This is a circa 1950 (1949 models are mentioned in the electrical text) official Borg-Warner Overdrive Instruction Manual. It covers how the R-10 and R-11 units operate as well as troubleshooting and repairs. The electrical section covers the most often used wiring in 1949 models. Note that the wiring schemes changed over the years, mostly for simplification. Mid 50s and later models don’t use the “shift rail lock-out switch”. This was due to a change in the OD unit design, which replaced the electric switch with a mechanical reverse lock-out. Consult the TSM or wiring diagrams found on this site for exact wiring.
Technically, you only need a power source to the shift solenoid to operate the OD unit. “Straight wiring” the unit with a toggle switch to the solenoid can be dangerous to the unit though! When wired this way you MUST use the clutch when disengaging OD. The planetary gear shafts will not take the stress of dropping out of OD with the engine applying ANY torque or braking. To engage OD just flip the switch on and let off the gas pedal. It will engage at any speed and in any gear since the governor is not used. To disengage PUSH IN THE CLUTCH then turn the switch off, then left the clutch out. If you simply let off the gas and turn the switch off it will disengage… for a few times. At some point one of the planetary gear shafts will break, causing the gear to jam inside the output shaft ring gear (some call it a “drum gear”). This ruins the splines inside the ring gear, and of course the planetary gear assembly will require replacing as well. At least you won’t be stranded, as the OD unit just jams. This takes out the free-wheeling as well, leaving you with a straight three speed. You will know when this happens, as there will be a loud “bang” under the floor as the hard shaft breaks and the gears jam. I found this out many years ago the hard way! A switch to the solenoid is a good way to test OD operation, but unless you’re the only person that will be driving the car it’s NOT recommended!
The kick-down switch momentarily grounds out the coil, which kills the engine for a split second, taking all torque off the OD unit as it disengages. When I used an OD unit behind a fuel injected engine I wasn’t sure how the electronic ignition module would react to grounding out the coil — it would probably burn it up. I used a relay to cut power to the ignition module instead, which still killed the engine momentarily. The kick-down switch tripped power to the relay momentarily instead of grounding the coil.
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