The Stovebolt Site Forums The Shop Area Driveline Overdrive Now Fully Functional!

My 3-speed with overdrive now operates as God intended! There are already several threads regarding how to wire overdrive. However, I thought I would share what I've just learned, to hopefully aid others who want the automatic overdrive functionality. I may break this into several smaller posts, for readability and clarity.

I bought my '61 Apache last year...my wife and daughters call it " 'Mater Jr.".

It has a Jasper crate engine with an aftermarket Carter YF carb. It appears that when the engine swap occurred, the original bracket and kickdown switch would not fit the new carb, so the owner never bothered to reconnect the overdrive. The gentleman I bought the truck from had installed an overdrive relay, but no kickdown switch.

Since an original switch wouldn't fit anyway, I made a bracket and switch by using two SPDT micro-switches. I mounted this to the Carter YF, so that at full-throttle, the switches are engaged by the throttle linkage. I went with a carb-mounted switch rather than an under-the-pedal switch because: a) carb-mounted is most like the original, b) I didn't want to drill a hole through the floorboard, and c) I didn't want the switch where a floor-mat or other object could get caught and possibly interfere with operation.

I did my homework; there are numerous wiring diagrams on the web, but some of them are unclear, misleading, or downright wrong. One pole of the switch is normally-closed, which allows power to the overdrive relay. The other pole is normally-open, which is connected between the overdrive solenoid and the negative side of the ignition coil. At full throttle, the switch engages...one pole removes power from the overdrive relay, and the other pole grounds the ignition coil through the overdrive soleoid, which momentarily impedes the spark and creates a 'torque pause', allowing the overdrive to mechanically disengage. When the overdrive solenoid is disengaged, the path to ground is broken internally, and ignition coil function is restored. This whole process is very quick, and feels just like kicking into 'passing gear' on an automatic transmission.

On the test drive, when I tried to engage the kickdown function, the ignition would lose spark as long as I had the pedal pressed...the solenoid would never break the ground circuit. The full-throttle loss of spark would occur even when overdrive was not engaged, which shouldn't happen at all. I immediately suspected that the solenoid was internally grounded.