How does a trans brake works?

Answer 1

"Some automatic transmissions modified or designed specifically for drag racing may also incorporate a transmission brake, or "trans-brake," as part of a manual valve body. Activated by electrical solenoid control, a trans-brake simultaneously engages the first and reverse gears, locking the transmission and preventing the input shaft from turning. This allows the driver of the car to raise the engine RPM against the resistance of the torque converter, then launch the car by simply releasing the trans-brake switch."

"In drag racing, a transbrake is a mechanism that selectively places the transmission in first and reverse gears simultaneously, effectively holding the race car stationary as if the foot brake was applied. The transbrake is activated by the driver by applying electrical current to a solenoid at the transmission. With the transbrake engaged (transmission locked), the engine throttle can be increased to any position (opening) in preparation for launch without the race driver worrying about the car creeping forward. Milliseconds before the green light illuminates on the Tree the transbrake is released (by the driver releasing an electrical switch or by a delay box "timing out" originally triggered by the driver releasing an electrical switch) and the car launches forward, its engine already in the higher power band and the transmission already in low gear. It was invented by Billy Whatley in the year 1973."