Borg Warner overdrive question

[Tosaman]

Hope this hasn't been posted before. With the B/W overdrive unit, is the governor switch always powered even if the overdrive is not being used, i.e., cable is not pushed in? If it's powered, wouldn't this mean that the solenoid also is being activated through the relay when speed exceed 28 mph? Or is there a switch that automatically cuts power to everything if the overdrive is not being engaged? Maybe a dumb question to many, but I have a B/W unit spliced into the torque tube of my '47 Ford sedan. There is no kick down switch, as power to the overdrive relay is simply from the ignition side controlled by a simple toggle switch. Just wondering if leaving that toggle on will cause any harm. Thanks.

[38 coupe]

It depends on the Borg-Warner overdrive. The first units had a switch that interrupted power when the unit is locked out. You can see this roughly between the solenoid and lock out arm on the 49-50 Ford and Mercury units. Somewhere around 1951 this was eliminated and power is applied automatically based on the governor contacts. You will have to look at your unit and see if the interrupt switch is there or not. I suspect it will not be, as most of the torque tube adaptations were made using Rambler units since they have a flange on the back that eliminates the need to weld a flange onto the cast iron overdrive housing.

[Tosaman]

Thanks for the reply. Mine OD is a bit of a "one off" installation. I think mine is an early 50's Rambler unit that had flat flanges front and back, as Ramblers back then still had enclosed drive shafts. There's no lock out switch on it, and it was only used back in the day to drop power when shifting into reverse. Along time ago I found a guy who was splicing those units in Model A torque tubes to give those cars some highway legs. I think I was the first post-war car that he did it on, as my '47 still haa a torque tube. He took a chunk out of the torque tube back towards the rear and spliced the unit in with some clever machining.


My electrical set-up is quite simple. I run a line from the ignition switch to a toggle switch and then to a small square automotive relay installed back by the unit. I use that line to power both sides of the relay with the control terminal going to the governor switch and the load terminal going to the solenoid. With that configuration, power is always on to the governor switch if I leave the toggle on regardless as to whether the OD is being used or not. That also means that the solenoid gets energized once speeds exceed 28mph, again whether or not the OD is being used (i.e., cable in or out). Looking at a standard B/W installation diagram it looks like power always is on to the governor switch and solenoid being activated even when OD is not being used.


The lock out switch that you mentioned actually has nothing to do with that and only was there is drop power to the governor switch when shifting into reverse. But as you mentioned, they dropped that switch after a while, assuming people didn't drive over 28mph in reverse!


My question remains -- is power always routed to the governor switch (and then to the solenoid) if the OD is not being used in a standard installation? Out of precaution, I turn the toggle off when not using my OD, but sometimes forget. Just wondering what kind of damage may occur.

[40cpe]

There is no power to the governor. It is a grounding switch for the relay. There is constant power to the relay when the ignition switch is on. When the relay is grounded by the governor, power is applied to the solenoid through the relay.

[rotorwrench]

The firewall relay powers the system up when the key is turned on. The system uses the governor ground to complete the circuit at the moment it reaches on speed. The downshift switch under the gas pedal is an interupter circuit that kills the ignition coil momentarily so that the main solenoid can drop out for passing. The main solenoid drops out so fast that it restores the ignition circuit momentarily. It's not easy to tell that the ignition even stopped it's so fast.

The rail interrupter switch was dropped in 1951 since it was considered to be redundant. Personally, I like having the rail switch on both of my early 51 Mercury cars. It keeps the solenoid from powering up when driving in the locked out position. These old cars only had a 35 amp electrical system so it takes bit of the electrical load off.

[Tosaman]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by 40cpe

There is no power to the governor. It is a grounding switch for the relay. There is constant power to the relay when the ignition switch is on. When the relay is grounded by the governor, power is applied to the solenoid through the relay.

I agree. However, once speed exceeds 28mph, the governor completes the control circuit though the relay and powers the relay load circuit, which activates the solenoid. My question remains that with power going to the relay, does the solenoid get activated above 28mph even though the overdrive is not mechanically engaged.

[Tosaman]

Originally Posted by rotorwrench

The rail interrupter switch was dropped in 1951 since it was considered to be redundant. Personally, I like having the rail switch on both of my early 51 Mercury cars. It keeps the solenoid from powering up when driving in the locked out position. These old cars only had a 35 amp electrical system so it takes bit of the electrical load off.

Motorwrench -- If I read your post correctly, what you call the rail interrupter is a switch that keeps current from going to the relay until the OD is actually mechanically activated. If that's correct, it's essentially what I have in my wiring. I was wondering if there was any harm and leaving that switch closed when not using the OD.

[rotorwrench]

The rail switch opens the circuit to the ground action of the governor so the main solenoid can't operate electrically. The rail also blocks the pawl so that it can't move mechanically. This is the redundancy that Ford obsoleted since it was already mechanically blocked from operation in overdrive.

If a person has an older transmission that has the switch at the back of the rail rod, they can maintain it, just disconnect it, or remove it if they wish to. It just has to be capped off to prevent leakage or muck intrusion. If the transmission never had the switch then there would be no place to install one.