Are you asking about the pumps or the vacuum motors? Vacuum motors have one hose connection and the pumps have two. If you want good dependable action, go electric.

Here is the theory in the shop manual. Shop Manual Explanation

Last edited by truckernix; 03/18/2015 1:07 PM.
1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!