A-500 transmission OD and LU controls.
I have seen a few good ways to control the overdrive and lock up on the A-500/42RH transmissions when swapped into older cars, and I hope I learned a bit from all of them while coming up with my own plan. So here it is. What do you think?
Forgive me for the schematic diagram, but that is the way my mind works!
Cley
View attachment 1715108691
Overcomplicated.
The governor pressure in lbs is real close to road speed in mph, so normally off adjustable pressure switches can be used to activate OD and LU.
This way there is no need for an electronic speed sensor, as the governor supplies speed sensing in psi.
NOS fuel safety cutoff switches work great for this, as they are designed to disable the NOS if there is insufficient fuel pressure. (so normally off, but contact when the pressure is high enough)
Plumbed into the governor port and set at different pressures gives you an adjustable speed range where OD and LU engage.
Then a normally on adjustable vacuum switch can be used to kickdown on heavier throttle by breaking the ground for the relay that controls the respective solenoids in the trans when intake vacuum drops below your set range.
If you build the system with power to the trans whenever the ignition is on it's easy to use ground switching for engaging disengaging OD and LU.
My own 42RH is set to go into OD at about 55mph, and LU at 70 completely automatic, but if I turn the ground off to one or the other of the control solenoids with the switches on my shifter it disables it.
If I have the OD switch on inside the car the trans automatically goes into OD at 55mph, but if the lockup switch is off then LU will not come on.
If I have the OD switch off and the LU switch on the trans will skip OD and then LU at 70mph in 3rd.
This means I can run it in 3rd with lockup, OD with lockup or OD without LU but I have never seen any real use for doing it.
Oh, and I plumbed those two pressure switches up to the back of my intake on a mounting bracket so those speed adjustments can be done from under the hood instead of under the car like some do.
