QuestionHi, I have a 1954 Skyliner (Ford) with a 1955 T-bird engine in it. The overdrive works but doesn't kick in until about 50mph. I'd like it to kick in sooner. Any thoughts on why it kicks in at such a high speed and how I might fix it? It has oil in the overdrive unit. Thanks in advance for your response. Jimbo
AnswerAs I pointedly emphasize in my intro on this site, I cannot answer questions about cars that have been modified, because I have no idea what has been done to it during the modification.
I can tell you how the overdrive works, and perhaps that will lead you to the answer you want: The overdrive kick-in speed is set by the governor, which is mounted in the back of the overdrive unit, the mushroom shaped object that is threaded into a hole on the side of the back of the overdrive case - it has one or two wires going to it.
It is a simple flying weight spinning device, which is driven by the worm gear on the output shaft of the overdrive. When the weights are spinning fast enough, there is an electrical switch contact inside this device which grounds a wire, and grounding that wire tells the overdrive solenoid to pull in.
Since your engine has been changed from the factory setup, it is possible that the transmission has also been changed, and even possibly the rear axle ratio - but regardless of how it happened, the output shaft is turning about 40% slower at a given speed than it should be, so the overdrive governor "thinks" it's only going 30 when it is going 50. Besides the possibility that the rear axle ratio was changed, it is also possible that someone has left the governor drive gear loose on the output shaft, so it is slipping on it's shaft, making it appear that it is going slower than the shaft. It is also possible that the wrong governor was installed, or the wrong pinion that drives the governor.
If you have access to the original parts, try the old governor first - this one may have problems.
You can remove the governor and inspect it: make sure the pinion on the governor drive shaft is tight with no slipping, and that the weights are free to swing out when you spin it, and that the electrical contacts appear OK, and that the worm drive gear in the overdrive isn't loose on the output shaft.
You say there is "oil" in the overdrive unit. Just in case, make sure it is GL4 grease (not oil), and SAE140 grade - if you are not sure, drain and refill all three gearboxes - the differential, the overdrive, and the transmission. If someone has put transmission "oil" in it, that could be the cause of your problem, as that will let the output worm drive gear slip on the output shaft. That oil is also not heavy enough for your gearboxes. Don't use GL5 85W140, use only GL4 SAE140 grease. The modern stuff is not compatible with the older gear boxes.
As a fall back position, you can always add a manual switch to short the governor wire to chassis ground when you want to use the overdrive - you can make it kick in at any speed, but be sure to use it only in high gear, and only over 25 MPH, because the gears are not strong enough to take the torque of the other transmission gears, or the low speeds.
Dick
