Working on a 34 Ford with flathead, and 1963 Ford automatic. The transmission has 11 bolt pan, but has a C3 year for casting number, being 1963. My question is this: It shifts early 5-8 mph to second, 20 mph for 3rd. We thought it might be the modulator valve adjustment. We have adjusted the screw in 5 turns from where it was on the modulator with no change. Of course we have no idea if it was in the right spot to begin with. So we removed the vacuum from the modulator to see if we were thinking right, thinking it would shift a lot later and hard, but the results were the same, early shifts. Any suggestions? The cable for kickdowns is not hooked up, thinking this is just for kickdowns. Any suggestions or corrections to our thinking?
C3 should have thirteen bolts on the pan with a small bump out on the passenger side. Used from 74 to 86. Sounds like the problem many have with C4's.
I had a C4 that did that too. I found after three modulators, the pin behind the modulator comes in several lengths. It has been so many years I dont remember if I went longer or shorter.
I believe the adjustable modulators are made to allow use of any pin. Screw in to make shifts earlier. No more than 4 turns if I remember correctly. The change is slight anyway. I have this problem with the C4 behind a 302 in my 46. This happened not long after having it rebuilt, and the guy moved out of state. So, I have lived with it. I have changed modulators and checked to insure vacum to the modulator. Any time I want performance I shift it manually and it works great. I have been told it could be a sticking govenor, or possibly a torn gasket between upper and lower valve bodies. One of these days I will pull it and see.
thanks for all your input and help. the car does run fine if shifted manually. what has me confused is, i was told that a lack of vaccuum or a defective modulator would cause the shifts to be higher in rpm and harder, but i unhooked the vaccuum completely and it still shifts the same. ??? thanks, mike
Look, regardless of what type of box it is, is it safe to assume the cable is only for kickdowns?? Why not pull the cable all the way out to see how far it pulls, and see if there is a detent feel to it, that is, does it have a resistance near the end which you can overcome if you pull harder.. If it do or if it don't why not pull it about 3/4 the way out and see if it makes the shifts later and firmer?? I'd be trying that first. Obviously the next step depends on what happens when you try it. Mart.
Where do you have the vacuum hooked up on the carb? I had a C4 transmission once that had vacuum hooked to the wrong vacuum port on the carb and didn't shift correctly.
Try what Mart said. The "kickdown" affects line pressure, which affects shift points.If you disconnect vacuum to the modulator, it will stay in first gear. Since yours still shifts, you have other problems. The tailshaft housing should come off the trans while still in the car. If Mart's suggestion does not change things pull the housing and inspect the governor. Once you get the shift points to change, you can "tune" it. You can change the pin length in the modulator by putting a shim between the modulator and trans case.
once again, thanks so much for all your help. to be a little clearer on the casting numbers, according to the chart, this tranny was made in 63, probably for an early 64 mustang, but it has a hold down clamp to keep the modulator valve in place and i was told that early c-4s had screw-in modulators....so we might have a bunch of parts from various years. ?? i will try all of the suggestions and see what happens. mike
This casting number was part of the main body casting, on the passenger's side. Here is a link for decoding, hope it is of some assistance: http://mustangtek.com/FordDecode.html
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