How can I make the c4 in my 73 shift slighty later than what it is doing now? Right now, unless I am really on the throttle, it is in 3rd by about 20 miles an hour. It kicks down correctly and if I am really into it it won't hit 3rd untill 60(speedo, more like 70-72).

Also, there are two steel vac lines that run down the firewall to the tranny, only one of them is hooked up and if I unhook that it won't come out of first. Should the other one be hooked to vacuum(if so carbed or manifold)?


Thanks guys!

 

on pass side of trans is the modulater that is where the vacuum line should go up and hook to manifold for vacuum if you unhook that it will not shift to second. they selll an adjustible modulater to move your shift points by turning the modulater in or out to adjust your shifts.I don't know what other line would be.

 

Does the truck have EGR (I know, it sounds unrelated)?

 

Yeah the truck was\is an egr truck. The valve is long since stuck and a new one was something like 90$ so I said forget that.

One interesting thing is if I put the shifter in 2nd it actually shifts into second, even if your at a standstill. I have never had an auto that would shift like that.

So I just need to go get an adjustable modulator to make it shift later. Cool.

Thanks guys.

 

As far as what the two lines going down to the transmission are for - on some early-model EGR motors, there was originally concern that vacuum would drop when the EGR valve opened, which would change when the transmission shifts. That's why a second ported vacuum line was run to the modulator, in addition to the original manifold vacuum line, to increase the amount of vacuum running to the valve when manifold vacuum drops slightly. However, this wasn't around very long, because vacuum doesn't really drop after all when the EGR valve opens. This is why you see two vacuum lines running to the transmission modulator on some models. You can trace the lines to be absolutely sure. But if your question was originally what connects to what, all you truly need is one line from the modulator, to manifold vacuum. You can pull manifold vacuum off a vacuum tree on the intake. Don't worry about a second ported vacuum line - as I was saying, all this was was an early attempt at fixing EGR driveability issues and is not necessary. Just make sure there isn't a "T" somewhere near the modulator that the second line splices into, because if it's still there, you could have a vacuum leak. You need a sealed, unbreached line running from the manifold vacuum source all the way to the modulator.

 

Gotcha, thats exactly what I'm running at this point, so I guess I'm good to go. I do appreciate your clearing the whole second line thing, thanks!

Any idea why it goes into second when I put it in second? Or is that just the way c4s are?

 

mostly all Ford trans do this it was there dual range if i thinking right it started in 65 it helps in winter driving to start in a higher gear.