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

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(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.

Type	Outside diameter	Brake readjustment limit: standard stroke chamber	Brake readjustment limit: long stroke chamber
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.
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)

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).

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).