A previous FAMA Forum article focused on air disc brake maintenance and the industry trend towards converting conventional drums to disc brake systems. This article will focus on the vehicles with conventional drum brake systems in service today and stress the importance of regular maintenance on these brake systems to ensure long-term safety and performance.
CHALLENGES
What challenges do fire departments and maintenance technicians face when specifying brakes on their vehicles?
One of the most important items to consider is the type of environment in which vehicles will be used and to make the right brake choices for that environment. For example, a vehicle subject to dirty, abrasive environments may see negative effects on pad and rotor life with disc brakes. However, for a fire department on emergency runs at higher speeds or mountain grades, air disc brakes may be the right solution. All applications requiring axle ratings of 29,000 pounds or more still need drum brakes due to current spindle design and packaging constraints. All of these factors should be considered when specifying a brake package.
BRAKE FADE
What is brake fade and how does it occur?
A brake’s fundamental job is to create friction, absorb energy and slow a vehicle. Brake fade occurs when it cannot absorb energy at the required rate, which generates excess heat. This heat causes a brake drum to expand away from the friction material of the brake, lessening the stopping power and overall performance of the brake. This fade can lead to uneven application of the brake, “wobbles” (vibrations) or worse.
BRAKE BURNISHING
We understand brake burnishing is an important maintenance step with drum brakes to assist in reducing brake fade and noise.
A common complaint with drum brake systems is excess noise and vibration. Burnishing the brakes can improve or eliminate this as it ensures proper seating of the friction material to the drum. The following steps should be performed each time a new brake friction or brake drum is installed, or can be performed as needed to help eliminate brake noise:
- Inspect for loose or broken components and proper brake setup.
- Drive the vehicle at speeds of 20-25 miles per hour while maintaining light application of the service brake and the throttle to maintain speed for a duration of 15-20 seconds. Release the service brake for 15 to 20 seconds and repeat.
- Stop the vehicle and evaluate brake temperatures with a handheld heat gun on the outside of the brake drum. A proper burnishing will occur at 450 degrees but should not exceed 550 degrees. Temperatures from side to side should not vary more than 50 degrees. Additional detail can be found on page 40 of Meritor’s Cam Brake and Slack Adjuster Maintenance Manual – MM4.1
DRIVER BEHAVIOR
Can driver behaviors be modified to reduce maintenance time and extend brake life?
Because of the nature of the job, emergency vehicles must get to their destinations as quickly and safely as possible. As a result, the vehicles’ brakes will be used aggressively. However, there is a difference between aggressive use and abuse, and this can make a difference in brake component life. Through continuous training, drivers will better understand the importance of monitoring for symptoms of brake-related issues. In addition to warning lights, drivers should watch for brake pull, decline in performance, vibrations when applying the brake, and unusual noises. Recognizing and reporting these conditions to maintenance personnel will extend overall brake life and alert technicians to potentially catastrophic failures before they happen.
INSPECTION BEST PRACTICES
Drum brakes require regular inspection to ensure consistent performance and optimal life. Inspection practices can vary between different systems, meaning it’s imperative to inspect based on the specific brakes of a vehicle. Although wheel-on inspections can reduce downtime by giving an overall picture of brake health, thorough brake inspections require removing the wheels.
REPLACEMENT PARTS
It’s extremely important to maintain brake systems with OEM parts. To meet regulatory stopping requirements, fire departments should purchase new brakes based on parameters established by vehicle manufacturers. If changes are made, such as using non-OE aftermarket parts, there is risk of upsetting the balanced brake system or creating unintended consequences. For example, changing one axle’s set of pads to a different friction formula runs the risk of overheating the other axle, causing fade which prevents the vehicle from meeting expected stopping distance.
FUTURE ADVANCES
As vehicles continue to evolve with advanced technology products, suppliers will be able to offer higher levels of diagnostics. The industry is getting more requests from customers for continuous monitoring of brake temperature and wheel-end conditions so they can evaluate when components require maintenance or replacement and schedule downtime more efficiently. These requests are taken into consideration when developing new products.
TRAINING
Meritor is a manufacturer of foundational brake solutions for the fire and rescue market, offering fleets disc and drum brake solutions to meet their needs. Meritor offers free training covering the full range of the company’s brakes and other products.
The Fire Apparatus Manufacturers’ Association (FAMA) is committed to the manufacture and sale of safe, efficient emergency response vehicles and equipment. FAMA urges fire departments to evaluate the full range of safety features offered by its member companies.
