Hi engineer:
"If your throttle position switch is disconnected, how does the 3-position solenoid know that you have taken your foot off the gas pedal? Normally, the closing of that switch makes the transmission shift up."
I think something is amiss with the wiring, that puts the 3-position switch in the second position at all times, not just when the car is put in gear. So it does not need the switch anymore for that actuation.
"Is it now just the vacuum that makes it shift? At one time, I recall, you thought that the microswitch at the firewall was part of the transmission control. But that switch, I discovered, engages the fuel shut-off solenoid on my injection pump. The switch on the outboard side of the throttle plate is the one which signals to the transmission that the throttle is closed."
I have no microswitch at the throttle plate, AND I also do not have a fuel cutoff solenoid on the FI pump. So the switch, when it was hooked up (until a garagist unhooked it years ago), did in fact control the 3-position solenoid
"You also said that your transmission shifts very smooth from 2 to 3. Mine shifts smooth most of the time-after adjustments, but sometimes it is still harsh. (Only the 2-3 shift is harsh). I am comparing it to my Toyota."
Yes the trans shifts smoothly 4 out of every 5 shifts I would say. But that seems to have more to do with vacuum settings (and maybe a properly functioning 3-position switch).
"You also said, that your transmission shifts down under increasing load, like modern transmissions do (because of decreasing vacuum). Mine does not do that: I have to use "kick down" or use the shift lever. If your transmission shifts fine, and the 3-position solenoid is not working, maybe we should disconnect it?"
I am 75% sure that my car used to downshift when I applied more throttle but before pressing it all the way to actuate the kick-down switch. However, Joe Alexander posted yesterday that our transmissions are not supposed to do that. And someone else reported that their car downshifts when more throttle is applied. At this point, I think I will only find out on my car through a lot of fiddling with wiring and settings.
Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic