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I’ve got a ‘73 454 with a TH400 transmission. I’ve been having some issues with the transmission not downshifting at WOT. I’ve had the car for about two months now, and the issue just started about a week ago after I changed the coolant. I read some threads on here and I suspect the issue either lies in the kickdown switch or solenoid. How can I test this?
I got underneath the dash and found the kickdown switch (holy hell - how do folks get in there!?). I turned the ignition on and pressed the detent down and I didn’t hear a click in the transmission. I assume that I can test power with the voltmeter but I’m not sure which wires I should be testing?
Any guidance would be greatly appreciated! Thanks in advance.
Yes...use a voltmeter to determine if 12vdc is getting to the kd switch, then is being passed to the trans when the switch is 'made'. If voltage is getting to the k/d connector on the side of the trans, then your issue is the solenoid dump switch mounted to the underside of the trans valve body. It could have the orifice plugged so that it will not release or it could have just failed.
With engine OFF, if you supply 12vdc to the k/d connector wire (and ground to the trans case), you SHOULD hear that solenoid switch when it activates. If you do not hear it, that is likely the issue.
P.S. If that solenoid switch is your problem, find and purchase a replacement BEFORE you open the trans sump. You can still drive the car SAFELY now. If you drop the pan AND have the replacement part in hand, it is a quick repair. If you don't have the part, the car will be down....until you DO have it.
TH400 Kickdown Switch Troubleshooting
