Vacuum lines for C4

[WG]

I am putting a C4 from a 73 Bronco in a 71 Bronco with a 74 302. It looks like there should be two vacuum lines on the modulator. I need to know where the line from each port on the modulator goes to get vacuum from the engine. I am not at all familiar with the C4 (more familiar with the old Ford-O-Matics). The 71 had no engine or trans - was a manual trans. I pulled the C4 from the 73 which had no engine. And the 302 had been connected to a 3 speed. So I have nothing to use as a reference. Any help will be greatly appreciated.

 

[jckkys]

Just get a yellow stripe vacuum modulator that only has 1 vacuum tube to full intake vacuum at the tree behind the carb. A '71 would have no need for the '73/'74 2 tube modulator.

 

[Broncobowsher]

The 2-port is a bastard that was made to work with emissions systems that had un-natural vacuum signals.

The single port modulator is what you need. That just goes up to a manifold vacuum port (a single runner of the intake is just fine). Doesn't flow anything, just senses vacuum/load.

If you are trying to drive it before getting the single port, I believe hooking up the rear port to vacuum and leaving the front port open (vented) it should at least drive around and shift.

 

[luke]

Yep. Single port.