What Is a Trans-Brake and Why Would I Need One?
A friend of mine is building a car to do some drag racing with and we had a bit of a Q&A session the other day. He’s not very knowledgeable about cars, yet, but he’s been doing lots of reading lately. One of the articles he read mentioned a trans-brake but didn’t do much to explain what it is and why a drag racer would need one. Not to make fun, but the descriptions he read led him to believe that it was something that helps the car slow down at the end of the run. It’s not. We’re here to talk about what a trans-brake does and how it can help your ride.
First to Clear Up Some Other Confusion Regarding Trans-Brakes
In our conversation my friend also mentioned something called a line lock and mentioned that it sounds as though it is something very similar. A line lock is a system that is installed in the front brake system to assist with keeping the car stationary when staged and/or to lock the front wheels to make doing a burnout to heat your rear tires easier. Some people think they’re the same thing or one requires the other. They aren’t the same and you can run one without the other.
With a line lock system the driver presses the brake pedal to engage the brakes, then engages the line lock and releases the brake pedal. The front brakes remain engaged so the driver can mat the gas, usually working the clutch at the same time (but not always). The line lock maintains brake pressure in the front brakes until being disengaged when the button is released.
The problem with a line lock is that it locks up the brake system. Some residual pressure is maintained in the rear brakes which must be overcome in order to perform the burnout. This can cause problems down the road in the brake system. If the pressure release isn’t instantaneous, the pressure in the front brakes must also be overcome, which will slow you down. We used to used line locks to impress the girls with tire smoke.
Another Type of Line Lock that Was Once Used
I used to own an old truck that had the emergency brake system as part of the driveshaft. The cable pulled a lever that tightened a belt around a drum on the front of the driveshaft. When I was growing up, older racers used to modify these so they would work on their dragsters. Pull the handle, tightening the band on the driveshaft locking it in place, shift into gear, mat the gas, and wait for the green with your right hand on the brake handle. But these tended to slip or drag on the driveshaft while it was turning and rob horsepower and torque. However, I do believe this system is what caused some genius to come up with the trans-brake.
Real Drag Racers Use a Trans-Brake
The trans-brake allows the driver to mat the gas and not have to hold the brakes. When the light turns green or the flag drops, the trans-brake is released and away you go at full throttle right away. Without the trans-brake, you’ve got to hold the brake to keep the care from rolling through the staging beams. Without the trans-brake, you can’t get the best launch your car is capable of.
What a Trans-Brake Is and How It Operates
A trans-brake is a component that is installed in your automatic transmission’s valve body. It’s a solenoid, or an electric valve that controls the flow of hydraulic fluid or the position of other valves. The driver places the shifter in gear and engages that trans-brake.
When the trans-brake engages, it makes the automatic transmission “think” that it is in both drive and reverse at the same time. This “confusion” allows you to mat the gas, get the engine spinning at full throttle, while also loading the torque converter. When the tree goes green or the flag drops, all you’ve got to do is let go of the button.
When you release the button on the trans-brake, you should already have the engine spinning at max RPM. This means that max torque is also be translated to the torque converter and into the transmission. With the trans-brake engaged, that torque is working at equal and opposite purposes, trying to drive the car both forward and back at the same time.
When you release the button, max torque and max horsepower are instantly translated to the rear wheels. There’s no lag in waiting for you to mash the pedal and the engine to come up to speed. It’s already at full speed and waiting for you to release the horses.
What This Means on the Track
Admittedly, if you’ve done your homework correctly and built a monster of an engine for your strip burner, there isn’t much lag from above high idle to full throttle. However, when you realize that the difference between the winner’s ribbon/trophy and watching the awards ceremony from your hauler can be ten thousandths of a second, the second or two difference is the difference between glory and honor and “just being there.”
We’re not putting these strip burning monsters together to come home empty-handed after a weekend at the track. We’re looking for something. Whether it’s accolades, respect, money, or, my favorite, pink slips, we’re looking for something. We need every advantage our money can buy.
The trans-brake is one of those advantages. If you’re serious about drag racing, you’ve got to have one. It can be the edge that makes the difference between having to go through the onerous tribulation of registering a car you just won at the Grudge Match at the DMV and signing your title over to the guy that did spend the money on the trans-brake.
Let’s go through this again. You shift the automatic transmission into gear, let’s call it Drive. You then press the button for the trans-brake (mine’s mounted right there on the shifter for convenience.) and engage the trans-brake. Mat the gas and get the engine producing max output. Wind it up tight. Watch the lights. Green light! Release the button and release the hounds! You’ve got everything your engine can produce. Right now. Not 1.3 seconds from now. Now. This instant. And you know what that means? Your competition is looking at your tail lights. Your time slip shows you’ve got the better R.T. (reaction time-the time between the tree going green and your car starting to move) as well as the best E.T. (Elapsed time-the time it takes for you to go the length of the track.). You’ve won!
Now the Bad News
Strangely enough, trans-brakes are pretty cheap, usually running right around 120 bucks. I say strangely for a couple reasons. The first is the advantage they can give is huge. The second is that I would normally expect a part that can cause so much internal damage to your transmission over time to be much more expensive. Especially when the damage that cheap little part can cause over time can be catastrophic.
When you plan on running a trans-brake, you need to tell your trans builder so they can take steps to beef up the internals of your transmission even more than your monster engine’s horsepower and torque output call for. This is because of the mechanical advantage that the trans-brake delivers.
The trans-brake basically makes the transmission try and tear itself apart. That’s because it tricks the transmission into thinking it’s in both Drive and Reverse at the same time. This causes torque to be equally split between trying to make the car go forward and reverse at the same time.
Automatic transmissions are designed to gradually transmit the torque generated by the engine to the driveshaft and thus to the wheels. This is even true for transmissions that are abused, I mean driven, by people like me that almost always mat the gas at the light. Even though I mat the gas, torque is allowed to build up instead of being instantly transmitted.
With a trans-brake, not so much. One infinitesimally small instant in time, the engine is spinning the front of the transmission and the trans-brake has the transmission internals working at cross-purposed. This is intensely stressful for the transmission. Then, in less time than it takes to snap your fingers, every individual horsepower and pound-foot of torque is instantly transmitted through the transmission, putting even more intensely severe stresses on the transmission. Sometimes the transmission isn’t able to handle that much stress and it literally snaps. We call it grenading because it causes lots of dangerous shrapnel. There are companies like Rossler Transmissions that build transmissions extra heavy duty so this doesn’t happen.