The overdrive unit is a Borg Warner like is used in Ford and Mopar. When you pull the T-handle under the dash, it is locked in direct and locks out the free wheeling. When you push the handle it allows the solenoid to shift into OD. The governor in the rear of the tail shaft only allows the solenoid to shift at speeds above 28 mph. I have had Ford overdrives for 45 years. I prefer to pull the handle when I drive around town and it is like driving a regular transmission except that you have the pep and engine braking effect of 3.89 or 4.11 gears or whatever Chev uses. Also, the free wheeling at speeds of 28 mph is kind of awkward. Once I get to a cruising speed, I push in the handle, let off the gas and it shifts into OD. Ford has a kickdown switch under the gas pedal. I think Chev is in the carb. Mashing the pedal to the floor will cause it to shift back into direct.
