Transbrake Mechanism in Drag Racing

In motorsports, a good start frequently turns out to be the key to success, and this is particularly true for drag racing, where cars cover the whole distance within seconds. Many nonprofessional drag racing admirers must wonder how drag racers manage to take off so fast. In this article, we will consider a special mechanism named transbrake, which does the trick.

In drag racing, the introduction of a transbrake allowed racers on automatic cars to compete on equal footing with manually shifted cars. This mechanism helps a racer to keep the race car unmoved before the start as if the pedal brake is engaged. The transbrake unit is specifically intended for automatic gearboxes equipped with a torque converter (TC), where it is advantageous to accumulate hydraulic pressure before the car takes off. When the start command is given, the transbrake button is released by a driver and his car takes off at full throttle. Without this smart and simple mechanism, drivers have to engage the brake pedal to keep the car from a false start. The transbrake ensures the best launch a drag racing car is capable of.

Check out how the car starts with the help of transbrake

Before the introduction of the transbrake, racers driving the cars equipped with automatic gearboxes had to use the pedal brakes. Racers with manual cars had a significant advantage, as they just had to switch on the line lock (Roll Control) to start consistently at an engine RPM where the car operates in the most efficient manner. Then the transbrake was designed. This then-sophisticated solution allowed automatic racing cars to consistently take off at a quite high RPM rate and consequently have good chances of winning. To put it shortly, the transbrake leveled chances of automatically and manually shifted cars and attracted more fans to this fascinating type of racing.

What a TransBrake Is and How It Operates

A transbrake is a special element that is embedded in the valve body of the dragster’s automatic gear shifting mechanism. In fact, it is a solenoid, or an electric valve that keeps track of the ATF flow or positioning of other valves. When cars take their positions near the start line, racers put into gear and activate the transbrake.

TCI transbrake solenoid

Valve body with a transbrake solenoid installed

This mechanism is activated by pressing a special button, which sends an electric current to the solenoid in the valve body. The transbrake button is commonly mounted on the shifter, the steering wheel, or on the dashboard.

Transbrake button

Transbrake button on the steering wheel

When the transbrake switches on, it makes the transmission engage 1-st and R gears at the same time. However, it should be mentioned that some transbrakes engage 1-st and 2-nd gears simultaneously (rather than 1-st and reverse) for safety reasons. And it makes sense, let us assume that if something goes wrong when the transbrake engages 1-st and R gears the car may start moving backwards, when everyone is assuming if you are about to launch it’s going to go forwards.

Great videos about the transbrake mechanism and its operating principle

Simultaneous engagement of two gears forces the engine rotating at full throttle, while also loading the TC unit. With the gearbox input-shaft actually blocked, the driver then presses the gas pedal to the floor, forcing the TC to start slipping until its maximum stall speed is gained. When the start signal is given, the driver just has to release the button.

When the driver releases the transbrake button, the car engine reaches its maximum RPM rate. This means that maximum torque will be transmitted to the TC and into the gearbox. With the transbrake is actuated, that torque is working at 2 contradictory to each other tasks, forcing the car move in opposite directions at the same time.

Transbrake and reaction time

There have been numerous debates related to reaction times with a transbrake. Indeed, some racers are quicker than others, but some experts claim that there are numerous factors that can affect reaction times, including the following:

• Type of the transbrake button and its positioning
• Release speed of the transbrake
• Car dimensions
• hp and RPM rates of the engine at which the maximum torque is provided
• Main parameters of the TC unit
• Gear ratios
• Designs of chassis and suspension systems
• Size of the front tires
• Track surface state

Negative side of transbrake

It is interesting to point out that trans-brake solenoids are not very expensive (about $100-140), bearing in mind a significant advantage they provide for automatic racing cars. But most importantly, amateur drag racers do not always know that transbrake mechanisms, due to its peculiarities of operation, can lead to significant damages inside the transmission.

Thus, professional drag racing teams have to undertake specific measures on strengthening transmission units installed on their cars to deal with enhanced loads they are exposed to. This is because of the mechanical advantage that the transbrake provides. In fact, the transbrake mechanism severely overloads the transmission unit by simultaneous engagement of D and R gears. As a result, torque is equally distributed for making the car go in different directions simultaneously.

TH400 TransBrake transmission built to withstand severe loads

Basically, automatics are intended for step-by-step transfer of torque provided by the engine to the driveshaft and subsequently to the wheels. Therefore, when racers push on the transbrake button, the transmission deviates from its common principle of operation, thereby putting transmission internals under stressful operating conditions. But the most severe loads affect the transmission components when the driver disengages the transbrake button and all accumulated torque is transferred via thegearbox. In some cases, drag racing transmissions with trans-brakes just cannot withstand severe loads. Sometimes automatic gear shifting units are unable to handle that much stress and it literally snaps. Fortunately, there are companies specialized in production of modified transmission and modification of other car components to ensure that the car will be capable of operating under heavy loads.

Proper Transbrake Use and Maintenance

Most brake mechanisms only operate in 1-st gear. This means if drivers accidentally hit the switch while the car is in higher gears, the corresponding solenoid won’t be actuated. When activating the transbrake system, this will only work when the car is completely halted. Under certain circumstances, drivers may prefer to take the car off by means of the pedal brake instead of the transbrake. In such a case, it is necessary to disconnect the power supply switch and there will be no negative impact on the gearbox.

Transbrake Kit

If the transbrake mechanism operates with some lagging when the button is released, then it is required to check out the ATF state. ATF shortages usually lead to some lagging issues. If the ATF level is OK, then it is necessary to pay attention to the release switch. If it is not the case either, then you have to tear down the transbrake solenoid and make sure that it is not contaminated with dirt or debris.

All in all, it is not that hard to drive a racecar equipped with a transbrake, but it is necessary to bear in mind the main peculiarities of the transbrake operation in order to avoid harm to the transmission unit.