Vacuum Hose off C4

[doradoguy]

I have two vacuum hose that attach to the back of the C4. I did an EFI engine swap and not sure where to connect them. I'm assuming they are vacuum.

 

[Stephen]

are you sure they arent the feed and return from the trans cooler? never heard of vac lines on a trans before?

 

[Explorer]

are you sure they arent the feed and return from the trans cooler? never heard of vac lines on a trans before?

They go to the vacuum modulator for shifting. Some had one, some had two. I've personally only ran into the single hose and it connects to manifold vacuum. Viperwolf is the tranny expert on here.

 

[Stephen]

good to know, i havent messed around with autos before. i like rowing my own gears, thanks tho

 

[Viperwolf1]

The 2 port modulators were used in '73-'74 in conjunction with the EGR system. Best method to get rid of it is to eliminate one of the lines and swap the modulator to a single port, green stripe one. It needs full manifold vacuum.

 

[doradoguy]

You guys are awesome. Where might I find a single port. Is that a junk yard item.

 

[dmwelljr]

You can get them on eBay, or the parts store, they are fairly inexpensive. I have one with a yellow stripe, what's the difference between the yellow and green?

 

[Razorbackbronco]

Speaking of modulators, I just had my tranny rebuilt and the modulator keeps popping out a little. It only comes out about a 1/4 inch, but it when it does it drips fluid. Is the modulator under pressure? It seems like it pops out due to air pressure, because I haven't driven it yet

 

[dmwelljr]

There should be a lil bracket that bolts in to keep it from popping out

 

[dmwelljr]

I'd post a pic, if I could figure out how!!! Lol

 

[Viperwolf1]

I have one with a yellow stripe, what's the difference between the yellow and green?

Yellow stripe, with one single hose connection for High Vac lower altitude driving. Usually found on larger engines with strong vacuum signals, and trucks with earlier governor shift point calibration. Usually found on 72-81

Green stripe, with one single hose connection for average settings that fit the widest variety of applications of the C-4 and C-5. This version seems to be the most popular and widely used of them all. Usually found on 72-83

 

[Viperwolf1]

There should be a lil bracket that bolts in to keep it from popping out

Yes. Looks like this.

 

[BronCowie]

... and this

 

[doradoguy]

I ordered my green stripe but it doesn't come with barb end. I guess I can figure that out.

 

[Razorbackbronco]

Yes that's what I'm missing! Thanks! Where's a good place to get one?

 

[BronCowie]

Yes that's what I'm missing! Thanks! Where's a good place to get one?

They are hard to find in my area; looked in all the parts houses, ford dealerships, finally found one in a small local tranny shop. The owner had one in a box up in the attic. Good luck.

 

[BRONCOBERT]

Could you not use a Y to connect the two hoses into one and run that to your single vacuum port?

 

[Viperwolf1]

Could you not use a Y to connect the two hoses into one and run that to your single vacuum port?

Not really. The vacuum sources were not the same.

 

[dmwelljr]

Not really. The vacuum sources were not the same.

Where did you find that vaccum diagram? That looks helpful.

 

[BRONCOBERT]

Not really. The vacuum sources were not the same.

What should you do if you have the C4 modulator with dual ports but don't have all the other valves?
Should I block one port and use the other, or change the C4 modulator to a single port?
Also what negative reaction would happen if you ran the Y for both of them.