Maintenance

How to Pinpoint and Prevent Common Brake Problems

Thomas McMahon
Posted on March 20, 2015

School buses face a variety of challenging operating conditions — frequent stops, hilly terrain, road salts, traffic, rural roads, etc. — that put stress on their braking systems, making preventive maintenance all the more important. Here, brake suppliers share best practices in inspecting and maintaining school bus brakes.

Thorough inspections
Complete brake inspections are essential to keeping school buses running safely. Lining condition, rotor plate thickness, brake hose flexibility and brake fluid condition are examples of service-related items that need to be inspected regularly, according to Wally Marciniak, director of training for Brake Parts Inc, supplier of the Raybestos brand of brake products.

“For example, brake fluid is hygroscopic — meaning it is intended to absorb moisture,” Marciniak says. “Too much moisture is problematic and could affect the overall integrity of the brake system.”

He adds that manufacturers’ recommendations and procedures should be practiced for all brake service work and component replacement.

Earl Gesch, original equipment (OE) sales and development engineering manager for Performance Friction, says that school bus technicians should also check the tone ring on a regular basis, looking out for corrosion.

Jim Baldwin, director of fleet sales for Marathon Brake Systems, provides some pointers for the inspection of air brakes:

• Look for cracked or bent brake chamber and camshaft support brackets.  
• Check air line hoses for kinks, chafing and cracks, and replace as needed.
• Remove and check the operation of the automatic brake adjusters to make sure they are operating properly. Refer to the manufacturer’s manual.
• Remove the camshaft and check the head for wear or flat spots. Check the bearing journals for rusting, pitted surfaces or excessive wear. Also, check the condition of the splines. Replace as necessary.

Common issues
Alexandra Cuthbert, bus sales manager for Performance Friction, says that common issues seen in school buses include unequal, uneven wear on brake pads and rotors due to calipers hanging up or pin sliders seizing. Another key issue is pads crumbling, which can be brought on by road de-icing agents such as magnesium chloride and calcium chloride.

“If you choose a brake pad that isn’t compatible with proper protection from debris and salts used to de-ice roads in your area, you can lose braking performance,” Cuthbert says.

Performance Friction uses an anti-corrosive coating on its brake pad backing plates to prevent issues with road salts. Gesch says those salts “can really accelerate the process of pad corrosion and rust jacking. Other than more frequent inspection, there’s not a whole lot you can do once that process starts.”

Brakes being out of adjustment is another common problem. Troy Flodin, foundation drum brake engineering manager for Bendix Spicer Foundation Brake, notes that various items can cause out-of-adjustment brakes: slacks, broken brake components, actuator issues, drum/hub issues, etc.

“Routine inspection of free stroke will help identify the issue,” Flodin says.

"The driver is the first line of defense in identifying braking issues since they are the closest to the vehicle on a daily basis."
Troy Flodin
Foundation Drum Brake Engineering Manager
Bendix Spicer Foundation Brake

Service tips
When service work is required, stopping distance should be measured, the brake system should be balanced and all components should be replaced for maximum safety, according to Marciniak of Brake Parts Inc.

“After any service work, the vehicle needs be test-driven to ensure safe and smooth operation,” Marciniak adds.

For air brake maintenance, Marathon’s recommendations include:

• Replace camshaft bushings.
• Replace the brake shoes with a premium friction material using new attaching hardware kits, which will include stainless steel anchor pin bushings, heavy duty return springs and new rollers.
• Install a new brake drum, making sure it is properly seated and centered on the hub tabs, and install the wheels/studs starting at the 12 o’clock position.
• To adjust the brakes, turn the adjusting bolt clockwise to “touch” the drum. Then back the adjuster away from the brake drum a half turn. Check for a free wheel rotation.
Kevin Pfost, who specializes in technical service at Bendix Spicer Foundation Brake, offers these tips for air brakes:
• Proper lubrication ensures proper function of the components and helps with the life and ease of disassembly. Do not over-grease.
• Perform air dryer maintenance once a year.
• Do not adjust automatic slack adjusters.
• Do not use any additives in the air system.
• Replace linings with OE replacement linings and new brake drums.

Drivers’ role
In addition to the shop staff, school bus drivers can play a key role in keeping brakes operating properly.

Marciniak of Brake Parts Inc says that drivers need to let technicians know if they notice any braking issues. Examples include a difference in pedal feel, excessive pedal travel, increased stopping distance, noise issues (including grinding or squealing) and brake-related warning lights. Any of those types of conditions should be referred to a technician for inspection and service.

Gesch of Performance Friction says that if a driver sees brake fluid on any brake components, “it’s an emergency situation. It could be caused by faulty seals or a compromised caliper. … That should be pretty rare, but it’s definitely cause for immediate attention.”

For buses with air brakes, drivers should be taught to drain the air tanks daily. They should also look and listen for air leaks and brake issues during their pre-trip inspection.

“The driver is the first line of defense in identifying braking issues since they are the closest to the vehicle on a daily basis,” Flodin of Bendix says. “Daily checks are important, as well as paying attention to changes in how the brakes are functioning — reduction in torque, leaking air or hot brakes could all be indications of a problem.”

Choosing friction material
Suppliers note that the selection of brake lining for school buses should be based on more than price. Baldwin of Marathon Brake says that many school districts purchase brake lining by competitive tenders with no specifications.

“Even spec’ing the OEM brake lining may not be the most effective method,” Baldwin says. “Axle manufacturers supply axles to school bus manufacturers that may only be fitted with truck brake lining. Such on-highway truck lining is not well suited for the rigors of frequent stopping, which creates high brake temperatures, and many buses are operated in rural roads with lots of contamination.”

Baldwin recommends spec’ing a brake lining that is rated for the gross axle weight rating and designed for high heat applications. Friction materials that are designed for school buses are available; they are quiet and durable, and they maintain consistent braking at all operating temperatures.

Another important factor is flexural strength. “A high flexural strength product,” Baldwin explains, “will not crack as the brake temperatures rise and the shoe flexes as the brake drum expands and contracts with heat and pressures.”

Related Topics: brakes, parts

Thomas McMahon Executive Editor
Comments ( 6 )
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  • Brad Barker

     | about 2 years ago

    There are a few common brake issues associated with drum type air brakes which are easily cured. If you get a report of a popping or banging noise associated with brake application which may or may not include pulling to one side or the other, the problem is most likely one or both of the following. The brake rollers are not rolling as designed but are rather sliding on the S cam during brake application. This usually occurs when a harder than normal brake application takes place and may not be noticed all of the time. The cause of the pulling action takes place as the sliding roller suddenly rolls on the S cam. A secondary cause of this problem is due to rust forming at the radius area of the shoe which contacts the anchor pin causing binding to take place. I have found that most often the air brake shoe assembly on the front axle is affected more than the brake shoe assembly of the rear axle. To solve the issue a full disassembly of the affected brakes needs to take place. (Note: always disassemble both assemblies on each affected axle. Unless wear is detected the S cams do not need to be removed.) Thoroughly inspect the brake rollers, shoe assemblies, anchor pins, anchor pin bushings, return springs and S cam. I like to take an 80 grit flap wheel in an air drill or die grinder and clean up the S cam surface smoothing out any rough spots and removing all rust and dirt. If the anchor pin bushings are not being replaced, polish the bore of these too. If severe flat spots are noticed on the S cam surface the S cam shoud be replaced. Most often these can be cleaned up though. I always use new anchor pins and new brake rollers and roller retainers upon reassembly. The trick to prevent the problem from reoccurring is the application of Anti-Seize compound at all pivoting wear points except on the surface of the brake roller and S cam. Keep these clean. Apply anti-seize to the pin ends of the brake rollers only as well as the half circle cup areas of the brake shoes and

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