Re: Need a photo of a 51-54 overdrive kick down switch

Posted by HH56 On 2015/9/1 22:52:21

I don't have any decent photos of the 51-4 switch. Not sure what you need in the way of troubleshooting photos. It is a 4 terminal two independent circuit switch. Set of contacts near the plunger are normally closed and the two others on the opposite end are normally open.

The bottom two terminals next to the plunger being normally closed are used to open the relay coil ground when kickdown is desired. As the accelerator hits the plunger and it starts to move upward the bottom two terminals are opened to kill the relay. As soon as the bottom two relay contacts open, a slight movement more of the plunger connects the top two terminals together which is one of two sets of contacts in the ign cutout circuit. Those contacts then connect ground originating at the solenoid to the ign coil for the cutout.

The relay having dropped out also drops out the solenoid. As soon as the solenoid loses power and the engine misses due to the cutout, engine torque is relaxed so the spring can retract the plunger. A slight distance back into its case and the plunger opens the second set of contacts in the cutout circuit to remove the ground to ign coil so the engine doesn't die. The whole operation shouldn't take more than a few milliseconds.