What Brake System Is Used in a Truck?

Most heavy-duty trucks use compressed-air (pneumatic) brake systems as their primary service brakes, typically with S-cam drum or air disc brakes and spring-applied parking brakes; medium-duty trucks may use hydraulic or air-over-hydraulic systems, and electric or hybrid trucks add regenerative braking to the mix. In practice, modern trucks layer several braking technologies—service, parking/emergency, and auxiliary retarders—to meet safety, performance, and regulatory demands.

How the Primary Truck Braking System Works

For tractors and most heavy goods vehicles, the compressed-air brake system is the backbone of stopping power. It uses air reservoirs charged by an engine-driven compressor and managed by valves and controls to apply friction at the wheels reliably, even under heavy loads and repeated stops.

The following points outline the key components and functions in a typical dual-circuit air brake system used on modern trucks:

• Air compressor and governor: pressurize the system and control cut-in/cut-out, typically around 90–125 psi.
• Air dryer and filtration: remove moisture and contaminants to prevent freezing and corrosion.
• Primary and secondary reservoirs: provide redundancy so a failure in one circuit doesn’t eliminate all braking.
• Foot (treadle) valve: modulates air pressure proportional to pedal input for service braking.
• Brake chambers and actuators: convert air pressure into mechanical force at each wheel.
• Foundation brakes: S-cam drum brakes or air disc brakes apply friction to stop the vehicle.
• Slack adjusters (automatic): maintain proper brake shoe or pad-to-drum/disc clearance.
• Relay and quick-release valves: speed up application and release across long wheelbases.
• Spring brake chambers: provide fail-safe parking/emergency braking when air is lost.
• Electronic controls: ABS is standard; many fleets also use EBS and ESC for stability and braking precision.

Together, these components deliver strong, repeatable braking performance with redundancy, ensuring that a leak or component fault does not remove all stopping capability—a core reason air systems dominate heavy trucking.

Types of Brakes Found on Trucks

Beyond the core service system, trucks combine several brake types to cover routine stops, secure parking, long downhill descents, and energy recovery on electrified vehicles. The exact mix depends on vehicle class, region, and duty cycle.

• Service brakes (primary): air drum or air disc. Drums (S-cam) are robust and widely used; air disc brakes offer shorter stopping distances, better fade resistance, and simpler inspections, and are gaining adoption on new tractors and trailers.
• Parking/emergency brakes: spring-applied, air-released brakes that automatically engage if system pressure drops too low, securing the vehicle.
• Auxiliary retarders: engine/compression-release brakes (“Jake brakes”), exhaust brakes, and driveline/hydraulic retarders manage speed on long grades and reduce friction-brake wear.
• Regenerative braking: hybrid and battery-electric trucks recapture kinetic energy via the drive motor; friction brakes remain for high-demand or low-speed stops and as a safety backup.
• Hydraulic and air-over-hydraulic: common on light and some medium-duty trucks (often Classes 3–6), using hydraulic discs/drums; air-over-hydraulic appears on certain vocational or bus applications.

In real-world fleet specs, heavy-duty on-highway tractors nearly always use full air systems, while medium-duty choices vary by payload, cost, and maintenance preferences. Electrification adds regen but does not eliminate the need for robust friction braking.

Trailer Brakes and Coupling

Combination vehicles rely on coordinated tractor–trailer braking. Standardized air lines and electrical connections ensure the trailer brakes apply promptly and proportionally with the tractor’s service and emergency systems.

• Dual air lines: supply (emergency) and service/control lines connect via gladhand couplers.
• Color coding: in North America, red is the emergency/supply line and blue is the service line; in Europe, red is supply and yellow is control.
• Breakaway/emergency function: loss of the supply line triggers trailer spring brakes to apply, stopping a separated or air-depleted trailer.
• ABS/EBS: trailer ABS is standard; electronically controlled braking systems (EBS) are common in Europe for faster, more balanced response, using the ISO 7638 electrical connector for power/diagnostics.
• Brake balance: correct tractor–trailer balance prevents jackknifing and improves stability, especially on low-friction surfaces.

With proper coupling and maintenance, trailer braking integrates seamlessly with the tractor, maintaining legal performance standards and improving safety under emergency maneuvers.

Safety, Standards, and What’s Required

Truck braking is tightly regulated to ensure predictable stopping distances, redundancy, and stability. Requirements vary by market but share core safety principles.

• FMVSS 121 (U.S.) sets performance and equipment rules for air-braked vehicles; ABS has been required on most new tractors and trailers since the late 1990s.
• ESC/ESP: electronic stability control has been mandated on new U.S. truck tractors since model year 2017; similar requirements apply in the EU.
• Driver qualifications: operating air-braked vehicles in the U.S. typically requires a CDL with an air brake endorsement; comparable licensing standards exist globally.
• Inspection regimes: daily pre-trip checks and periodic inspections (e.g., CVSA, MOT, roadworthiness tests) focus on air leaks, brake stroke, lining thickness, and ABS/EBS faults.
• Operating pressures: systems generally run near 100–125 psi; low-pressure warnings and automatic spring brake application protect against loss of braking.

These rules reflect decades of lessons learned: redundant circuits, automatic adjustment, and electronic controls have significantly improved stopping performance and crash avoidance in modern fleets.

Maintenance and Driver Checks

Air brakes are durable but performance hinges on regular inspection and upkeep. Drivers and technicians share responsibility for detecting issues early, before they affect stopping power.

• Daily checks: air leakage tests, pressure build-up time, low-pressure warnings, and parking brake hold tests.
• Visual inspections: lining/pad thickness, drum/disc condition, air lines and gladhands, chamber mounts, and slack adjuster alignment.
• Automatic slack adjusters: verify correct operation; never “adjust to mask” underlying mechanical issues.
• Air system health: drain reservoirs as specified, service air dryers, and track compressor performance.
• Electronics: confirm ABS/EBS indicator status and address fault codes promptly.

Consistent preventive maintenance reduces fade, shortens stopping distances, and extends component life—key to uptime and safety compliance.

What’s Changing in Truck Brakes

Brake technology continues to evolve with safety, decarbonization, and total cost of ownership in mind.

• Air disc brakes: rising adoption on tractors and trailers for improved performance and easier service.
• Regen integration: electric and hybrid trucks blend regenerative and friction braking for efficiency while maintaining air or hydraulic backups.
• EBS and brake-by-wire: faster modulation and smarter diagnostics, especially in Europe and on premium spec vehicles.
• Advanced stability and ADAS: tighter integration of ESC, collision mitigation braking, and adaptive cruise improves control in emergencies.
• Materials and emissions: low-copper/low-dust friction materials and corrosion-resistant hardware extend life and reduce environmental impact.

The direction of travel is clear: more electronics, better modulation, and integration with powertrains to save energy without compromising safety.

Summary

The brake system used in a truck is predominantly a compressed-air (pneumatic) system for heavy-duty applications, complemented by spring-applied parking brakes, ABS/EBS, and often auxiliary retarders. Medium-duty trucks may use hydraulic or air-over-hydraulic systems, and electric/hybrid trucks add regenerative braking. Trailer braking is integrated via dual air lines and standardized electrical connections. Regulations like FMVSS 121 and ESC mandates underpin modern performance, while trends such as air disc brakes and brake-by-wire continue to raise the safety bar.

Which is better ABS or CBS braking system?

If you feel that you are able to apply both brakes at the same time, go for the CBS. However, if your daily commute requires you to apply your bike brakes aggressively from time to time, the Anti-lock Braking System can be a better pick.

What type of braking system do trucks use?

Air brakes
Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers, in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service.

Do trucks use drum or disc brakes?

Systems which primarily use drum brakes while disc brakes are slowly gaining traction in the commercial trucking world drum brakes remain the industry standard and for good.

Which brake is used in a truck?

Drum brakes have historically come standard on commercial trucks and are the most widely used braking system in the truck industry due to their lower cost and ease of manufacturing.