How spring brake design impacts maintenance cycles and performance

How spring brake design impacts maintenance cycles and performance

How do you prevent the corrosion that perpetuates the costly cycle of spring brake replacement?

You probably don’t think much about your spring brakes until one needs to be replaced. And while that might be said for a lot of commercial vehicle parts, spring brakes are critical components of air-braked systems on both tractors and trailers – which means there’s a lot at stake when it comes to protecting their performance, extending their life cycle and making sure you’re equipping the best type for your specific needs.

Spring brakes are responsible for both service and parking brake applications. The service chamber side of the brake is used to slow or stop a vehicle, while the parking side holds the vehicle in place when it’s parked and functions as a fail-safe brake in the event that the brake system loses air pressure. Within that parking side in what’s referred to as the spring brake chamber, there’s a large, powerful spring.

Under normal operating conditions while the vehicle is in motion, this spring is compressed. Once a vehicle is parked, the spring’s tremendous tension is released, providing the braking force that holds the vehicle in place. The longevity and operability of the brake rests on its ability to maintain this force over time, so it’s vital to design this spring for durability. A broken power spring is the leading cause of spring brake malfunction, and its failure makes downtime a certainty.

Replacement time already?

Fleets that find themselves replacing spring brakes ahead of schedule and dealing with unplanned maintenance costs and time in the shop often wonder why the components aren’t meeting product life expectations. There are a few possibilities.

A broken power spring is most often triggered by moisture and contaminants like road salts invading the brake chamber and weakening the power spring.

So how do you prevent the corrosion that perpetuates the costly cycle of spring brake replacement? Start with a look at your spring brake’s design.

A standard spring brake is engineered with drain holes that allow air to escape when the parking brake is released – but these holes can also allow contaminants to enter. Sealed spring brakes are designed to prevent this. The Bendix EnduraSure Pro, for example, eliminates the drain holes and integrates a one-way check valve into the screw-in dust plug. This allows the brake to “breathe” while still keeping out contaminants.

The seal of protection

By protecting the power spring, sealed spring brakes deliver long-lasting value to any fleet, but they make especially good sense for those operating in severe or off-road applications like bulk hauling. Why? Because things like aggregates and dust can also get in through a standard brake’s drain holes, degrading the power spring and increasing the risk of failure.

Fleets that generally keep their equipment for extended periods of time will also benefit from spec’ing a chamber that helps lengthen service intervals. Sealed spring brakes can also add valuable protection to trailers that sit for long periods, since these wheel-ends can be more susceptible to moisture finding its way inside standard spring brakes.

They’re not all the same

If it looks like sealed spring brakes are the solution you need, make sure you shop smart: Not all spring brakes marketed as “premium” are sealed. Keep in mind that while many will tout protective coatings on the power spring itself, that’s not nearly as effective as preventing a corrosive environment from developing in the first place.

Additionally, be sure to ask about other design aspects of the brake: Is it engineered to avoid coil clash, where the coils of the compressed power spring make contact and wear away the protective coating? You can also investigate the power spring’s shut height, which reflects the degree to which the spring is compressed. Over-compression can lead to a rapid decrease in its force output, which reduces the safety margin when parking. The greater the power spring shut height, the less stress there is on the spring, allowing it to better maintain its force output over time.

No spring brake lasts forever – they’re wearable components that will require regular replacement. But knowing what you’re getting when it’s time for new ones can help you get longer service life, lower total cost of ownership, and most importantly, more dependable and safe braking performance.

This story was contributed by Mark Holley of Bendix.

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