I will be buying some rubber vaccuum/washer hose and replace the old hard plastic line in the near future.

In case other problems occur under the dash, I also ordered the under-dash vaccuum harness while it's still available from the dealership. The $38.00 is worth it to me since the connectors and color-coded lines would be hard to replicate .