The brake system on a commercial motor vehicle (CMV) must perform constantly and under all conditions. While both air disc brakes and S-cam drum brakes can get the job done, many manufacturers have made air disc brakes standard and the adoption rate for air disc brakes is increasing.

“The biggest difference between air disc brakes and S-cam drum brakes is disc brakes have a shorter stopping distance and you eliminate several components, so there are less maintenance items on air disc brakes,” said Chris Hough, vice president of maintenance at Penske Truck Leasing.

For example, air disc brakes do not need a slack adjuster, but S-cam brakes do. Kerri Wirachowsky, director of inspection programs for the Commercial Vehicle Safety Alliance (CVSA), said brakes out of adjustment is the number one violation drivers receive.

“Generally, when a vehicle is put out of service for brakes being out of adjustment, it is because the automatic slack adjuster did not adjust correctly. It could be because it was not maintained or because it failed,” Hough said.

Additionally, air disc brakes don’t experience brake fade, or result in stopping power, after repeated use. At higher speeds, disc brakes have a better response at higher temperatures.

Initially, the adoption of air disc brakes was slower because they were more expensive and roadside service didn’t always have parts, Wirachowsky said. “As more and more get introduced into the market, the more the price comes down and the more familiar technicians get with them and can do roadside repair. I think over the course of time, we’re going to see more go that way,” Wirachowsky said.

Penske Truck Leasing made air disc brakes standard on tractors within its rental fleet in 2017, and Hough expects to see increased adoption on trailers as well. “Over time, as technology continues to improve and air disc brakes become more economical, which they are, we’ll probably see the industry transition to air disc brakes on trailers,” Hough said.

Brake Maintenance

When maintained and installed correctly, both brake types meet required safety standards, but maintenance is critical for all systems. Disc brakes are sometimes erroneously characterized as being maintenance free and they are not, and brake systems, whether they are disc brakes or drum brakes, require attention.

Hough said brakes must be checked at every preventive maintenance inspection and drivers should regularly check brakes during pre- and post-trip inspections. Plus, brakes need to be lubricated or greased at set intervals and slack adjusters on S-cam drum brakes have to be tested.

“During a PM inspection, we measure the applied brake stroke. With the foot pedal applied, we measure the total distance the slack adjuster is traveling so we know it is working correctly,” Hough said. “They’re dependable, but from time to time, one will fail.”

Hoses and tubing have been an important focus area for CVSA inspectors for several years because brake hose chafing is another common violation. “You could have belly hoses on the trailer that are rubbing or the gladhand hoses are too long and they rub on the catwalk,” Wirachowsky said. “That is what we look for, and drivers should be looking for that during their inspection.”

If a hose rubs up against something until it punctures the liner of the hose, it will leak air. “If it is leaking air, the brakes won’t work correctly,” Hough said, adding that some hoses are difficult for drivers to inspect during pre- and post-trip inspections. “That is why it is so important during a PM inspection to check for any type of chafing.”

Overall Safety

According to the Federal Motor Carrier Safety Administration’s (FMCSA’s) latest Large Truck and Bus Crash Facts report, the brake system was the third most cited vehicle-related factor in fatal commercial motor vehicle and passenger vehicle crashes, highlighting the critical safety role brakes play in transportation.

Additionally, brake-related violations accounted for eight out of the top 20 vehicle violations in 2022, according to FMCSA’s Motor Carrier Management Information System. Plus, brake-related violations make up the largest percentage of all out-of-service violations cited during roadside inspections, CVSA reported.

Additional Information

CVSA has several brake sources available:

    Federal law has required professional truck drivers to wear seat belts since 1970, and a record 86% of professional drivers use safety belts, the Federal Motor Carrier Safety Administration (FMCSA) reported. According to FMCSA, safety belt use remains one of the cheapest, easiest and most important means to protect commercial motor vehicle drivers.

    [Read more...]Show less

    Warmer weather means commercial motor vehicle (CMV) drivers will be dealing with crowded streets and highways. Since warmer weather also brings out more bicyclists, pedestrians and children at play, professional drivers must use extra caution. Use these 7 tips to share the road safely with bicycles, pedestrians and children.

    1. Remember that bicycles are vehicles. Cyclists are asked to follow the same traffic laws as cars and trucks, so show them the same respect you would another driver. Yield to them as directed at stop signs, stop lights and intersections. Always give bicycles at least three feet of clearance before passing and watch for cyclists when you're getting in and out of your truck.

    2. Be cautious making left and right turns. You know your tractor-trailer needs to make wide right-hand turns. Pedestrians, cyclists and children at play may not know this so take extra caution when making any right-hand turns. The same is true for left-hand turns—always look for pedestrians or cyclists before crossing traffic.

    3. Watch crosswalks. Pedestrians have the right-of-way in crosswalks. If you're traveling through a neighborhood with crosswalks, drive slowly and be prepared to stop. Remember that on average trucks traveling 65 mph need two football fields to come to a complete rest, according to the Federal Motor Carrier Safety Administration (FMCSA).

    4. Know your limitations. Because your truck sits high, you may not see children at play or cyclists. They may be hidden by your truck's blind spots, or they could be playing behind your truck.

    5. Stay extra-alert between 6 – 9 p.m. That's when more than one-fifth (21%) of fatal bicycle-motor vehicle crashes happen, according to the Insurance Institute for Highway Safety. July and August run the highest risk for these types of accidents.

    6. Slow down. Children don't only cross the street using crosswalks. Cyclists don't always use reflectors or wear brightly colored clothing. Pedestrians don't always use flashlights when walking at night. Reducing your speed will help you be ready for anything.

    7. Don't drive distracted. Busier roads mean more potential for danger. So never call, text or email while driving. And never drive after drinking alcohol. This is against FMCSA regulation.

    As the Memorial Day holiday is set to shift into high gear, drivers – including do-it-yourself movers – are encouraged to pack a little patience for the road.

    [Read more...]Show less

    FMCSA. CSA. DOT. IRS. NHTSA. Federal, state and local regulations. They all need attention, and just keeping up is a full-time job.

    Drivers and fleet owners must be assessed under the FMCSA Compliance, Safety and Accountability (CSA) program. Owners have to ensure their vehicle assessments are performed and reported correctly when required. Large fleet or small, this is time consuming, and you’ll run into major risks if you miss something.

    Penske can help you stay on top of all federal, state and local regulations. We simplify compliance and provide expert assistance with:

    • Online guides, including safety and compliance information via Fleet Insight™
    • Regulatory compliance training
    • Federal, state and local tax management
    • Licensing, registration and permitting
    • Risk mitigation and administration
    • Mock audits and audit support

    Preventive Maintenance and Compliance

    Penske takes care of the maintenance portion of the CSA assessment every time one of your trucks comes in for its regularly scheduled preventive maintenance. We also handle all the reporting and submissions, meaning less paperwork and hassle for you and your drivers.

    Simplify With Fleet Insight

    Fleet Insight, our online suite of fleet management tools, is the one stop for simplifying your safety and compliance efforts. It contains:

    • Federal, state and local motor carrier safety regulations
    • Downloadable handbooks, manuals, forms and documents
    • Guides to safety and compliance documentation
    • Instructional webinars for management and drivers
    • Simulated DOT educational compliance reviews
    • FMCSA registration links