Got the GO? Now get the WHOA.
Let’s talk braking, stopping that built, boosted, nitrous-shotted, beauty of yours.
For safety, first; and because in racing, it is corner entry that separates the “Almost” from the “Winner.”
Until recently, any stock brake setup was woefully inadequate for track work, or even an aggressive canyon run.
And classic cars? Forget it.
Your first step in an equipment upgrade is a set of aggressive brake pads that can take the heat, and brake fluid that can stand heavy duty driving and not boil. Boiling fluid is incredibly dangerous, even worse than fading pads. For track work, always work to have brake cooling ducts or even deflectors to direct cool air to the inside of the front rotors, especially.
You are driving hard, and you don’t like the way the brakes feel. Here are possible scenarios, in order of urgency. First, before we even leave the parking spot, say you feel a soft pedal.
No bueno, Driver.
Especially with the car running and generating vacuum for the booster, the pedal should travel a bit and then firm up nicely. If not, look at the pads through the wheel or with it off. Do they look thin or show angle wear? Typically, the thinner the material, the further out the pistons are from the caliper, and the softer the pedal.
Likewise, the more grooves in the rotor, the softer the pedal.
Small surface cracks are common and not a problem in hard driving, but deeper cracks are. If the crack goes all the way through? Get that brake rotor off of there, it’s done.
Next, bleed the calipers. Is the fluid full and clear? Brake fluid absorbs water and turns dark; and then makes the pedal soft. While you have a wheel in the air, check for wheel bearing play, also a cause of a soft pedal.
Further, do you have ABS? The modulators have their own special tools and process, and need to be flushed and bled as well.
I think this is the problem on my Tundra tow vehicle right now. New top-quality Hawk LTS truck pads, Talon rotors, and HP 520 fluid, and two bleed outs, have failed to get proper pedal response. I can feel that there is still air in the system.
Here are some hints for brake trouble: If pedal travel gets suddenly longer on track, or goes completely to the floor, scaring the daylights outta you, then it’s likely the fluid has boiled. Boiling causes air bubbles, so even if you can back off, cool and get the pedal back, it will probably not be right again until you bleed it out with fresh fluid, and hopefully an upgrade to a racing fluid.
If the pedal is still up, but the car won’t stop, that’s brake fade. You push harder and harder and nothing more happens? That’s fade. You’ll need better cooling for either condition, and a pad with a higher heat range for fade.
In either of these conditions while driving, brake earlier and less, cool the brakes, or big trouble is coming. Most systems will feel worse and worse before they fail completely. Take heed of a changing brake pedal feel on track or in the mountains.
Something is getting too hot. Listen to what your car is telling you:
“Back off, Driver!”
When you modify the brakes in your hot rod, and especially building from scratch, it is of great importance to get the bias front-to-rear correct. Under hard braking, the fronts should start to lock up just before the rears. The danger to watch out for is rear bias; the rear brakes locking first. If that happens, your machine will get sideways and possibly spin (If you didn’t, read my earlier article on car control here.)
The best systems like Baer Brakes include a bias adjusting knob. If your car is not equipped, you can also adjust bias with differing pad compounds. Find many options at SummitRacing.com. Hawk has a wide range of compounds.
To check bias is a tricky operation, but critical to the safety of your car in emergency stopping. In normal smooth street stops, you often will never notice, but a sudden hard avoidance situation is NOT the time to find out. Find a safe place on clean pavement to test stops with no traffic and nothing to hit if your car gets twitchy. Start at just 30 or maybe 40 mph. Driving straight and steady, smoothly and quickly brake harder and harder until you feel and hear a tire start to lock up. It is helpful to have an outside observer and even video to determine if front or rear locked first.
If the car pulls hard to one side then there could be air in one side, which will be the weak side, away from the direction of pull. Wheel misalignment and worn parts can also cause this, and so can the road surface. If your corner weights are unbalanced, that will also cause an early lockup on either end. Setting the weight on each wheel is race car stuff, but it can really mess up your handling if way off, which major builds often are. One way to tell if if the car oversteers in one direction and understeers in the other direction.
If the car goes straight when locking occurs, it’s the front. If it wants to get twitchy or sideways, then it’s the rear. Sneak up on it, away from traffic. I’d try a far corner of a big parking lot, or coming into a slow corner with no traffic around on a race track. You must figure out your bias to have a safe car in emergency or high-performance braking.
If you are taking your new build to the track for the first time, be aware that you could experience green fade. This is an extreme loss of brake bite when the pads get hot for the first time. Often you will smell them strongly just before the braking virtually disappears. Some pads come pre-burnished and won’t do this, other do not. The smell is a clue.
Most times the proper way to bed in brakes involves gradually bringing them up to a high temperature, to the point where you can feel fade, then cooling them off for a bit with little to no braking. Once cooled, they should no be ready for aggressive driving.
While we’re at it, never apply the handbrake after coming off track or a hot street run, and do not hold your foot on the pedal sitting still either. This can warp your rotors and or boil your brake fluid because the rotors stay hot at the pad area, and cool the rest of the way around. Put your car in gear if manual shift or Park with an automatic.
After a hard run, always give your brakes a chance to cool, even if driving slowly around the paddock or a parking lot. If you see smoke or smell brake, drive it around a bit to help cool.
This advice applies to your tow vehicle as well. If you’ve got a heavy load and are stopping downhill to a light or pullout, put the vehicle in park. Never hold pressure on the brake pedal when sitting still on hot brakes.
When heading out, always work to bring brake temperatures up a bit gradually. Common sense; it’s not good to slam on cold brakes straight out of the pits or into the canyon run. This is doubly true if you have any new parts not yet bedded, pads or rotors. Take a few corners or even laps to bring them up to temperature gradually, but do eventually get them good and hot to bed them in. Then cool them down some before stopping if you can.
This is also true of a Red Flag in a race situation.
Many times it means check your mirrors and come to a complete stop off to a side to the track, but still on the pavement. If the incident is not in your vision, stop gradually, to help cool a little, and to reduce the chance of impacts from the cars behind you. Remember you are part of a flow. And put the car in gear or Park here on track, too, to avoid heat soak and possibly boiling your fluid, just like in the paddock or on pit lane.
Repeating: do not hold pedal pressure on hot brakes sitting still.
Know that a lot of these lessons were learned the hard way. Most of my worst crashes were brake issues, like Ice Mode (Hard pedal no brakes: from 1990’s ABS on track). All of this advice will save you a lot of braking trouble, make you safer, and maybe even save you and your car from crashing.
And I haven’t even touched on brake techniques.
Watch OnAllCylinders for my next story on Brake like a Pro, or And You Thought The Brakes Were For Stopping?
What size booster is best at high altitude ( 5000′ ) .