Vacuum Hose off C4

[Viperwolf1]

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.

Like I said earlier, either block the side port and just use the rear or swap it for a single port. It wasn't designed to use full vacuum at both ports so it's hard to tell how it would act.

 

[Viperwolf1]

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

I think I got it here: http://www.mustangbarn.com/vacuum.html

 

[Broncobowsher]

For now you should be able to run with the rear port to manifold vacuum and leave the front open. Don't cap it or pressure can build up from heat or the movement of the main diaphragm. That should act like driving without the EGR active.

The EGR adds a little extra pull to the modulator. When the EGR opens the engine has less vacuum but not extra torque. That loss of vacuum at cruise would normally make the transmission go into a later, firmer shift. So to keep the transmission shifting correctly with the EGR open a larger, secondary, diaphragm is used to help the main one. A booster to the modulator for when running the EGR.

If you were to Y the 2 ports you would have very early and soft shifts. The transmission would be adjusting for very low torque inputs even under moderate loads. There is a good chance you could get the transmission to start slipping and burn it up. Bad idea. The single port is a pretty foolproof way of going conventional. If you are stuck running around with that dual port, let that front, large diaphragm breath freely and just use the standard port.

 

[BRONCOBERT]

When you pull the modulator out will transmission fluid flow out from the port it was in and if so should the fluid be drained first before swapping one out?

 

[Justafordguy]

You will lose some fluid but not much.Just be ready to stick the new one back in quickly. I always park with the nose down hill to make it leak less. Also be aware of the little pin that will sometimes come out with the modulator. It must go back in so don't loose it.

 

[DJs74]

The modulator will have a piston style oring seal - make sure you put a little fluid or something on it to serve as lubrication just before you install it --- and, push the modulator straight and smooth into the port. If you push it in cantered, you take a chance on nicking the oring.

As mentioned, watch out for the pin inside the modulator valve.


DJs74

 

[BRONCOBERT]

The one I am looking at has the adjuster on it. Should I adjust it before installing?
Just wondering proper way to adjust, should I start off with factory setting or put it in the center and start from there?

 

[Broncobowsher]

Put the new modulator in as is for now. Starts you with a baseline.

 

[lowbush]

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

They also make an adjustable one that is worth the few extra dollars but I don't think you wont find it at the local parts depot, it's a order and ship type product.


EDIT just saw that you posted that you have an adjustable one, put it in stock which will be the same as the green stripe setting (IIRC), then if it is not shifting how you want it, try adjusting it a little and then test again.

 

[BRONCOBERT]

The adjustable one I posted has the green stripe.
So you guys figure that they are adjusted from the factory and not just randomly different from one to the other.

 

[74strokerbronco]

yes there preset in the middle of there range you can adjust cw for later firmer shifts up to 2 -2.5 turns or ccw for softer earlier shifts up to 2- 2.5 turns . some will go 3 turns either way but that's it . mark your final adjustment on it with a permanent marker for future reference is always a good idea too such as +1 cw.

 

[BRONCOBERT]

Ok, got it installed and it has a little bit of wiggle room back and forth, is this normal or should I take the bracket of and bend it a little to make it snug.

 

[BRONCOBERT]

Also wondering if I run this off manifold vacuum and have distributor vacuum advance also, can I tee of the same vacuum port on the front of the carb?

 

[Viperwolf1]

Also wondering if I run this off manifold vacuum and have distributor vacuum advance also, can I tee of the same vacuum port on the front of the carb?

Run the C4 off manifold vacuum. Distributor is usually ported vacuum.

 

[BRONCOBERT]

By wiggle room I mean with the bracket snugged down, I can still move the modulator in and out a small amount. Is this something I should correct?

 

[BRONCOBERT]

Can I hook up the modulator to a port on the back of the manifold? they are all caped off but I could buy the 90 degree NPT, I assume it would be the port on the tallest runner?

 

[Viperwolf1]

Yes, any vacuum port back there will work.

A little wiggle at the modulator is ok.

 

[BRONCOBERT]

Thanks Viperwolf, I was worried that a little wiggle room might affect is performance.