Stopping Distance & Brake Performance Flashcards

What is 'mechanical brake fade' in an air brake system?

Answer: A condition where brake drums expand from heat so the shoes must travel farther to make contact, reducing braking force

Mechanical fade occurs when brake drums expand due to heat buildup, increasing the gap between the lining and drum so shoes cannot apply full force before reaching the end of available travel.

How does anti-lock braking system (ABS) affect the stopping distance of an air-braked commercial vehicle?

Answer: ABS prevents wheel lockup and helps maintain steering control but may not reduce overall stopping distance on all surfaces

ABS prevents wheel lockup to maintain steering control during hard braking, but on some surfaces ABS-equipped vehicles may have similar or only marginally shorter stopping distances — its main benefit is controllability.

If a trailer's brakes are completely out of service, what is the MOST accurate statement about stopping distance for the combination vehicle?

Answer: Stopping distance increases significantly because the tractor brakes must stop the full weight of both units

When trailer brakes fail, the tractor's brakes must decelerate the entire combination's weight, far exceeding their designed capacity and dramatically increasing stopping distance.

What effect does carrying a load that exceeds the vehicle's gross vehicle weight rating (GVWR) have on stopping distance?

Answer: It increases stopping distance because the brakes were not designed to stop that amount of weight

Brakes are engineered to stop a specific maximum weight; exceeding GVWR means the braking system must work beyond its designed capacity, substantially increasing stopping distance.

Which statement BEST describes why perception distance is a significant part of total stopping distance for commercial truck drivers?

Answer: Trucks have a higher seating position that can reduce visibility close to the vehicle, and recognizing a hazard can take longer at highway speeds

Higher seating positions create large blind spots near the truck, and at highway speeds objects are covered before the brain fully processes the danger, making perception a major factor in stopping distance.

How does altitude affect air brake stopping performance on vehicles operating in mountainous regions?

Answer: Higher altitude reduces air density, which can decrease engine braking effectiveness but does not directly affect brake chamber pressure

At higher altitudes, thinner air reduces engine compression braking and power, placing more demand on service brakes during descents, but brake chamber air pressure from the onboard compressor remains controlled by the governor.

During a pre-trip brake check, a driver finds that the service brake pushrod stroke on one rear axle is beyond the legal adjustment limit. What is the MOST accurate statement about stopping distance?

Answer: That brake assembly will apply with reduced force or not at all, increasing total stopping distance

A brake with pushrod stroke beyond the adjustment limit cannot generate full clamping force on the drum, contributing little or no braking effort and forcing other axles to compensate, increasing stopping distance.