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Understanding the Brake System Configuration
Fontaine lowbed trailers are widely used in heavy haul applications due to their robust frame design and low deck height. These trailers typically rely on air brake systems that include both service brakes (activated during normal braking) and parking brakes (spring-applied, air-released). However, some Fontaine lowbeds—especially older or custom-ordered units—may lack spring brake chambers entirely, leading to confusion when the trailer fails to hold position after disconnection.
In a standard setup, parking brakes are applied by spring force when air pressure is removed. This is achieved using dual-chamber spring brake actuators, commonly referred to as spring cans. If a trailer is equipped only with single-diaphragm service chambers (Type 30), it will not have a true parking brake function.
Symptoms and Initial Observations
Operators encountering this issue often report:
Confirming Brake Chamber Type
To verify the presence or absence of parking brakes:
Historical Context and Regulatory Shifts
In earlier decades, it was not uncommon for lowbed trailers to be ordered without spring brakes. This was sometimes intentional, especially for trailers that needed to be moved by equipment without air systems, such as dozers or winches. However, modern Department of Transportation (DOT) regulations generally require spring brakes on all axles for safety reasons.
Some trailers were built during a transitional period when ABS systems were introduced but spring brakes were not yet mandated. As a result, it is possible to find trailers with ABS wiring but no spring brake chambers.
Potential Causes and Contributing Factors
Some operators have fabricated extension air lines with gladhands on both ends to recharge trailer tanks before coupling. Others have added spring brake kits to older trailers to comply with current safety standards. In one case, a mechanic retrofitted a 2008 Mack tractor with additional spring chambers after discovering that only one drive axle had parking brakes—a configuration more common in trucks from the 1960s and 70s.
Conclusion
The absence of parking brakes on a Fontaine lowbed trailer is often a result of original configuration choices or later modifications. While service brakes may function correctly, the lack of spring-applied brakes poses a serious safety risk during disconnection or air loss. A thorough inspection of brake chamber types, air system integrity, and relay valve function is essential. Retrofitting spring brake chambers is strongly recommended to meet modern safety expectations and regulatory compliance.
Fontaine lowbed trailers are widely used in heavy haul applications due to their robust frame design and low deck height. These trailers typically rely on air brake systems that include both service brakes (activated during normal braking) and parking brakes (spring-applied, air-released). However, some Fontaine lowbeds—especially older or custom-ordered units—may lack spring brake chambers entirely, leading to confusion when the trailer fails to hold position after disconnection.
In a standard setup, parking brakes are applied by spring force when air pressure is removed. This is achieved using dual-chamber spring brake actuators, commonly referred to as spring cans. If a trailer is equipped only with single-diaphragm service chambers (Type 30), it will not have a true parking brake function.
Symptoms and Initial Observations
Operators encountering this issue often report:
- Service brakes function normally when connected to a tractor
- Parking brake valve momentarily applies brakes, then releases
- Trailer rolls freely when disconnected from the tractor
- No obvious air leaks or hissing sounds
- ABS wiring may be disconnected or missing
Confirming Brake Chamber Type
To verify the presence or absence of parking brakes:
- Inspect the brake chambers on each axle
- Spring brake chambers are larger and have a piggyback design (two chambers stacked)
- Service-only chambers are single-diaphragm and lack the spring housing
Historical Context and Regulatory Shifts
In earlier decades, it was not uncommon for lowbed trailers to be ordered without spring brakes. This was sometimes intentional, especially for trailers that needed to be moved by equipment without air systems, such as dozers or winches. However, modern Department of Transportation (DOT) regulations generally require spring brakes on all axles for safety reasons.
Some trailers were built during a transitional period when ABS systems were introduced but spring brakes were not yet mandated. As a result, it is possible to find trailers with ABS wiring but no spring brake chambers.
Potential Causes and Contributing Factors
- Removed or bypassed spring chambers: Previous owners may have replaced dual chambers with single ones for specific operational needs
- Relay valve malfunction: If the trailer was originally equipped with spring brakes, a faulty relay valve or plumbing error could prevent proper application
- Air tank leakage: If the trailer’s air tanks cannot hold pressure, the system may fail to maintain brake application
- Contamination in air lines: Mud dauber nests, leaf debris, or rust can block airflow, especially in trailers that sit unused for long periods
- Drain trailer air tanks and observe whether brakes apply—if not, spring brakes are likely absent
- Check airflow through gladhands and relay valve ports using compressed air
- Inspect for mud dauber nests or other obstructions in air lines
- Install gladhand screens to prevent future contamination
- Consider retrofitting spring brake chambers if the trailer is to be used in modern fleets or on public roads
Some operators have fabricated extension air lines with gladhands on both ends to recharge trailer tanks before coupling. Others have added spring brake kits to older trailers to comply with current safety standards. In one case, a mechanic retrofitted a 2008 Mack tractor with additional spring chambers after discovering that only one drive axle had parking brakes—a configuration more common in trucks from the 1960s and 70s.
Conclusion
The absence of parking brakes on a Fontaine lowbed trailer is often a result of original configuration choices or later modifications. While service brakes may function correctly, the lack of spring-applied brakes poses a serious safety risk during disconnection or air loss. A thorough inspection of brake chamber types, air system integrity, and relay valve function is essential. Retrofitting spring brake chambers is strongly recommended to meet modern safety expectations and regulatory compliance.
