My th400 was shifting fine on thursday night at 4600 rpm and now when i get in it, i will see a 4000 shift and then it will not down shift when i hit the gas. thank you in advance
Check continuity on the 12v wire from the kickdown switch on the gas pedal to the transmission? Or the ground. Also check to see that the switch is closing when you floor the pedal. Believe it or not there's an AM radio frequency you can tune your radio to that will put out a click when the kickdown solenoid activates. I'd have to look in the Sessions book to find it though.
You can turn the AM radio to 1400 between stations. Engine off, ignition in run position. Push the gas pedal switch, and listen for a pop in the speaker. You won't hear it, because your problem is the downshift system isn't working. That's why the trans is short shifting. Very simple to troubleshoot. The gas pedal switch passes 12 volts down to the side of the trans. The downshift solenoid energizes and opens, and the trans downshifts. Run a jumper wire from the + post of the battery, and touch it to the vertical connector on the drivers side of the trans. Listen for the solenoid click. If it does, you know the solenoid OK. If not, drop the pan, and check the wiring and solenoid(It's easy to replace, 2 bolts and wiring connections). If the solenoid is Ok, your problem is the gas pedal switch, and/or wiring. Check those out with a multi-meter.
