§ 393.42 Brakes required on all wheels.

(a) Every commercial motor vehicle shall be equipped with brakes acting on all wheels. This requirement also applies to certain motor vehicles being towed in a driveaway-towaway operation, as follows:
(1) Any motor vehicle towed by means of a tow-bar when another motor vehicle is full-mounted on the towed vehicle; and
(2) Any saddlemount configuration with a fullmount.
(b) Exception. (1) Trucks or truck tractors having three or more axles—
(i) Needand manufactured before July 25, 1980, are not required to have brakes on the front wheels. ifHowever, thethese vehiclevehicles wasmust manufacturedmeet beforethe Julyrequirements 25,of 1980;§ or393.52.
(ii2) ManufacturedMotor betweenvehicles Julybeing 24,towed 1980,in anda Octoberdriveaway-towaway 27,operation 1986,(including mustthe belast retrofittedtruck of triple saddle-mount combinations (see § 393.71(a)(3)) are not required to meethave operative brakes provided the combination of vehicles meets the requirements of this§ section393.52.
(3) withinAny onesemitrailer yearor frompole Februarytrailer 26(laden or unladen) with a gross weight of 1,361 1987kg (3,000 pounds) or less which is subject to this part is not required to be equipped with brakes if the brakeaxle componentsweight haveof beenthe removedtowed vehicle does not exceed 40 percent of the sum of the axle weights of the towing vehicle.
(24) Any motorfull vehicletrailer beingor towedfour-wheel inpole trailer (laden or unladen) with a driveaway-towawaygross operationweight mustof have1,361 operativekg brakes(3,000 aspounds) mayor beless necessarywhich is subject to ensurethis compliancepart is not required to be equipped with thebrakes performanceif requirementsthe sum of §the 393.52.axle Thisweights paragraphof isthe towed vehicle does not applicableexceed to40 anypercent motorof the sum of the axle weights of the towing vehicle.
(5) towedBrakes byare meansnot required on the steering axle of a towthree-baraxle whendolly anywhich otheris vehiclesteered isby fulla co-mounteddriver.
(6) onLoaded suchhousemoving toweddollies, specialized trailers and dollies used to transport industrial furnaces, reactors, and similar motor vehiclevehicles orare anynot required to be equipped with brakes, provided the speed at which the combination of motor vehicles utilizingwill threebe oroperated moredoes saddle-mounts.not exceed 32 km/hour (See20 §mph) 393and brakes on the combination of vehicles are capable of stopping the combination within 12.712 meters (a40 feet) from the speed at which the vehicle is being operated or 32 km/hour (320 mph), whichever is less.)
(37) AnyPortable fullconveyors trailer,manufactured anyprior semitrailer,to or2010 anyand poleused trailerby havingthe aaggregate GVWRindustry ofare 3,000not poundsrequired orto less must be equipped with brakes ifon theall weightwheels provided:
(i) The combination of theportable towedconveyor and towing vehicle restingmeet onthe performance requirement in 49 CFR 393.52;
(ii) The sum of the towingaxle weights of the towed vehicle exceedsdoes not exceed 40 percent of the GVWRsum of the axle weights of the towing vehicle.; and
[Figure(iii) orThe graphicmaximum omitted.speed Seeof the officialportable sourceconveyor and towing vehicle is limited to 45 miles per hour (mph) on two lane roads and 55 mph on freeways.]
[52 FR 2803, Jan. 27, 1987, as amended at 53 FR 49398, Dec. 7, 1988; 54 FR 48617, Nov. 24, 1989; 59 FR 25574, May 17, 1994; 61 FR 1843, Jan. 24, 1996; 70 FR 48049, Aug. 15, 2005; 76 FR 56321, Sept. 13, 2011; 91 FR 7890, Feb. 19, 2026]