Re: Hill Holder for BW OD Cars

Posted by Tim Cole On 2015/6/27 20:41:41

The Borg-Warner overdrive does not use gears for direct drive. It uses a sprag which locks the annulus gear to transmission speed.

Overdrive is engaged when the solenoid acts on a dog clutch that holds the sun gear stationary. With the sun gear held stationary the carrier pinions react with the sun gear to spin the annulus faster than the carrier thus allowing the sprag to free wheel.

In reverse with overdrive engaged the sprag will engage to provide direct drive at the same time the carrier pinions are trying to drive the annulus at a faster rate. Since you can't be in two ratios simultaneously the unit will lock up.

How do I know this? Once I was working on a Model 30 brass car with a BW overdrive. They had a quill shaft in place of the transmission mainshaft. When I held the dog clutch in overdrive on the bench I couldn't turn the thing backwards.

That is the operating principle of the hillbilly hill holder.

I suppose you could make a jackass video like this: Run a jumper wire to the overdrive relay bypassing the reverse lockout switch. Next get the car going 25 mph in reverse, put it in neutral, and release the accelerator. The wheels should lock up and blow the transmission.