If you’ve spent any time in hilly areas, you’ve probably seen warning signs advising you not to ride your brakes on those lengthy descents. But what’s really going on with your car, and what are the hidden dangers of riding your brakes?
The Modern Brake System
There are two types of brakes found on today’s passenger vehicles, caliper and drum. The same basic operational principles apply to both: when the brake pedal is pressed, fluid is sent to pressurize a mechanism (caliper or slave cylinder), which in turn squeezes or pushes a friction material (pads or shoes) against a metal component attached to the axle (rotor or drum). When enough pressure is applied, the vehicle slows and/or stops. A tremendous amount of friction is involved in stopping something as heavy as a moving vehicle, and the biggest byproduct of this process is heat.
Under normal driving conditions, this heat is able to dissipate as air moves over the rotors or drums, but riding your brakes puts the pads, or shoes, in constant contact with this metal surface. Even if the brakes aren’t fully applied, this constant friction builds heat around the surrounding components without getting a chance to cool down.
Short Term Risks
The biggest danger of riding your brakes is the possibility of generating so much heat the brake fluid actually boils. The reason fluid is used in the braking system in the first place is that it is in compressible, and thus transfers force directly from your foot. When it boils, however, gas bubbles form in the fluid, and the gas can be compressed. Under these conditions, pushing the pedal won’t build pressure in the system, and the brakes will fail. Brake fade can also occur when a large amount of heat causes a chemical reaction with the friction material itself, creating gas bubbles between pads and rotor, and these air pockets can reduce efficiency.
Long Term Effects
The short term effects of brake fade or all out loss are extremely dangerous. But even if you are lucky enough to avoid this terrifying situation, the long term effects of riding your brakes can create substantial maintenance issues. For starters, the friction material on pads and shoes is meant to wear down over time, but riding the brakes speeds up this process significantly. Over time, the heat buildup discussed earlier can also damage components not meant to handle that sort of stress on a regular basis. Rotors can warp, impacting braking ability and unevenly wearing pads. Non-metallic parts such as caliper seals and dust boots can actually melt, causing leaks.
What to Do
On long downhill descents, downshift and let engine braking do the work. Yes, even automatics have this option. There are occasionally arguments made that this causes stress on your transmission, but the truth is that it’s not substantial wear and tear beyond what’s expected of a transmission in the first place, and it is most certainly a better move than one that could cause you to lose your brakes. If you still need to use the brakes to slow the vehicle, opt for a punctuated, more forceful brake application instead of keeping your foot lightly on the pedal. This gives them a better chance to cool off.
For more information on your brakes, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photo courtesy Wikimedia Commons
Source: NAPA Know How