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Could someone please explain how the kick down circuit works? It looks like the kick down switch on the throttle grounds the ignition coil which should kill the ignition altogether.
So by eliminating the ignition, how does this facilitate the drop down from overdrive to the normal drive ratio?
This is done so that you can change from overdrive to a lower gear ratio to allow for higher RPMs for passing or accelerating up hills.

I don't see how grounding out the ignition coil and eliminating the distributor gets the car to downshift out of overdrive.

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You are correct in that the kickdown action could kill the engine but due to a sequence of operation and close timing between various contacts the ign is only shorted a very brief time.

When the OD completely engages the solenoid plunger extends the pawl into the sun gear and by that action the cutout contacts inside the solenoid close. Ground is then present at one of the terminals on the kickdown switch but that set of contacts in the switch is open so ground goes no farther.

When kickdown is desired and the accelerator is pushed all the way to the floor the kickdown switch does two things. When the plunger in the switch starts to move the first set of contacts near the plunger open to drop out the relay and by that action, the solenoid loses power. With the continued movement of the accelerator and plunger, a brief moment after the relay and solenoid lose power the second set of contacts in the kickdown switch close and the ground passes thru the kickdown switch to the coil terminal and shorts out the distributor pulses.

When the ignition quits, almost instantly the engine loses power. By losing engine power the torque or pressure the sun gear is exerting on the pawl is relaxed and with the solenoid off, the spring inside the solenoid can retract the plunger and pawl. As soon as the plunger moves back into the solenoid the closed cutout contacts open and ground is removed from the kickdown switch and ultimately the coil so engine starts to run again. You are also out of OD because the pawl is no longer holding the sun gear. The entire sequence only takes a few milliseconds to complete so the engine never has a chance to stop rotating and die before the spark is established again.

If there is a mechanical problem and the solenoid takes too long to retract, conceivably the ign would be shorted long enough for the engine to die. As a second protection, if the engine starts to die instinct would have the operator working the accelerator. As soon as the accelerator is relaxed and moves away from the floor the cutout contacts in the kickdown switch would open also removing the ground to the coil and the engine would stay running.

In the kickdown sequence, once the reason for kickdown is over such as needing more power when passing a car, if the car is still moving above the governor cut in speed the OD will also be ready to re-engage when the accelerator is released. If OD is not desired again it will be necessary to lock OD out via the knob on the dash.

Here's a short video someone made showing how his overdrive works.

youtube.com/watch?v=hVFiRkkvask

Wes

I had something go wrong with the kick down system on my 1952 Henney-Packard that maintained the coil's short so on the highway when I floored it a bit too long to pass someone, when I released the gas pedal and the coil reactivated, I blew out the seam on the nearly-new muffler from end to end when all the fuel still going into the cylinders ignited! Point is to be careful when testing that it actually is releasing momentarily.

Good explanation! Thank you!

So what would make the car miss and run poorly AFTER kickdown?
That's what mine is now doing . Ne relay, solenoid, kickdown switch. Runs fine when in overdrive, but when you mash the accel all the way to the floor, runs terribly. Also, it won't come out of overdrive at 23 mph, only when stops. Bad governor?

Am reasonably sure the kickdown circuit is not the issue because if that were acting up in all probability the engine would die completely when it kicked down since the short to the coil would not go away fast enough to prevent killing the engine.

Engine guys would be better to diagnose the poor running issue but two things happen when it kicks out of OD. One is with the accelerator down, throttle is wide open so there is a large change in the fuel-air ratio. Possibly it is the carb that is acting up. The other is with the throttle open there is suddenly reduced vacuum available to the distributor advance so that will move. Not knowing what dist you have there could be grounding issues if the advance is the type where the whole distributor rotates or a faulty wire on the inside could be causing problems if the type where only the inner plate rotates. If the problem is in that area, obviously neither has got to the point where there is a complete lack of ground or a shorted wire or else the engine would die. A bad capacitor could also be causing problems.

The governor should be releasing the contacts to drop the relay and solenoid out as it slows down below the cut in speed. I think there is around a 4-5mph band where the transition can occur. Possibly someone has messed with the adjustment but since it apparently comes in on time that would be less likely than possibly the flyweights have become gummed with oil or grease and are not free enough to be able to drop quickly as they slow down. If that is the case the switching mechanism might not be triggered until the car is stopped and there is no more inertia. Without any movement the flyweights can slowly drop and let the switch open.

Thanks. Just had the carb rebuilt. Its got the turning plate inside. Will check out both!

Without putting the car in overdrive, take it up to 25-30 MPH and then step on it to the floor, all the way to the point where you can feel the resistance of the kick-down switch (even though the switch is off). If you're not familiar with how that feels, you can press the pedal in the garage without the engine running until you feel that little bump.

If the car doesn't smoothly run up to 50 MPH with the pedal full throttle, the problem is not the overdrive. If it knock and pings the timing could be too advanced, fuel octane is too low, like that.

If it runs rough, as Howard detailed, the distributor and the carburetor could have issues.

I personally don't like pulling the overdrive cable out unless I'm practically to a stop. When traffic hits a congested area, I'll wait until the car in front is almost stopped and then I'll put in the clutch and pull out the OD.

Since we're discussing overdrive. When you press the gas pedal clear down and engage the cutout switch, this momentarily grounds the ignition an the overdrive disengages.
So does the overdrive re-engage when you let the gas pedal up some or does it stay disengaged till??


John