The old saying goes, "It's better to stop short, than not to stop at all." Okay, we just made that up, but it applies perfectly to this story's topic: better brakes. In the past we've shown you how to install some great aftermarket brake kits that will yank the fillings from your teeth when you stomp on the whoa pedal, but this time we wanted to tell you how to reach the full potential of your car's brakes. We searched far and wide to find cures for some common brake system ailments and learned a few tricks to decrease your car's stopping distances at the same time.
Stopping Is Hot
What happens when you slam on the brake pedal and your car comes to a screeching halt? The kinetic energy of your car moving forward is converted into heat, which is then dissipated into the atmosphere through the brake rotors and pads. And it is this heat that is the number one killer of brakes. That is, unless you neglect your brake system for a very long time, like by doing something as awful as not flushing your brake fluid once a year, SHAME! Even the best brakes and fluid will not function without adequate cooling. In fact the more serious your brake system is, the more attention needs to be directed to proper cooling, as the brakes will generate more heat due to their increased capacity.
The best way to improve the stopping of your factory car IS NOT by installing a rear disc brake kit first. Bigger front brakes are the best way to repeatedly stop your car in a short distance. Swap out those tiny 10-inch front rotors for a set of 11 inchers and you'll feel a noticeable difference right away. Along with the rotor swap, you'll probably have to swap spindles, calipers, and maybe the master cylinder too, but small brakes are not the only reason a car won't stop. There are many reasons for brake system inadequacies, most of which are caused by inexperienced, first-time brake swappers.
The Fix Is In Here
To get the definitive answers to all our braking needs we turned to the experts at Baer Brakes, Master Power, Stainless Steel Brakes, and Wilwood. These companies have made it their life's work to figure out how to make your car stop shorter, and they've learned a lot in the process. Luckily for us they were more than willing to share, but at a price. And that cost was a free visit to their websites, where we found way more information than we could ever produce in one tiny article. So we'll give you the basics here, but you're on your own to do more research and cure your own problems. We can see the stop sign ahead. Shorter distances are in your future.
Troubleshooting Brake Problems
The experts at Baer Racing gave us a quick lesson in making a car stop better, regardless of what kind of brakes are on it. Baer recommends that the brake system be engineered so the master cylinder piston area is 12-19 percent of the total front caliper piston area (see Formula A: Calculating area of caliper and master cylinder pistons; Example 3). This is a good starting point to ensure that, hydraulically, your brake system will provide the correct volume and pressure under all conditions. Follow this up with careful on-the-road testing to determine if your brakes work effectively. When troubleshooting your brake system, you find that your ratios are correct, then virtually all brake performance issues can be traced back to improper actuation. Stock cars have the most basic actuation systems, usually combined with the correct ratios to provide adequate brake performance. It's when you blindly start modifying your vehicle that things can go wrong.
The following are a few tips to help you check your vehicle's brakes. These rules apply to all brake systems regardless of the manufacturer.
Problem: Soft Pedal Under Hard Use
The braking forces feel good under normal driving conditions but diminish quickly when the car is used aggressively (as on a track or in a panic situation) and it can't even lock up the wheels.
Possible Cause: Improper Pedal And Pushrod Geometry
With the pedal fully depressed the angle between the master cylinder and its pushrod must NEVER be less than 90 degrees (see Pushrod Geometry illustration below). If the angle falls to just 1 degree less than 90, brake pressure will decrease suddenly and dramatically. This condition is described as the pedal/pushrod assembly's being "over center."
Solution: Check And Correct The Angle
Use a small carpenter's or machinist's square to check that when the pedal is fully depressed, the effective angle between the pushrod and the pedal is never less than 90 degrees. If a visual check is not possible, measure the pressure at the caliper and look for a condition where pressure initially builds and then suddenly falls as the pedal is depressed farther. In some cases, lengthening the pushrod may alleviate this condition or it may be necessary to relocate some components to achieve the proper pedal geometry.
Special Note: When using a master cylinder that's too big (unfortunately, an all-too-common practice), it's possible that pedal travel may be reduced enough to hide an over-center condition. Then, when the master cylinder is replaced, the pedal movement is increased and an over-center problem becomes evident.
Problem: Extreme Brake Pedal Effort
The vehicle has a firm pedal, but it takes a great effort and serious leg muscles to get the car to stop.
Possible Cause 1: Improper Caliper To Master Cylinder Ratio
A simple hydraulic rule: When Volume Goes Up, Pressure Goes Down and vice versa. You must select a master cylinder that will provide the proper volume to actuate the system, while still delivering the correct pressure. A large-bore master cylinder will move more fluid but at a lower pressure. A small-bore master cylinder will create higher pressure but can't move as much fluid per stroke.
Solution 1: Optimize Piston Areas
Measure all caliper and master cylinder piston areas, re-specify master cylinder to 12-19 percent of the area of just one front caliper (see Formula A; Example 3).
Possible Cause 2: Engine Vacuum Too Low
Most vacuum boosters will produce good results only if at least 16-18 inches are available at idle.
Solution 2: Increase Vacuum
It is sometimes possible to make minor adjustments to the engine to maximize idle vacuum, but engines with even moderate performance camshafts can produce too little vacuum. In some cases it's possible to employ a master cylinder with slightly less piston area to give the system more pressure. Other alternatives include removing the vacuum booster and reconfiguring the pedal geometry for manual operation or converting to a "Hydra Boost" system (hydraulic booster driven off a pump, such as a power steering unit) or installing an electric vacuum pump, which is available from Master Power.
Possible Cause 3: Pedal Ratio Incorrect
The brake pedal ratio is determined by dividing the distance from the center of the pedal pivot to the center of the pedal pad in a straight line-see "Pedal Ratio" illustration. (Note: Most brake pedals are curved but do not calculate the curve).
Solution 3: Optimize Pedal Ratio
Measure pedal ratio and revise geometry to increase leverage. Many factory brake pedals come with two holes drilled in them, one for manual and one for power brakes. When switching between the two systems, it is important to use the correct pushrod hole. The general rule of pedal ratios with top pivots is: The hole closest to the pivot point makes more pressure but will need to travel farther to move the same volume of fluid, while the hole farthest away from the pivot point will make less pressure but will move more fluid per stroke. You can experiment with pedal ratios by drilling different holes, but pay attention to the pedal/pushrod geometry and don't go "over center." Wilwood Engineering says that a 6:1 pedal ratio is an ideal starting point. Master Power recommends a 4:1 for power brakes and 5:1 for manual brakes.
Problem: Rear Brakes Seem To Be Doing All The Work
This problem is common in cars which have rear disc brakes swapped in from a different car.
Cause: Rear Caliper Piston Area Greater Than Front
Brake balance front to rear can never be correctly adjusted when the rear piston area is larger than the front. No adjustable proportioning valve (or number of valves employed) can correct this problem. For proper performance the front caliper piston area must be at least 25 percent greater than the rear piston area, preferably closer to 40 percent (for reference; a stock '93-97 Camaro has a front piston area 55 percent greater than its rear).
Solution: Measure all caliper piston diameters and change front or rear calipers (and master cylinder if necessary) to achieve appropriate front-to-rear differential
Calculating AREA of caliper and master cylinder pistons.AREA = 3.1416 x (RADIUS x RADIUS)
Determine the area of a 15/16-inch (0.9375) bore master cylinder.
First establish the radius, which is half the diameter: 0.9375 / 2 = 0.4687So plug 0.4687 into the formula and get: 3.1416 x (0.4687 x 0.4687) = 0.6902 is the piston area of a 15/16-inch bore
Determine the area of a non-opposed two-piston, 1.5-inch diameter caliper.*Solve for area of each piston first, and then add both areas together.
Radius = 1.5 / 2 = 0.753.1416 x (0.75 x 0.75) = 1.7671 x 2 = 3.5342 is the area for both pistons combined.
Note: When calculating the area of a caliper with multiple, opposing pistons, Baer determines the area of only one bank of pistons for comparison purposes.
Divide the area of the master cylinder by the area of one front caliper to find your percentage.0.6902 / 3.5342 = 19.5%
When designing a brake system always shoot for a figure between 12-19 percent as a starting point, but that's only the beginning-final tuning on the road may determine a different size master cylinder is needed.
Bleeding Can Make You Stop Better
Bleeding brakes is not done with pressure: it is purely a function of moving fluid through the system. The object is to displace air, not to see how far you can squirt fluid out of the caliper! Enlist someone to help you bleed the brakes. Make sure they also read these instructions carefully and understand the goal.
This requires a properly sized box wrench for the bleeder screws and a clear plastic hose connected to a clear plastic container (a clean soda bottle works good). New brake fluid is also a must. Start by topping off the master cylinder with fresh fluid and pouring about 1-inch of fluid into your clear container. At the caliper farthest from the master cylinder attach one end of the clear plastic hose to the bleeder screw and run the other end of the plastic hose into the fresh brake fluid in your container. Open the bleeder screw and have your helper VERY SLOWLY push the brake pedal by hand until fluid comes out and then close the bleeder. Next, have your partner very slowly push the pedal again with modest pressure ONE TIME ONLY until hydraulic resistance is encountered. Ask your partner to hold at this point and notify you by saying that he is "holding." Open the bleeder using the same modest pressure, letting the pedal go to the floor or as far as it can until it stops, close the bleeder, notify your partner by saying, "sealed."
Repeat this bleeding sequence until all signs of air are purged (no bubbles) from the fluid. To avoid aerating the fluid, never stroke the pedal more than once and don't let the master cylinder run dry. Be sure to check fluid level often. Finally, carefully tap on the caliper with a block of wood or plastic hammer to dislodge any air bubbles that may be trapped and repeat the bleeding sequence once more.
Move to the wheel that is the next farthest from the master cylinder and repeat the procedure. Any time you open the brake system, it is advisable to repeat the bleeding process after driving the vehicle for a day, as driving may dislodge some additional air bubbles.
Note: Flushing your brake fluid yearly is a good practice to get into. Moisture is the number one killer of brake fluid, silicone fluids excepted (but the experts we spoke to agree that you should avoid that stuff like the plague). Open your master cylinder and look at the fluid. If it's black and murky, it's way past the time for a flush.
Whose Valve Is It Anyway?
When discussing brake systems, you'll often hear discussion of valves. But these are not of the intake and exhaust variety.
The techs at Master Power offered several brake valve definitions, which you should familiarize yourself with to better understand brake functions.
It is installed in-line to limit pressure to the rear brakes and control rear wheel lock up under heavy braking. Full pressure is always available to the front brakes when a proportioning valve is correctly installed. Most stock cars come with a non-adjustable proportioning valve, but replacing it with an adjustable proportioning valve can improve the braking of ANY car, regardless of what kind of brakes it has.
Metering ValveUsed on front disc/rear drum cars to better balance the front-to-rear brakes. A metering valve does not allow the front brake pressure to rise until the pressure at the rear drums has risen sufficiently to overcome the brake shoe return springs.
Residual Pressure Valve
A 10-pound valve installed in the master cylinder to maintain line pressure in rear drum brakes and keep the shoes close to the drums giving a higher, firmer pedal. A 2-pound valve is required inline to either the front or rear brakes whenever the master cylinder is mounted lower than the calipers. It prevents fluid backflow into the master cylinder.
A combination valve incorporates metering, proportioning, and a 10-pound residual into one valve. These are used on many OEM disc/drum systems.