Well, I was at my watering hole last night and we got to talking about the C-6 Ford transmission I am planning n putting into my avatar car. And I mentioned I wanted to modify the shift points at wide open throttle to 5500. So, I also said the governor would have to be modified, lightening up the weights. My friend , who used to own a transmission shop, said we could do that with the vacuum modulator. When I said the VM only works at partial throttle to facilitate early up shifts for smooth shifting, and has no function at WOT, he disagreed, actually got pissed and left. Well that got me to thinking maybe I’m wrong, since my friend did own a transmission shop , some years ago. I know there has to be some C-6 gurus here….what say ye? Bones
Talk about 1st world problems. Getting mad enough to end a conversation and leave over the exact function of a vacuum modulator on a 50+ year old transmission design, seesh. That said, I have no advice for you, short of stuff the C6 in there and see what happens.
Yeah, my friend has a short fuse, he didn’t leave immediately, but he was pissed at me for not believing him! Left a tad early! We kinda get cranky in our old age! Lol Bones
We sure do. Thinking about this from a theoretical standpoint, in concept, your friend is not wrong. If you were to plot out throttle position vs. manifold vacuum, you would have two points, idle where vacuum is the highest (err, lowest) and WOT were it is the least, and some not straight line connecting those points. Similar with the vacuum modulator in a vacuum vs. position chart. When it sees a strong vacuum signal near idle, it is fully actuated and holding the line pressure control valve open so shifts happen at lower rpms. Conversely, when it sees a weak vacuum signal, the spring has the modulator closed, causing line pressure to increase and the transmission will hold each gear longer. The question, is when and were do those two curves intersect. If there is enough adjustment range in the vacuum modulator, to increase the line holding pressure to match the extra pressure created by spinning it up to 5500 rpms, your friend is correct, which gets me back to my original comment of stuff it in there and find out.
Well that’s kinda how I have it figured, I know some Modular’s are adjustable. But if you adjust the modulator to make the transmission shift an a higher rate at WOT, it’s going to shift wrong at partial throttle. I always adjusted the modulator to shift correct at partial throttle and it never seemed to change the shift points at WOT. Or at least not that I could tell! Bones
On a C6, shift points are a balance between governor pressure and throttle pressure. The vacuum modulator controls throttle pressure which also controls transmission operating pressure. Your friend (?) is right, you can delay upshifts and make them firmer by increasing throttle pressure. You probably do not want to play with a C6 governor. It is a two valve arrangement with the large valve preventing any governor pressure up to 4 or 5 mph when the little valve takes over. I had a customer with a 67 Lincoln. He was a preacher and made frequent trips between Springfield, IL and Chicago on I-55. He came in complaining of fuel mileage, but he said his Lincoln had never run better. The problem was that the vacuum line had come off the modulator and he made most of the trip in second gear. The tail pipes were snowy white, I'm sure that old 462 didn't have a spec of carbon in the combustion chambers.
To mod the governor is a cut and try process, with tailshaft housing removal each time mandatory. The '66 390 GT Fairlanes and 390 Cyclones had the correct governor weights for what you want to do, as well as all of the FE powered CJ cars, and perhaps the 429 CJ's as well. You can put an isolation valve on the modulator, and eliminate it entirely from the shifting process, which can be helpful when racing, or if you need to pedal a little doing burnouts and don't want an upshift. Finding the OEM governors can get expensive, but someone may be making them since the last time I checked, 5 or 6 years ago. I'm not sure, but I don't think the modulator in OEM form helped control the full throttle upshifts, but I think they can be adjusted enough to do so. Unless you like pulling driveshafts and housings, along with the Type F mess, you may find it much easier to do the valve body mods, shift kit if you wish, and shift it manually. Someone did post online at one time what the correct weights of the CJ or GT weights were, but that may have been in a now-dead forum. Broader may also be of help, and there could be many more out there with the knowledge.
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