Delay Box - Mechanism

Mechanism

The delay box acts as an on-board timer for the transmission brake (commonly referred to as a "trans-brake"). A transbrake is a part of a racing automatic transmission used in drag racing, and are not found in manual transmissions. The electronic timer is packaged in a metal enclosure when sold to drag racers, thus the slang term delay box. This timer box is a very accurate type of monostable multivibrator (electrical engineers also call this type of multivibrator a "one shot"). The timer box acts like a time-delay relay. Many delay boxes actually have an internal relay to switch output current, but some models have solid state transistorized output circuits. The transistorized type made today almost always use power MOSFET type output circuitry. Drag racing delay boxes are designed to operate from the vehicles 12 volt DC electrical system. Some drag race cars now use 16 volt DC systems, in such a scenario the delay box has to be capable of working properly from 16 volts DC, as well as 12 volts DC.

The race car driver holds an electrical pushbutton switch depressed with a finger or a thumb of his right or left hand until he sees a specific desired visual cue. That electrical pushbutton switch is monitored by the delay box. As long as the race car driver holds the pushbutton depressed the delay box sends 12 Volts DC (or 16VDC) at many Amperes to the race car's transmission (where an internal electromagnetic solenoid located in or on the transmission energizes, which in turn positions a spool valve that directs hydraulic fluid pressure in the transmission valvebody that locks the transmission in forward and reverse gears at the same time).

When the transbrake is engaged at the drag race track starting line (driver holding the pushbutton depressed), the car is held stationary regardless of how much engine power is applied to the drive line. The driver typically applies full throttle at this time, and the car remains stationary at the starting line under full engine power. When the driver sees the desired visual cue before him, the driver promptly releases his finger (or thumb) from the pushbutton. This button release opens the contacts within the pushbutton switch signaling the delay box and the delay box now begins an internal countdown. When the countdown timer reaches zero, the delay box stops current flowing to the solenoid in the transmission and that causes the spool valve to return to its normal position. With the spool valve in its normal position hydraulic fluid pressure in the transmission is removed from the reverse clutch pack (but maintained in the forward clutch pack), this causes the drag race car to "launch" (often with great thrust) from the starting line, accelerating rapidly forward toward the finish line.