Slow Down and Check Your Brakes
Every year, the Commercial Vehicle Safety Alliance (CVSA) observes Brake Safety Week. This is a great time for businesses to educate their drivers and reduce safety violations relating to faulty brakes in their vehicles.
Well–functioning brakes are the most important safety feature of a vehicle. Brake systems help ensure that drivers, passengers, and pedestrians remain safe while traveling. To reduce the chance of a preventable accident, business owners should enforce the maintenance and inspection of their vehicles.
Parts of a Braking System
Modern braking systems use pneumatics and friction to convert the pressure that a driver applies to the pedal to the force needed to stop the truck.
The Pedal — Depressing the pedal sends force from your foot to a hydraulic system. The size and shape of the pedal helps to increase the force before engaging the hydraulics.
The Master Cylinder and Combo Valve — The hydraulic system consists of fluid, pipes, and pistons. When the pistons are engaged, the force you applied is multiplied.
The Brake Lines — These connect the pedal and master cylinder to the brakes themselves. The fluid inside the lines travels to the brakes in the wheels, where it engages more pistons.
Disc Brakes — Usually mounted in the front wheels, but sometimes also in the back, disc brakes are standard on most private passenger vehicles. Once the disc brakes are engaged, the brake pads squeeze against the wheel. This creates friction that slows down the vehicle.
Drum Brakes — Usually mounted in the back wheels, drum brakes have more parts than disc brakes but operate similarly with friction. The additional components, including springs, help to apply more force to the brake pads.
Brake Shoes — These crescent–shaped parts of a drum brake push against the inside of the drum, generating the friction needed to stop the vehicle.
Air Brakes — Common in large and heavy vehicles, air brakes use compressed air instead of fluid. An air brake contains three braking systems: the service brake, the parking brake, and the emergency brake.
Emergency Brake — This mechanical brake operates separately from the main braking system. Connected to the back wheels, the emergency brake can help a vehicle come to an emergency stop or prevent it from rolling down a hill.
Anti–lock Braking System (ABS) — This feature prevents your brakes from locking up. An ABS sensor detects your speed, and its pistons and valves pump the brakes when you apply heavy pressure. This helps to reduce the car’s chance of skidding or spinning.
Plus, newer cars have more components to help prevent total brake failures.
Symptoms of Brake Issues
If your steering wheel vibrates when braking, your brakes may have rotor wear.
If it takes a lot of effort to press the foot pedal, or if you must press the pedal almost to the floor before it engages, there is a major issue that requires immediate attention.
Screeching, grinding, or squealing noises can be signs of faded brake pads or worn shoes on drum brakes.
If your vehicle pulls to one side when braking, your brake pads may be uneven.
If the brake light is on in your dashboard, the car is detecting an issue within the braking system.
For any of these symptoms, schedule maintenance with a certified repair technician.
Commercial Vehicle Pre-Trip Inspections
It is important to maintain braking systems and to be vigilant to potential issues.
Before every trip, commercial drivers should inspect their brakes as part of a full–vehicle inspection:
Check under the vehicle for leaks. A slow leak of fluid in the brake lines can make your brakes degrade over time; a major leak can lead to a total brake failure.
Check for missing, bent, or broken spacers, studs, clamps, or lugs. Confirm the tires are all the same type, properly inflated, and evenly matched.
Check for cracked drums, shoes or pads with fluid on them, or shoes worn thin, missing, or broken.
Anti–lock Braking System (ABS)
After starting the vehicle, check that the indicator light on your dashboard for the ABS turns off. If it does not turn off, something is wrong.
Brake pedal and trailer brake
Check for looseness, sticking, or damage. With your seatbelt fastened, drive about five miles per hour and push the brake. If the vehicle pulls to one side, stopping is delayed, or something feels “off,” there may be issues.
With your seatbelt fastened, set the parking brake and place the vehicle in low gear. Gently pull the parking brake and confirm that it holds. Do not drive with the parking brake engaged or you could cause damage to the braking system.
Hydraulic brake, if present
Pump the brake pedal three times, then press it for five seconds. If the pedal moves, there may be an issue.
Air brake, if present
In the engine compartment, check the condition and tightness of the Air Compressor Drive Belt.
With the vehicle parked but the parking brake disengaged, walk around the truck and check the slack adjusters. If a slack adjuster moves more than an inch, there may be a mechanical problem within the brake. This requires professional repairs.
Check the brake drums or discs, linings, and hoses for cracks, looseness, fluids, broken or missing parts, and wear.
Check the air compressor governor cut–in and cut–out pressures. Pumping should start around 100 psi and stop around 125 psi, depending on the vehicle.
Check the air pressure buildup rate. Air pressure should build from 50 to 90 psi in 3 minutes. Check the manufacturer’s guidelines, as the expectations vary by vehicle.
Test the air leakage rate by turning off the engine, releasing the parking brake, and timing the air pressure drop.
Confirm the low pressure warning signal is working correctly. Turn the engine off and the electrical power on. Step on and off the brake to manually reduce the air take pressure. The warning signal should activate before the pressure drops below 55 psi.
Check the spring brakes by fanning the air pressure down to 20–45 psi. This should trigger the spring brakes.
Check the air pressure buildup rate and parking brake, as described above.
Test the service brakes as described for the brake pedal and trailer brake.
Have a certified inspector evaluate your commercial vehicle at least every 6 months. Drum brakes require periodic cleaning to remove dust. Emergency brakes may need to be tightened. Both disc and drum brakes will deteriorate over time, and you should expect to repair or replace them every 35,000 to 70,000 miles or so.
Austin, A. (Aug. 2018). “7 Safety Tips for Brake Safety Awareness Month.” Beurkle Honda.
“CDL Pre–Trip Inspection: Brake Check.” (Dec. 2017). CDL Digest.
“Commercial Driver License Manual: Requirements for Licensing in New Jersey.” (2017). New Jersey Motor Vehicle Commission. PDF.
“How Do Car Braking Systems Work?” (Aug. 2021). Universal Technical Institute.
Nice, K. (n.d.) “How Brakes Work.” How Stuff Works.
The information contained in this article should not be construed as professional advice, and is not intended to replace official sources. Other resources linked from these pages are maintained by independent providers; therefore, NJM cannot guarantee their accuracy