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['CMV Parts and Maintenance']
['Brakes']
06/04/2024
Copyright 2026 J. J. Keller & Associate, Inc. For re-use options please contact copyright@jjkeller.com or call 800-558-5011.
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InstituteIn Depth Sub Topics (Level 4)CMV Parts and MaintenanceTransportationFleet OperationsEnglishBrakesAnalysisFocus AreaUSA
Automatic brake adjusters and indicators
['CMV Parts and Maintenance']
- New CMVs equipped with hydraulic, or air brakes systems must meet the automatic brake adjustment systems requirements of the FMVSS applicable to the vehicle at the time of manufacture.
- For new CMVs equipped with an air brake system containing an external automatic adjustment mechanism and an exposed pushrod, the condition of service brake under-adjustment must be displayed by a brake adjustment indicator conforming to the requirements of the FMVSS applicable to the vehicle at the time it was manufactured.
Hydraulic brake systems and air brake systems on new commercial motor vehicles (CMVs) must be equipped with automatic brake adjusters (“slack adjusters”) that automatically adjust as the brake linings and drums wear. Air brake systems must also be equipped with a brake system indicator that shows the condition of the service brake under adjustment. If the CMV was built with automatic slack adjusters, they cannot be removed and replaced with manual slack adjusters (see 393.53).
Adjustment systems:
- Hydraulic brakes systems — Each CMV manufactured on or after October 20, 1993, and equipped with a hydraulic brake system, must meet the automatic brake adjustment system requirements of Federal Motor Vehicle Safety Standard (FMVSS) No. 105 (49 CFR 571.105, S5.1) applicable to the vehicle at the time it was manufactured.
- Air brake systems — Each CMV manufactured on or after October 20, 1994, and equipped with an air brake system must meet the automatic brake adjustment system requirements of FMVSS No. 121 (49 CFR 571.121, S5.1.8 or S5.2.2) applicable to the vehicle at the time it was manufactured.
Brake adjustment indicator:
- Air brake systems — On each CMV manufactured on or after October 20, 1994, and equipped with an air brake system which contains an external automatic adjustment mechanism and an exposed pushrod, the condition of service brake under-adjustment must be displayed by a brake adjustment indicator conforming to the requirements of FMVSS No. 121 (49 CFR 571.121, S5.1.8 or S5.2.2) applicable to the vehicle at the time it was manufactured.
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cmv-parts-and-maintenance
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CMV parts and maintenance
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Who must comply?
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Exemptions
Automatic brake adjusters and indicators
InstituteIn Depth Sub Topics (Level 4)CMV Parts and MaintenanceTransportationFleet OperationsEnglishBrakesAnalysisFocus AreaUSA
['CMV Parts and Maintenance']
- New CMVs equipped with hydraulic, or air brakes systems must meet the automatic brake adjustment systems requirements of the FMVSS applicable to the vehicle at the time of manufacture.
- For new CMVs equipped with an air brake system containing an external automatic adjustment mechanism and an exposed pushrod, the condition of service brake under-adjustment must be displayed by a brake adjustment indicator conforming to the requirements of the FMVSS applicable to the vehicle at the time it was manufactured.
Hydraulic brake systems and air brake systems on new commercial motor vehicles (CMVs) must be equipped with automatic brake adjusters (“slack adjusters”) that automatically adjust as the brake linings and drums wear. Air brake systems must also be equipped with a brake system indicator that shows the condition of the service brake under adjustment. If the CMV was built with automatic slack adjusters, they cannot be removed and replaced with manual slack adjusters (see 393.53).
Adjustment systems:
- Hydraulic brakes systems — Each CMV manufactured on or after October 20, 1993, and equipped with a hydraulic brake system, must meet the automatic brake adjustment system requirements of Federal Motor Vehicle Safety Standard (FMVSS) No. 105 (49 CFR 571.105, S5.1) applicable to the vehicle at the time it was manufactured.
- Air brake systems — Each CMV manufactured on or after October 20, 1994, and equipped with an air brake system must meet the automatic brake adjustment system requirements of FMVSS No. 121 (49 CFR 571.121, S5.1.8 or S5.2.2) applicable to the vehicle at the time it was manufactured.
Brake adjustment indicator:
- Air brake systems — On each CMV manufactured on or after October 20, 1994, and equipped with an air brake system which contains an external automatic adjustment mechanism and an exposed pushrod, the condition of service brake under-adjustment must be displayed by a brake adjustment indicator conforming to the requirements of FMVSS No. 121 (49 CFR 571.121, S5.1.8 or S5.2.2) applicable to the vehicle at the time it was manufactured.
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Copyright 2026 J. J. Keller & Associate, Inc. For re-use options please contact copyright@jjkeller.com or call 800-558-5011.