I'd appreciate any help in diagnosing a problem we're having in getting the "kick down" mechanism in my '55 Powerglide to shift the transmission down into low gear at about 20 to 30 mph upon fully depressing the accelerator. We've adjusted the side linkage on the transmission that connects to the shift down rod, in an attempt to obtain full travel on the shift down side lever connected to the tranny, but to no avail. We then removed the entire side plate mechanism (the one that is connected by 8 bolts to the drivers' side of the transmission and that has the internal valves, etc., and from which protrudes the shaft to which the shift down lever is connected--sorry, don't know the proper name of this mechanism) to try to ascertain whether there was anything missing or not working inside.
We took this side plate mechanism to a local transmission mechanic who professes to work on old Powerglides. He looked at it and said that everything appeared to be working properly, that there were no missing internal pieces, and that the lever was hitting the internal "stop" properly. (He did not otherwise "test" this mechanism.) He also told us that this same mechanism is what causes the transmission fluid to shift the transmission from low to high (and vice-versa) at fairly low speed during normal operation. Therefore, according to this mechanic, if the tranny is otherwise shifting gears properly (which it appears to be doing), there is nothing wrong in the internal side plate shift mechanism, and the failure of the tranny to shift down to low gear upon stomping down on the acceleration at about 20 to 30 mph, must be due to our failure to achieve the proper adjustment in the shift down rod. We've adjusted that rod both on the lower end (at the shaft sticking out of the side plate mechanism) and at the upper end (at the intake manifold bell house), but still can't seem to get the shift down to operate when we drive the car.
Any thoughts, and two specific questions: (1) is it true that if the tranny is otherwise shifting from low to high (and vice-versa) at about 15 to 20 mph during normal operation, that the mechanism itself that should cause the "shift down" upon stomping the accelerator, is working properly and therefore our problem must be in our linkage adjustment, and (2) is it possible that we have the wrong shift down rod, which seems a little long and may or may not be original to the car? I note that we have to take all of the travel out of the carb linage to get the shift down rod to attach to the intake manifold bellhousing. Thanks very much for any help. Mike
We took this side plate mechanism to a local transmission mechanic who professes to work on old Powerglides. He looked at it and said that everything appeared to be working properly, that there were no missing internal pieces, and that the lever was hitting the internal "stop" properly. (He did not otherwise "test" this mechanism.) He also told us that this same mechanism is what causes the transmission fluid to shift the transmission from low to high (and vice-versa) at fairly low speed during normal operation. Therefore, according to this mechanic, if the tranny is otherwise shifting gears properly (which it appears to be doing), there is nothing wrong in the internal side plate shift mechanism, and the failure of the tranny to shift down to low gear upon stomping down on the acceleration at about 20 to 30 mph, must be due to our failure to achieve the proper adjustment in the shift down rod. We've adjusted that rod both on the lower end (at the shaft sticking out of the side plate mechanism) and at the upper end (at the intake manifold bell house), but still can't seem to get the shift down to operate when we drive the car.
Any thoughts, and two specific questions: (1) is it true that if the tranny is otherwise shifting from low to high (and vice-versa) at about 15 to 20 mph during normal operation, that the mechanism itself that should cause the "shift down" upon stomping the accelerator, is working properly and therefore our problem must be in our linkage adjustment, and (2) is it possible that we have the wrong shift down rod, which seems a little long and may or may not be original to the car? I note that we have to take all of the travel out of the carb linage to get the shift down rod to attach to the intake manifold bellhousing. Thanks very much for any help. Mike
you may have the throttle valve linkage out of adjustment or the rod connected from it to the swivel plate on the intake. 
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