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Historical textIn force on Oct. 1, 2005Source: annual CFR editions 2005–2006

§ 393.40 Required brake systems.

Wording in the annual edition revised as of Oct. 1, 2005, superseded by the 2007 annual edition.

govinfo, 2005 edition ↗
Before Jan. 1, 2017 the record is one snapshot per annual CFR edition, revised as of October 1. This is the 2005 edition's wording. An amendment that took effect between Oct. 1, 2005 and Oct. 1, 2005 would not appear until the next edition, so check the citations below and the Federal Register for exact effective dates.
What changedOct. 1, 1996 wording → Oct. 1, 2005 wording+555 added−200 removedHide

(a) GeneralEach commercial motor vehicle must have brakes adequate to stop and hold the vehicle or combination of motor vehicles. AEach buscommercial motor vehicle must meet the applicable service, truckparking, truckand tractor,emergency brake system requirements provided in this section.
(b) Service brakes. (1) Hydraulic brake systems. Motor vehicles equipped with hydraulic brake systems and manufactured on or after September 2, 1983, must, at a combinationminimum, have a service brake system that meets the requirements of motorFMVSS No. 105 in effect on the date of manufacture. Motor vehicles which were not subject to FMVSS No. 105 on the date of manufacture must have brakesa adequateservice tobrake controlsystem that meets the movementapplicable requirements of §§ 393.42, 393.48, 393.49, 393.51, and to393.52 stopof this subpart.
(2) Air brake systems. Buses, trucks and holdtruck-tractors equipped with air brake systems and manufactured on or after March 1, the1975, vehicleand trailers manufactured on or combinationafter January 1, 1975, must, at a minimum, have a service brake system that meets the requirements of FMVSS No. 121 in effect on the date of manufacture. Motor vehicles which were not subject to FMVSS No. 121 on the date of manufacture must have a service brake system that meets the applicable requirements of §§ 393.42, 393.48, 393.49, 393.51, and 393.52 of this subpart.
(b3) SpecificVacuum systemsbrake requiredsystems. (1)Motor Avehicles busequipped with vacuum brake systems must have a service brake system that meets the applicable requirements of §§ 393.42, truck393.48, truck393.49, tractor393.51, orand combination393.52 of motorthis subpart.
(4) Electric brake systems. Motor vehicles equipped with electric brake systems must have—
(i) Aa service brake system that conformsmeets to the applicable requirements of §§ 393.42, 393.52;48, 393.49 and 393.52 of this subpart.
(iic) AParking brakes. Each commercial motor vehicle must be equipped with a parking brake system that conformsmeets to the applicable requirements of §  393.41.
(2d) AEmergency busbrakes—partial failure of service brakes.
(1) Hydraulic brake systems. Motor vehicles manufactured on or after September 2, truck1983, truckand tractorequipped with a split service brake system must, orat a combinationminimum, meet the partial failure requirements of motorFMVSS vehiclesNo. 105 in effect on the date of manufacture.
(2) Air brake systems. Buses, trucks and truck tractors manufactured on or after JulyMarch 1, 19731975, and trailers manufactured on or after January 1, 1975, must havebe equipped with an emergency brake system thatwhich, conformsat a minumum, meets the requirements of FMVSS No. 121 in effect on the date of manufacture.
(3) Vehicles not subject to FMVSS Nos. 105 and 121 on the date of manufacture. Buses, trucks and truck tractors not subject to FMVSS Nos. 105 or 121 on the date of manufacture must meet the requirements of §  393.5240(be). andTrailers consistsnot subject to FMVSS No. 121 at the time of either—manufacture must meet the requirements of § 393.43.
(ie) Emergency brakes, vehicles manufactured on or after July 1, 1973. (1) A bus, truck, truck tractor, or a combination of motor vehicles manufactured on or after July 1, 1973, and not covered under paragraphs (d)(1) or (d)(2) of this section, must have an emergency brake system which consists of emergency features of the service brake system; or
(ii) Aan emergency system separate from the service brake system. The emergency brake system must meet the applicable requirements of §§ 393.43 and 393.52.
(2) A control by which the driver applies the emergency brake system must be located so that the driver can readily operate it whenfrom he/shethe isnormal properlyseating position while restrained by any seat beltbelts assemblywith providedwhich forthe his/hervehicle useis equipped. The control for applying the emergency brake systemcontrol may be combined with either the control for applying the service brake systemcontrol or the control for applying the parking brake systemcontrol. However, all three controls may not be combined.
(cf) Interconnected systems. (1) If the brake systems specifiedrequired inby paragraph § 393.40(ba) of this section are interconnected in any way, they must be designed, constructed, and maintained so that, uponin the event of a failure of any part of the operating mechanism of one or more of the systems (except the service brake actuation pedal or valve)—
(i), Thethe motor vehicle will have operative brakes; and
(ii), Infor thevehicles case of a vehicle manufactured on or after July 1, 1973, thebe vehicle will have operative brakes capable of performingmeeting asthe specifiedrequirements inof §  393.52(b).
(2) A motor vehicle to which the emergency brake system requirements of FederalFMVSS Motor Vehicle Safety Standard No. 105 (§ 571S5.1051.2), dealing with partial failure of thisthe title)service brake, applied at the time of its manufacture conformsmeets to the requirements of paragraph § 393.40(cf)(1) ofif thisthe sectionmotor if—
(i)vehicle It is maintained in conformity with theFMVSS emergency brake requirements of Standard No. 105 inand effect on the datemotor ofvehicle its manufacture; and
(ii) It is capable of performingmeeting asthe specifiedrequirements inof §  393.52(b), except uponin the case of a structural failure of itsthe brake master cylinder body or effectiveness indicator body.
(3) A bus conformsis considered to meet the requirements of paragraph § 393.40(cf)(1) of this section if it meets the requirements of §  393.44 and is capable of performing as specified in §  393.52(b).
[3670 FR 2029748048, OctAug. 2015, 1971, as amended at 37 FR 5251, Mar. 11, 19722005]

49 CFR § 393.40 — Required brake systems.. Text in force on October 1, 2005. This wording effective October 1, 2005 to October 1, 2007. Source: govinfo, 2005 edition, https://www.govinfo.gov/app/details/CFR-2005-title49-vol5/CFR-2005-title49-vol5-sec393-40. Retrieved from FMCSR.com, https://fmcsr.com/reg/393.40?asof=2005-10-01, on October 26, 2026. Unofficial compilation; verify against the official source.

(a) Each commercial motor vehicle must have brakes adequate to stop and hold the vehicle or combination of motor vehicles. Each commercial motor vehicle must meet the applicable service, parking, and emergency brake system requirements provided in this section.

(b) Service brakes. (1) Hydraulic brake systems. Motor vehicles equipped with hydraulic brake systems and manufactured on or after September 2, 1983, must, at a minimum, have a service brake system that meets the requirements of FMVSS No. 105 in effect on the date of manufacture. Motor vehicles which were not subject to FMVSS No. 105 on the date of manufacture must have a service brake system that meets the applicable requirements of §§ 393.42, 393.48, 393.49, 393.51, and 393.52 of this subpart.

(2) Air brake systems. Buses, trucks and truck-tractors equipped with air brake systems and manufactured on or after March 1, 1975, and trailers manufactured on or after January 1, 1975, must, at a minimum, have a service brake system that meets the requirements of FMVSS No. 121 in effect on the date of manufacture. Motor vehicles which were not subject to FMVSS No. 121 on the date of manufacture must have a service brake system that meets the applicable requirements of §§ 393.42, 393.48, 393.49, 393.51, and 393.52 of this subpart.

(3) Vacuum brake systems. Motor vehicles equipped with vacuum brake systems must have a service brake system that meets the applicable requirements of §§ 393.42, 393.48, 393.49, 393.51, and 393.52 of this subpart.

(4) Electric brake systems. Motor vehicles equipped with electric brake systems must have a service brake system that meets the applicable requirements of §§ 393.42, 393.48, 393.49 and 393.52 of this subpart.

(c) Parking brakes. Each commercial motor vehicle must be equipped with a parking brake system that meets the applicable requirements of § 393.41.

(d) Emergency brakes—partial failure of service brakes.

(1) Hydraulic brake systems. Motor vehicles manufactured on or after September 2, 1983, and equipped with a split service brake system must, at a minimum, meet the partial failure requirements of FMVSS No. 105 in effect on the date of manufacture.

(2) Air brake systems. Buses, trucks and truck tractors manufactured on or after March 1, 1975, and trailers manufactured on or after January 1, 1975, must be equipped with an emergency brake system which, at a minumum, meets the requirements of FMVSS No. 121 in effect on the date of manufacture.

(3) Vehicles not subject to FMVSS Nos. 105 and 121 on the date of manufacture. Buses, trucks and truck tractors not subject to FMVSS Nos. 105 or 121 on the date of manufacture must meet the requirements of § 393.40(e). Trailers not subject to FMVSS No. 121 at the time of manufacture must meet the requirements of § 393.43.

(e) Emergency brakes, vehicles manufactured on or after July 1, 1973. (1) A bus, truck, truck tractor, or a combination of motor vehicles manufactured on or after July 1, 1973, and not covered under paragraphs (d)(1) or (d)(2) of this section, must have an emergency brake system which consists of emergency features of the service brake system or an emergency system separate from the service brake system. The emergency brake system must meet the applicable requirements of §§ 393.43 and 393.52.

(2) A control by which the driver applies the emergency brake system must be located so that the driver can operate it from the normal seating position while restrained by any seat belts with which the vehicle is equipped. The emergency brake control may be combined with either the service brake control or the parking brake control. However, all three controls may not be combined.

(f) Interconnected systems. (1) If the brake systems required by § 393.40(a) are interconnected in any way, they must be designed, constructed, and maintained so that in the event of a failure of any part of the operating mechanism of one or more of the systems (except the service brake actuation pedal or valve), the motor vehicle will have operative brakes and, for vehicles manufactured on or after July 1, 1973, be capable of meeting the requirements of § 393.52(b).

(2) A motor vehicle to which the requirements of FMVSS No. 105 (S5.1.2), dealing with partial failure of the service brake, applied at the time of manufacture meets the requirements of § 393.40(f)(1) if the motor vehicle is maintained in conformity with FMVSS No. 105 and the motor vehicle is capable of meeting the requirements of § 393.52(b), except in the case of a structural failure of the brake master cylinder body.

(3) A bus is considered to meet the requirements of § 393.40(f)(1) if it meets the requirements of § 393.44 and § 393.52(b).

[70 FR 48048, Aug. 15, 2005]

Amendment history

4 distinct wordings on file since Oct. 1, 1996
  1. Oct. 1, 2009 → presentannual editions 2009–2016diff vs. previous
    [70 FR 48048, Aug. 15, 2005, as amended at 72 FR 9870, Mar. 6, 2007]
  2. Oct. 1, 2007 → Oct. 1, 2009annual editions 2007–2008diff vs. previous
    [70 FR 48048, Aug. 15, 2005, as amended at 72 FR 9870, Mar. 6, 2007]
  3. Oct. 1, 2005 → Oct. 1, 2007annual editions 2005–2006diff vs. previousviewing
    [70 FR 48048, Aug. 15, 2005]
  4. Oct. 1, 1996 → Oct. 1, 2005annual editions 1996–2004
    [36 FR 20297, Oct. 20, 1971, as amended at 37 FR 5251, Mar. 11, 1972]

A new entry appears whenever the regulatory words change between government snapshots. Day-precise from the eCFR (2017 onward); before that, one snapshot per annual CFR edition (revised as of October 1). Bracketed citations are the Federal Register history printed with the section.