Extending the rod might raise line pressures a small bit, but the main issue, to me, is that they shifted too early in normal driving, which put any accel "on the converter", which would be softer and slower than if the kickdown rod has more pre-load on it. It also makes the vehicles feel "like dogs" with similar horsepower ratings of similar GM vehicles, by observation. I'm not sure of the original orientation for doing this by Chrysler, BUT in the later years of emissions rules, with emissions measured by "Grams/mile" rather than "PPM" (as originally done), the lower the rpms the lower the emissions from the tail pipe, it would seem. I have not looked, but suspect that adjustments on a C-body would be the same as a B-body vehicle with the same rear axle ratio.
In the middle 1980s, we traided for a current model year D-150 fancy Dodge pickup. Had the normal 318 4bbl V-8 and 3.21 rear axle ratio. Very similar to the same year Chevy 305 4bbl I was driving at work. So, being inquisitive, I asked the Used Car Manager for the keys to the Dodge and went out for a short drive. Right off the bat, it was doggy. If a new vehicle customer was comparing the two, the Dodge would be somewhat under-powered feeling, compared to the Chevy (with a comparable rear axle ratio). Then I tried shifting the trans manually and things changed! Getting it to a higher road speed in Low, then a bit higher than the factory shift point in "2", it felt much better and energetic. Just like I'd found in my own cars, years earlier. Same on a used Ramcharger a friend bought a few years later, too. Therefore, I suspected the early upshift orientation was something burried deep in Chrysler engineering rather than really what made the vehicles feel/drive better. Which might also related to their late-adoption of part-throttle downshifts, too?
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In earlier times, it was the mark of a luxury car that once you got the manual trans out of low gear, you could shift directly into "high gear" and drive the car all over town without shifting, except for stop signs and red lights. This was "luxury". Not unlike the 1970 and prior TFs which went into high gear and didn't come out until road speed dropped enough for a downshift or WOT happened. In the mean time, possibly millions of potential buyers came to drive "the new, hot-performing Chrysler products" and were disappointed in how they ran? Just knowing that the similar Ford or GM products "ran better". Not paying attention to the fact that the Chryslers usually had sharper throttle response due to the design of the TF torque converter. All these potential customers paid attention to was what happened, and kept happening, when they punched the throttle, by observation. Early upshifts didn't help the vehicles parform as they could.
In a lighter B-body, with possibly a different trans governor, things worked pretty well. So . . . . take the time to shave the trans governor weights (2bbl and 4bbl governors were different, as I recall, usually, especially on the 4bbl HP models) or put a bit more preload on the kickdown rod (like 2 more turns preload on the threaded rod or the .10" wide wire tie on the rest, at the bottom back of the slot in the rod) as I did.
The quicker/firmer shifts of the TF has always been liked and felt/heard, but when they happen too soon, the result is really noticed more than on a Ford or GM trans.
Just my observations,
CBODY67