Editing General Motors transmissions (section)
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==3-speed manual overdrive units== ===How overdrive works=== The governor powers the solenoid in the mid 20's MPH, you have to let up on the gas pedal to let it shift up. When you push the pedal to the floor the kickdown switch cuts off the power to the solenoid and temporarily cuts off power to the ignition coil so the engine stops running for a second or two. This lets the spring on the solenoid retract and shifts out of overdrive. When you drive less than the governor speed setting in overdrive it cuts off power to the solenoid. If you are going up a hill and the car does not coast the solenoid will not retract and you will still be locked in overdrive. When you are in overdrive you can not go backwards. This was called the "hill hold" feature. The pull out T-handle is used to lock up the trans into regular 3-speed mode. This is useful when pulling a trailer uphill and important when going down hill. If the handle is pushed in you can coast and not have any engine braking. When you were cruising and in overdrive second gear and some one pulled along side and wanted to race you could stick your toe under the gas pedal and push down on the kick down switch to gear down before hitting the gas and opening all three carbs. When you wire in a toggle switch to operate the relay to power the solenoid you could shift it into overdrive in any gear and not have to be above the governor speed in first gear. Just like driving a big truck with a two speed rear end. Just remember you have to let up on the gas to let it shift up into overdrive and when you turn off the switch you also have to let up on the gas to let the spring retract the solenoid to shift out of overdrive. If you leave the switch on and are in overdrive you can not shift into reverse and you cannot roll backwards. ===Borg Warner OD wiring diagram=== [[File:Od-wiringdiagrm.jpg]] <br style="clear:both"/>
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