Braking Points

The brake pedal multiples...        read full caption The brake pedal multiples your leg’s “push” via leverage—the pedal length from the push-point to the pivot point is longer than the distance from the pivot to the master cylinder pushrod. This GM pedal has two pivot holes; the lower hole reduces the pedal ratio (leverage) when using power-assist.

Drum brakes use a residual...        read full caption Drum brakes use a residual pressure valve (RPV) that maintains 7-10-psi line-pressure to compensate for return spring tension. In-line ones like this are available from the aftermarket. In a stock M/C the RPV is located behind the outlet port’s flare-seat. If a drum-brake M/C has enough fluid capacity, it can be used with disc brakes by removing the RPV.

Cars with front discs/rear...        read full caption Cars with front discs/rear drums or different-size tires need a proportioning valve to fine-tune brake balance. Stock nonadjustable valves kick in after system pressure reaches a preselected level, then deliver a set brake-fluid percentage to the front or rear brakes. Adjustable valves like Baer’s allow varying the cut-in point. Keep in mind that a prop valve doesn’t reduce pressure in the system, only the rate at which fluid is applied to the rear brakes.

Stock brake systems are designed for stock cars. Whenever you change the total vehicle weight or the distribution of that weight, raise or lower the center of gravity, install “big ’n’ little” rubber, or drive down the racetrack, the design specs of the factory system may be exceeded. Many times, the system can be adjusted to compensate. But sometimes the only solution is to modify or custom-build a braking system that is fine-tuned for the particular application. To accomplish this, you need to determine both the vehicle’s actual braking requirements and whether a given disc/caliper combo is capable of fulfilling those requirements. The master-cylinder and brake-pedal assembly in turn must be able to supply sufficient volume and pressure to support the calipers and rotors. Brake system design is not based on magical formulas, but on sound scientific principles. Although we car crafters often consider brakes merely an afterthought, as power goes up, so must brake capability. And to realize the full potential of improved brakes, the suspension, wheel, and tire combo must also be up to the job.