vacume mod

[COORS]

well I'm stumped on this and even the good old guys at autozone couldnt help............
I got a late model c4 (70-82 only reason i know is because of the filter) But the modulater has 2 vacume ports a 1/4 inch and a 1/8 inch, anyone know what the second ports for and where in the heck does it hook up??

[COORS]

everyone else must be stumped on this too

[Phillyfanfrombirth]

Sorry.

[COORS]

crap got excited when i seen a reply
I'm assumming its a secondary vacume since its smaller, just dont know why 70-82 c4 trannys gotta have two ports...

[7DMACH1]

Ok being a Ford parts Mgr for 35 years I've seen these listed but never saw one on a car. It is called an Altitude Compensating type. I think they were used one cars built for high altitude locations. I would get a standard valve and replace it. Don't know what the purpose of the other line is or where it goes. Hope this helps.

[Phillyfanfrombirth]

That's interesting... seeing Coors is in MO... don't think that would be necessary...

Good info.

[COORS]

home of st louis MO (home of that aweful budweiser and elevation under 1000 ft ) and when i bought the car originally in southern cal
all the parts stores in both states have the same vacume mod..........


the 70 to 82 C4 is a better tranny because of the 26 spline but what the hell is the second vacume port is for?????

[Phillyfanfrombirth]

Might sound crazy...

But any chance that this is something to do with an early model cruise control?

[7DMACH1]

Thought I explained it???

[COORS]

they dont sell any standard modulators for it, all of them have 2 ports sticking out

[Kisner]

I had the same question 4 years ago. When I got our 68, it also had a late model C-4 tranny in it with the same modulator. The previous owner had about a 4-inch tube on the other port going nowhere (open). I was afraid to plug it or remove the tube, since I had no clue what it was for, so I just left it hanging there. Tranny runs great so I haven't messed with it since. But, I would still love to know what it was originally for, or if I should cap it.

[COORS]

the smaller port or the larger port?

[Kisner]

The open tube (about 4 inches long going nowhere) is hooked to the small port of the modulator on mine, while the large port is hooked to about a 4-inch rubber tube which hooks to a steel tube running to the top back of the engine. Where the pipe ends next to the engine, I have another 4-inch rubber tube hooked on that end which hooks to the engine. Like I said, I never knew if any of this was hooked up correctly so I left it alone. The car (and transmission) have run great in the 4 years since it was restored so I left well enough alone.