[tjs72lemans]

I replaced my tranny kickdown solenoid, since it went bad. Now it works. But, Is that the only time the tranny shifts to a lower gear, when the pedal is floored? I thought there was a governor or something that automatically shifted down at slower speeds and speeding up. If you were doing 30 and pushed accelerator down, but not floored, it would kick down from 3 to 2nd? The tranny has been rebuilt and it only kicks down a gear when floored.

[Cliff R]

The solenoid is only for heavy/full throttle down shifts. On the TH400 the transmission will select the appropriate gear based on vehicle speed when the solenoid is activated. So at lower vehicle speeds when you go to WOT it usually goes to low gear, at higher speeds to 2nd gear.

At light throttle or "normal" driving it will select the correct gear based on engine vacuum to the modulator combined with vehicle speed (governor). You may or may not get a shift to a lower gear once you reach high gear if the vehicle is traveling at higher speeds. Most modulators are adjustable within a limited range so you have some control of light or part throttle upshifts/downshifts.......

[Half-Inch Stud]

^^^^^ Yez. The kickdown reveals the TH400 STREET virtues over the Manual 4-Speed combos.

TH400 TRACK virtues are clearly superior to all Factory Manual transmission offiering.

[kingbuzzo]

This is interesting since I'm experiencing the same issue.

I didn't know there was a kick-down solenoid.

Thanks!

[Formulajones]

The solenoid is on the side of the trans near the shift linkage. Usually an orange wire running to it.

If no kick down I'd first turn the key on and manually apply the switch at the gas pedal (or carb depending on model) and see if you hear a click.

It could be as simple as adjusting the switch. Sometimes they get out of adjustment with an over zealous foot stomp on the loud pedal or maybe a floor mat has moved. They are pretty easy to adjust a reset.

The vacuum modulator will play a small roll in the part throttle stuff. As Cliff touched on, most of them are adjustable. Remove the vacuum line and inside the nipple is a small screw.

If you find the car going through the gears quickly and shifting prematurely at part throttle, turn the screw clockwise, tightening the spring, will increase part throttle shifts. This will also increase part throttle or light throttle downshifts to some degree.

For instance, if you slow to turn at 15 mph, then go to accelerate and find the trans is still in 3rd gear and you feel it would be better if it rolled away in 2nd gear, then turning in the vacuum modulator screw will help this scenario. This will consequently also hold 2nd gear longer at part throttle as well before shifting to 3rd. I usually find this tweaking necessary on cars that have long rear gears so the engine doesn't have to lug in 3rd at those slow speeds.

[ta6point6]

Well my experience is in my truck and it has a th400. I was having trouble like you did not shifting down a gear. I started with changing the vacuum modulator and that made a big difference in 3rd shifting down to 2nd even at partial throttle. I have not messed with the switch by the gas pedal in truck yet. When I have time I am planning to replace switch and adjust at the gas pedal. Changing of the vacuum modulator made such a big difference in how the truck runs I am in no hurry to look into the switch though. The vacuum modulator is less then 30 from Rockauto so fairly inexpensive just to replace a 40 year old part.
Good Luck

[tjs72lemans]

Thanks for some of the input on the function of downshifting. Once again, this tranny was rebuilt and new vacuum modulator installed during that time. After motor and tranny rebuild, the tranny only kicked down when floored one time. It never downshifted at slow speeds and accelerating or going up a steep hill. I did troubleshoot to the point of finding my kick down solenoid failed. With that replaced and now having a downshift at wide open is positive. Now I'm onto figuring out why it doesn't shift down during slow speeds. I also don't notice downshifts as I slow down (no acceleration). I may have to mess with that modulator spring and see what happens. The tranny shifts from 1st to second at about 10mph and to 3rd at about 25-30mph with slow acceleration. Does that sound about normal?
Also, I have one small drip at speedo cable connection. Is there an o-ring there that may be bad? Or why would that drip?

[Formulajones]

Light throttle shifts of 10 mph and 25-30 mph sounds pretty normal.

Yes the speedo housing has an o-ring that seals it.

[tjs72lemans]

Thanks for that info.