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  • Writer's pictureBob



FMCSA regulations have specific requirements for brakes on commercial motor vehicles.


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


(a) General rule. Except as provided in b, c and d o

f this section, all brakes with which a motor vehicle is equipped must be at all times be capable of operating.

Drivers performing a pre/post trip inspection should be well versed in the components of a brake system. If a defect is observed during the inspection the vehicle should be removed from service until repairs have been made.

Enforcement officers determine if a CMV will be allowed to continue on or if repairs will need to be made onsite. A vehicle will be placed out of service if the number of defective brakes is equal to or greater than 20% of the total number of service brakes on the vehicle combination. A brake can be considered defective for reasons including:

•Brakes out of adjustment, ½” beyond the adjustment limit;

•Audible air leak at chamber;

•Defective lining conditions - cracked, missing lining, lining thickness below ¼ inch;

•Contaminated drum by grease, oil or brake fluid;

•Inoperative - pad failing to move, slack adjuster malfunction;

•Missing parts: pushrod, yoke, clevis pin, S-cam;

•Loose and or missing brake chamber

Commercial motor vehicles can be placed out of service for additional brake related issues that do not require a 20% defective rate:

•Brakes applied air pressure loss

•Defective tractor protection valve

•Low air warning device inoperative or does not activate with air reservoir at 55 psi.

•Cracked drum

•Air lines - air leak at other than proper connection, bulge, swelling in line when brake applied.

As always stay safe and do your pre trip inspection before take off.

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