C4 Transmission vacuum line issues

[Kkelsey]

I have a 1971 Bronco with a 3 speed transmission in it. I acquired a c4 transmission from a 73 or 74 bronco.
‘this transmission has a modulator with 2 Vacuum lines instead of 1.
I understand 1 goes directly to the intake manifold. Does it matter which one?
Also, where does the sec one go since my vehicle doesn’t have an EGR system on it?
should I replace the modulator with a yellow dot model with a single port?

thanks for the help.

 

[billh1289]

I swapped out the 2 port in my ‘73 for a single port with no issues fwiw.

 

[Broncobowsher]

Single port modulator is the better answer.

The just make it run, rear (outer) port to vacuum and leave the other open.

If I remember correctly, the second port went to emissions controls so it would still shift about right when there was little vacuum because the EGR was open. No emissions controls, no second port.

 

[Rustytruck]

have you done a compression test on all cylinders and a leak down test on all cylinders. when doing a vacuum test even though its low is the needle steady? these tests show the condition of the engine. have you pulled the plugs and taken a good look at them.