49 CFR § 393.45 - Brake tubing and hoses; hose assemblies and end fittings.
(a) General construction requirements for tubing and hoses, assemblies, and end fittings. All brake tubing and hoses, brake hose assemblies, and brake hose end fittings must meet the applicable requirements of FMVSS No. 106 (49 CFR 571.106).
(b) Brake tubing and hose installation. Brake tubing and hose must -
(1) Be long and flexible enough to accommodate without damage all normal motions of the parts to which it is attached;
(2) Be secured against chaffing, kinking, or other mechanical damage; and
(3) Be installed in a manner that prevents it from contacting the vehicle's exhaust system or any other source of high temperatures.
(c) Nonmetallic brake tubing. Coiled nonmetallic brake tubing may be used for connections between towed and towing motor vehicles or between the frame of a towed vehicle and the unsprung subframe of an adjustable axle of the motor vehicle if -
(1) The coiled tubing has a straight segment (pigtail) at each end that is at least 51 mm (2 inches) in length and is encased in a spring guard or similar device which prevents the tubing from kinking at the fitting at which it is attached to the vehicle; and
(2) The spring guard or similar device has at least 51 mm (2 inches) of closed coils or similar surface at its interface with the fitting and extends at least 38 mm (1 1/2 inches) into the coiled segment of the tubing from its straight segment.
(d) Brake tubing and hose connections. All connections for air, vacuum, or hydraulic braking systems shall be installed so as to ensure an attachment free of leaks, constrictions or other conditions which would adversely affect the performance of the brake system.
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