I think a transbrake works like this. The trans engages first gear and reverse at the same time. This is done with a different valve body, heavier duty clutches, and increased line pressures. When you release your trans brake button, a solinoid releases the reverse gear clutches and then your first gear clutches are the only ones engaged and you launch violently lifting the front of your car about two feet in the air, making the crowd go wild... 
