The trans won't kickdown. The switch is good because there's power at the solenoid end when the accelerator is floored. Is there any way to test the solenoid without replacing it? And how big a job is replacing it? Are there any other possibilities why it's not working? I'm sure the vacuum modulator needs adjusting, because at partial throttle it shifts 1-2 at about 10 mph and 2-3 by 15 mph. Could this be affecting the downshift? Thanks very much for any insights.
If you are getting 12 volts at the transmission end, you should be able to hear the solenoid click. Just turn the ignition on, and operate the gas pedal switch, and listen for the click. It helps to have a quiet garage. Alternately, you can use a jumper wire from the positive battery post, and just touch the transmission connection. If you cannot hear a click, it can also be the wiring inside the pan. In any case, the solenoid is easy to replace (2 bolts), and accessible, but you have to drop the pan.
If the detent solenoid is bad, try a local transmission shop for a used one in good condition first. Devon
http://www.ebay.com/itm/GM-TH400-DETENT-SOLENOID-TRANSMISSION-PARTS-NEW-34420-/200281063964 http://www.transmissionpartsusa.com/TH400_TH425_Transmission_detent_solenoid_p/460-000046387.htm
