政策法规现行有效美国跨境陆运

§ 393.47 Brake actuators, slack adjusters, linings/pads and drums/rotors.

效力	法规类型	发布日期	生效日期	发文机构
现行有效	部门规章	2026-02-19	2026-03-23	Code of Federal Regulations (CFR) - Transportation (Title 49)

发布02-19

生效03-23

摘要总结AI 辅助解读

本法规为美国联邦机动车安全标准（FMVSS）第393.47条，规定了商用车辆制动执行器、间隙调整臂、衬片/刹车片及鼓/盘的技术要求。核心内容包括：同一轴两端制动室尺寸与间隙调整臂有效长度必须一致；明确了转向轴与非转向轴在气刹和液刹下的最小衬片厚度阈值（如气刹转向轴连续衬片不小于4.8mm）；详细列出了Clamp、Bendix DD-3、螺栓式及Rotochamber型制动室的推杆行程重新调整限值表格；规定楔式制动衬片标记移动不得超过1.6mm。该条款直接影响跨境陆运车辆的合规检查与日常维护标准。

(a) General requirements. Brake components must be constructed, installed and maintained to prevent excessive fading and grabbing. The means of attachment and physical characteristics must provide for safe and reliable stopping of the commercial motor vehicle.
(b) Brake chambers. The service brake chambers and spring brake chambers on each end of an axle must be the same size.
(c) Slack adjusters. The effective length of the slack adjuster on each end of an axle must be the same.
(d) Linings and pads. The thickness of the brake linings or pads shall meet the applicable requirements of this paragraph—

- (1) Steering axle brakes. The brake lining/pad thickness on the steering axle of a truck, truck-tractor or bus shall not be less than 4.8 mm ( 3/16 inch) at the shoe center for a shoe with a continuous strip of lining; less than 6.4 mm ( 1/4 inch) at the shoe center for a shoe with two pads; or worn to the wear indicator if the lining is so marked, for air drum brakes. The steering axle brake lining/pad thickness shall not be less than 3.2 mm ( 1/8 inch) for air disc brakes, or 1.6 mm ( 1/16 inch) or less for hydraulic disc, drum and electric brakes.

- (2) Non-steering axle brakes. An air braked commercial motor vehicle shall not be operated with brake lining/pad thickness less than 6.4 mm ( 1/4 inch) or to the wear indicator if the lining is so marked (measured at the shoe center for drum brakes); or less than 3.2 mm ( 1/8 inch) for disc brakes. Hydraulic or electric braked commercial motor vehicles shall not be operated with a lining/pad thickness less than 1.6 mm ( 1/16 inch) (measured at the shoe center) for disc or drum brakes.

(e) Clamp, Bendix DD-3, bolt-type, and rotochamber brake actuator readjustment limits. (1) The pushrod stroke must not be greater than the values specified in the following tables:

Clamp-Type Brake Chambers Type Outside diameter Brake readjustment limit: standard stroke chamber Brake readjustment limit: long stroke chamber 6 4 1/2 in. (114 mm) 1 1/4 in. (31.8 mm) 9 5 1/4 in. (133 mm) 1 3/8 in. (34.9 mm) 12 5 11/16 in. (145 mm) 1 3/8 in. (34.9 mm) 1 3/4 in. (44.5 mm). 16 6 3/8 in. (162 mm) 1 3/4 in. (44.5 mm) 2 in. (50.8 mm). 20 6 25/32 in. (172 mm) 1 3/4 in. (44.5 mm) 2 in. (50.8 mm). 2 1/2 in. (63.5 mm). 1 24 7 7/32 in. (184 mm) 1 3/4 in. (44.5 mm) 2 in. (50.8 mm). 2 1/2 in. (63.5 mm). 2 30 8 3/32 in. (206 mm) 2 in. (50.8 mm) 2 1/2 in. (63.5 mm). 36 9 in. (229 mm) 2 1/2 in. (63.5 mm) 1 For type 20 chambers with a 3-inch (76 mm) rated stroke. 2 For type 24 chambers with a 3-inch (76 mm) rated stroke.

Bendix DD-3 Brake Chambers Type Outside diameter Brake readjustment limit 30 8 1/8 in. (206 mm) 2 1/4 in. (57.2 mm).

Bolt-Type Brake Chambers Type Outside diameter Brake readjustment limit A 6 15/16 in. (176 mm) 1 3/8 in. (34.9 mm). B 9 3/16 in. (234 mm) 1 3/4 in. (44.5 mm). C 8 1/16 in. (205 mm) 1 3/4 in. (44.5 mm). D 5 1/4 in. (133 mm) 1 1/4 in. (31.8 mm). E 6 3/16 in. (157 mm) 1 3/8 in. (34.9 mm). F 11 in. (279 mm) 2 1/4 in. (57.2 mm). G 9 7/8 in. (251 mm) 2 in. (50.8 mm).

Rotochamber-Type Brake Chambers Type Outside diameter Brake readjustment limit 9 4 9/32 in. (109 mm) 1 1/2 in. (38.1 mm). 12 4 13/16 in. (122 mm) 1 1/2 in. (38.1 mm). 16 5 13/32 in. (138 mm) 2 in. (50.8 mm). 20 5 15/16 in. (151 mm) 2 in. (50.8 mm). 24 6 13/32 in. (163 mm) 2 in. (50.8 mm). 30 7 1/16 in. (180 mm) 2 1/4 in. (57.2 mm). 36 7 5/8 in. (194 mm) 2 3/4 in. (69.9 mm). 50 8 7/8 in. (226 mm) 3 in. (76.2 mm).

- (2) For actuator types not listed in these tables, the pushrod stroke must not be greater than 80 percent of the rated stroke marked on the actuator by the actuator manufacturer, or greater than the readjustment limit marked on the actuator by the actuator manufacturer.

(f) Wedge brake adjustment. The movement of the scribe mark on the lining shall not exceed 1.6 mm ( 1/16 inch).
(g) Drums and rotors. The thickness of the drums or rotors shall not be less than the limits established by the brake drum or rotor manufacturer.

[70 FR 48051, Aug. 15, 2005, as amended at 77 FR 46638, Aug. 6, 2012; 86 FR 57076, Oct. 14, 2021]