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5.1.1 Brake Systems (Part 393 Subpart C)

Brake components include actuators, slack adjusters, linings, pads, drums, and rotors. Components must be constructed, installed, and maintained so that vehicles can be stopped safely and reliably.

Commercial vehicles must also meet relevant service, parking, and emergency brake requirements. Brakes must be operable at all times and brakes must act on all wheels, with some limited exceptions for certain trailers, dollies, and driveaway–towaway operations (49 CFR 393.42 (b)).

Requirements for coupling devices, including requirements for full trailers, saddle mount operations, and for attaching and locating a fifth wheel, are in 49 CFR Sections 393.70 and 393.71.

See 49 CFR 393, Subpart C for full requirements and exceptions related to brake systems.

Antilock Brake Systems (393.55)

Some commercial motor vehicles must have antilock brake systems. Hydraulic brake systems must meet the antilock brake requirements included in 49 CFR 571.105. Air brake systems must meet the antilock brake requirements included in 49 CFR 571.121.

See the applicable regulations mentioned here, and in 49 CFR 393.55, for full antilock brake requirements.

Breakaway and Emergency Braking (393.43)

Every motor vehicle, if used to tow a trailer equipped with brakes, shall be equipped with a means of providing that in the case of a breakaway of the trailer, the service brakes on the towing vehicle will be capable of stopping the towing vehicle. Trucks or truck tractors with air brakes that are towing other vehicles with air brakes must have both manual and automatic means of activating the emergency features of the trailer brakes.

See 49 CFR 393.43 for full regulations on breakaway and emergency braking requirements and exceptions, including for driveaway–towaway operations.

Tubing and Hoses (393.45)

All brake tubing and hoses, brake hose assemblies, and brake hose end fittings such as gladhand connectors must meet the applicable requirements of FMVSS No 106 (49 CFR 571.106).

Brake tubing and hose installation must:

  • Have length and flexibility that allow parts to move normally, without damage, where the hose is attached;
  • Be protected against chafing, kinking, and mechanical damage; and
  • Not contact exhaust pipes and other sources of high temperature.

See 49 CFR 393.45 for complete tubing and hose requirements.

Warning Devices (393.51)

In general, buses, trucks, and truck tractors must have a signal that warns their driver when the vehicle’s service brake system fails. This warning signal applies to hydraulic brake systems, air brake systems, vacuum brake systems, and hydraulic brakes applied or assisted by air or vacuum.

See 49 CFR 393.51 for full requirements on warning devices and exceptions for certain commercial vehicles.

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