Proper Spring Brake Selection Supports Safer, Dependable Bus Operation

By Keith McComsey, Technical Sales Lead (Wheel-End), Bendix Commercial Vehicle Systems

Keith McComsey

When a brake issue sidelines a bus or motorcoach, the consequences are immediate. Schedules are thrown off. Drivers and dispatchers scramble. Passengers miss connections — and they talk about it. For operators focused on service, safety, and reputation, every delay matters.

That’s why spring brake design — often overlooked — deserves closer attention.

In high-uptime, passenger-focused environments, equipment choices shape performance. And spring brake reliability plays an important role in keeping buses moving.

How Spring Brakes Work — And Fail

Spring brakes perform two critical functions in air-braked vehicles: service braking and parking brake applications. Inside each chamber are two parts — a service side and a parking side. The parking side houses a powerful spring that stays compressed during normal operation. When the parking brake is engaged — or if air pressure is lost — that spring is released, applying the brakes for parking or, in the event of air pressure loss, as a safety redundancy to protect the vehicle and stop.

This dual-function setup is standard across trucks, trailers, and buses. The longevity and operability of the brake rests on the ability of the power spring to maintain its force over time, which is why engineering the spring for maximum durability is crucial. Yet the leading cause of spring brake malfunction is a broken power spring. And motorcoach and transit fleets — where uptime is closely tied to customer experience — face higher stakes when the power spring fails.

The most common cause of failure is internal corrosion. Moisture and contaminants enter the chamber — often through open drain holes designed to vent air when the spring releases — and begin to attack the power spring. Over time, coatings degrade, the spring weakens, and in many cases, will abruptly fail. The broken spring may even puncture the rubber diaphragm, resulting in an air leak.

Even routine practices can accelerate the problem. Washdowns can introduce water and caustic detergents and/or activate deicing agents. Winter road salt and urban grime collect at the wheel-end and break down the spring coating, exposing it to corrosion. And vehicles parked for long periods may collect condensation inside the chamber where it may become trapped and accelerate corrosion.

In many cases, damage goes undetected until failure occurs, taking the vehicle out of service.

Sealed Chambers Can Help

Sealed spring brake chambers are designed to address the main vulnerability of traditional models: exposure to contaminants and the elements. (1)

In transit and motorcoach environments, where vehicles may face frequent washdowns, salted winter roads, or long idle periods, this added protection becomes even more valuable.

Know The Differences

Many spring brake chambers in the market today are labeled as “premium” even if they’re not sealed. And almost all manufacturers emphasize the protective coatings on their power springs, but lab testing shows those coatings only go so far. If the chamber allows external elements inside, even the best coatings can’t prevent long-term damage. The most effective defense is to keep contaminants out entirely — starting with a sealed design that protects the internal components.

When spec’ing spring brakes, it’s worthwhile for motorcoach and transit service fleets to dig deeper to make sure the design aligns with their operating conditions and reliability goals. That includes looking not just at form and function, but at the manufacturing quality, materials, and sealing precision that determine performance and longevity.

Here’s an example: Over time, spring coils can rub against one another during compression — a condition known as coil clash — which gradually erodes protective coatings and weakens the spring. To help prevent this, choose designs with optimized spring geometry and carefully selected shut height to reduce compression stress and preserve consistent braking force over time.

Five Questions To Ask When Spec’ing Spring Brakes:

1. Is the chamber sealed? Look for designs that eliminate open drain holes and block out contaminants.
2. What’s the shut height of the spring? A greater shut height reduces compression stress and preserves force output over time.
3. Does it prevent coil clash? Optimized spring geometry minimizes internal abrasion and protects the power spring coating.
4. Is the brake suited for your fleet environment? Consider exposure to corrosive elements. Don’t overlook temperature swings or humidity, which can increase the risk of condensation inside the chamber.
5. Will it integrate with your maintenance plan? Select components that support longer intervals between inspections or help reduce downtime.

Small Design, Big Impact

Spring brake chambers aren’t top of mind for most passengers. But when they fail, the effects are impossible to ignore — especially in highly visible, passenger-focused fleets.

Spring brakes that resist internal corrosion and minimize mechanical wear offer a practical upgrade that helps extend service life, protect uptime, and keep fleets moving smoothly. And while they may carry a modest upfront premium, their performance advantages can reduce unplanned maintenance and lower total cost of ownership.

In transit and motorcoach fleets, consistency builds confidence — ride by ride, schedule by schedule. That kind of reliability doesn’t come from luck. It comes from the decisions made upstream, starting with the spec.

Keith McComsey is the Technical Sales Lead (Wheel-End) at Bendix Commercial Vehicle Systems. A mechanical engineer by training, McComsey has more than 30 years of experience in the commercial vehicle industry across both OEM and supplier roles. His role at Bendix includes leading efforts in product development, customer solutions, and performance innovation.

Bendix Commercial Vehicle Systems, a member of Knorr-Bremse, develops and supplies leading-edge active safety technologies, energy management solutions, and air brake charging and control systems and components under the Bendix^® brand name for medium- and heavy-duty trucks, tractors, trailers, buses, and other commercial vehicles throughout North America. An industry pioneer, employing more than 3,600 people, Bendix is driven to deliver the best solutions for improved vehicle safety, performance, and overall operating cost. Contact us at 1-800-AIR-BRAKE (1-800-247-2725) or visit bendix.com. Stay connected and informed through Bendix expert podcasts, blog posts, videos, and other resources at knowledge-dock.com. Follow Bendix on X, formerly known as Twitter, at https://x.com/Bendix_CVS. Log on and learn from the Bendix experts at brake-school.com. And to learn more about career opportunities at Bendix, visit bendix.com/careers.

Footnote:

(1) The Bendix® EnduraSure®-Pro™ eliminates drain holes by using a one-way check valve integrated into the dust plug. This design enables the chamber to “breathe,” stabilizing internal pressure while blocking contaminants – helping prevent corrosion before it starts and extending the life of the parking spring. Bendix adds an additional layer of protection on the exterior by e-coating the chamber.