Statutes, codes, and regulations
Maryland Administrative code
Title 11 - DEPARTMENT OF TRANSPORTATIONSubtitle 22 - MOTOR VEHICLE ADMINISTRATION-PREVENTIVE MAINTENANCE PROGRAM
Chapter 11.22.04 - Preventive Maintenance Standards for Freight Trailers and Freight Semitrailers
Section 11.22.04.05 - Brake System - Air

Md. Code Regs. 11.22.04.05

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Current through Register Vol. 51, No. 26, December 27, 2024
Section 11.22.04.05 - Brake System - Air
A. Air Leakage. Inspection for leakage shall be conducted with a fully charged system and brakes fully applied.

Procedures:Reject Vehicle If:
(1) Single Vehicle. With a fully charged system, stop engine and observe pressure drop in 1 minute.(1) Air pressure drop is greater than 3 psi in 1 minute.

B. Air Reservoir and Valves.

Procedures:Reject Vehicle If:
(1) Air Reservoir. With system fully charged, open primary (wet) tank drain valve and observe operation of check valve. Then open drain valve on secondary (dry) tank.(1) Check valve does not close and air is retained in the secondary (dry) tank or tanks.
(2) Contamination. Observe any oil or water expelled from all tanks.(2) Any deposits of oil or water cannot be expelled.
(3) Quick Release Valves. Apply and release air in the system.(3) Air is not quickly exhausted through exhaust port when brakes are released.
(4) Relay Valves. Apply and release brakes and observe function of proper brake chambers.(4) Air is not directed to proper brake chamber when brakes are applied or air is not quickly exhausted when brakes are released.

C. Parking and Emergency Brake Application. Vehicles with original equipment air-operated parking brakes are permissible. There are different systems designed for automatic or manual operation of the system as the design allows (check automatic application of brakes when air tanks are being drained).

Procedures:Reject Vehicle If:
(1) Using park brake control valve, release air pressure from brakes.(1) Push rods are extended and vehicle can be moved.
(2) Observe if mechanism releases brakes when control valve is operated.(2) Brakes do not fully release.

D. Gladhands and Air System.

Procedures:Reject Vehicle If:
(1) Visually inspect gladhands for condition and mounting.(1) Gladhands are damaged, have damaged seals, or are insecurely mounted.
(2) Visually inspect lines and hoses for:
(a) Type.
(b) Condition.
(c) Mounting.		(2)
(a) Not an approved type.
(b) Broken, cracked, chafed, abraded, or kinked.
(c) Insecurely mounted or contacting the exhaust system or any moving part.
(3) Inspect air tanks for:
(a) Presence and connection.
(b) Condition.
(c) Leaks.
(d) Mounting.		(3)
(a) Tank is missing or not connected.
(b) Tank is cracked, damaged, or field repaired.
(c) Tank or connections leak.
(d) Tank, mounting brackets, or springs are missing, broken, cracked, or loose.
(4) Inspect drain cocks and moisture ejectors (if equipped) for:
(a) Presence and condition.
(b) Leaks.		(4)
(a) Drain cock is missing, broken, damaged, or is inoperable.
(b) Drain cock or moisture ejector leaks air.

E. Brake Mechanical Components. Do not attempt to dismantle a double diaphragm spring brake unit while it is on the vehicle. Utilize a safety cage and remove the entire unit from the vehicle. Replace with a new or rebuilt assembly. When rebuilding or overhauling a brake chamber, strict adherence to manufacturer's procedures is required. Inspect brake chamber for:

Procedures:Reject Vehicle If:
(1) Function.(1) Brake chamber fails to function as designed.
(2) Leaks.(2) Brake chamber leaks or diaphragm is damaged.
(3) Damage.(3) Brake chamber is damaged so as to affect operation.
(4) Mounting.(4) Brake chamber or mounting hardware is broken, loose, damaged, or bolts are missing.
(5) Push rods.(5) Push rod is broken, bent, or misaligned with slack adjuster.
(6) Clevis yokes.(6) Clevis yoke is broken, cracked, or worn.
(7) Clevis pins.(7) Clevis pin is missing, worn, or cotter pin is missing or an improper substitute is used.
(8) Push rod clevis pin hole setting.(8) Slack adjuster effective length is not the same on all wheels.
(9) Slack adjuster.(9) Slack adjuster is inoperative, broken, bent, extremely worn, or does not function as designed.
(10) Slack adjuster nut self-locking sleeve.(10) Adjusting nut self-locking sleeve does not function.

F. Slack Adjuster (Push Rod) Travel. With the assistance of a second party, apply 85 psi in system and note rod travel.

Procedures:Reject Vehicle If:
(1) With brakes released, inspect angle of push rod and slack adjuster arm.(1) Push rod and slack adjuster arm is less than 90 degrees when brakes are released.
(2) Measure push rod travel from limits in fully released to fully applied positions.(2) Push rod travel exceeds limits in Table 1.

TABLE 1 S-CAM BRAKES-PUSH ROD TRAVEL LIMITS (Dimensions in Inches)

TypeEffective
Area
(Sq. In.)		Outside
Diameter*
(Inches)		Maximum
Stroke
(Inches)
BOLT TYPE BRAKE CHAMBER DATA
A126-15/161-3/8
B249-3/161-3/4
C168-1/161-3/4
D65-1/41-1/4
E96-3/161-3/8
F36112-1/4
G309-7/82
ROTOCHAMBER DATA
994-9/321-1/2
12124-13/161-1/2
16165-13/322
20205-15/162
24246-13/322
30307-1/162-1/4
36367-5/82-3/4
50508-7/83
CLAMP TYPE BRAKE CHAMBER DATA
664-1/21-1/4
995-1/41-3/8
12125-11/161-3/8
16166-3/81-3/4
20206-25/321-3/4
24247-7/321-3/4**
30308-3/322
363692-1/4
*Dimensions listed do not include cap screw head projections for rotochambers and bolt clamp projections for clamp type brake chambers.
**2 inches for long stroke design.
BENDIX WESTINGHOUSE
DD22
DD32

G. Wedge Brake. With the assistance of a second party, make a full brake application.

Procedures:Reject Vehicle If:
(1) Measure total shoe movement from fully released to fully applied position.(1) Brake shoe movement on wedge brakes exceeds 1/16 inch.

H. Brake Camshafts.

Procedures:Reject Vehicle If:
(1) Inspect operation of brakes.(1) Brake camshaft condition renders any brake inoperable.
(2) Inspect travel of brake cams.(2) Any cam is on end or turns over when brakes are applied.
(3) Inspect for camshaft and bushing wear.(3) There is more than 1/8 inch wear between camshaft and bushings.

I. Brake Linings-Air Brakes. Visually inspect brake shoes. If shoes cannot be seen, removal of the lower portion of the dust cover is required.

Procedures:Reject Vehicle If:
(1) Inspect for presence and condition of lining.(1) Any lining is missing, cracked, broken, or not securely attached to the brake shoe.
(2) Measure thickness at center of shoe. It may be necessary to back off slack adjusters to make an accurate measurement.(2) Brake lining thickness is worn to 1/4 inch or less at center of shoe.
(3) Visually inspect for contamination.(3) Lining is contaminated with oil or grease.

J. Brake Drums-Air Brakes.

Procedures:Reject Vehicle If:
(1) Visually inspect for damage and cracks.(1) Any drum contains cracks in the friction surface which extend to the outer edge of the bore or any drum contains any external cracks.
(2) Removal of any wheel and brake drum is only required when a rejection occurs under §J(1). When any wheel and brake drum is removed, perform the inspection specified in §J(3).(2) (Rejection not applicable in this step)
(3) Measure inside diameter of drum for wear and remachining.(3) Any combination of wear and remachining exceeds the brake drum manufacturer's limits. If a limit is not available, the maximum combination of wear and remachining may not exceed 0.090 inch greater than the original inside diameter of the drum if the original diameter of the drum is 11 inches or less. For drums greater than 11 inches inside diameter, the maximum wear and remachining may not exceed 0.120 inch greater than the original inside diameter.

K. Disc Brakes-Air.

Procedures:Reject Vehicle If:
(1) Inspect all calipers and rotor (disc) surfaces for oil or grease contamination.(1) Oil or grease is evident on accessible surfaces of any caliper or rotor (disc).
(2) If brake linings are visible, visually inspect thickness of lining.(2) Brake lining thickness appears to be 1/8 inch or less.
(3) If rotors (discs) are visible, visually inspect for cracks or damage.(3) Any rotor is cracked or damaged.
(4) Removal of all wheels on an axle is only required when a rejection occurs under §K(2). Otherwise remove only the wheel where the defect is suspected. When wheels are removed, perform the inspections specified in §K(5)-(8).(4) (Rejection not applicable in this step)
(5) Bonded Linings.
(a) Measure thickness of lining at thinnest point.
(b) Inspect lining condition.		(5)
(a) Thinnest point of remaining lining is 1/8 inch or less.
(b) Bonded lining is broken, cracked, loose, missing, wear is extremely uneven, or lining is contaminated with oil, grease, or brake fluid.
(6) Riveted Lining.
(a) Measure thickness of lining at thinnest point above rivet head.
(b) Inspect lining condition.		(6)
(a) Thinnest point of remaining lining above a rivet head is 1/8 inch or less.
(b) Lining or rivet is broken, cracked, loose, missing, wear is extremely uneven, or lining is contaminated with oil, grease, or brake fluid.
(7) Calipers. Visually inspect for damage and cracks.(7) Caliper is leaking, fails to operate, or piston is seized, or anti-vibration springs are loose or missing.
(8) Rotors (Discs).
(a) Visually inspect for damage and cracks.
(b) Measure thickness of rotor for wear and remachining.		(8)
(a) Any rotor is broken, cracked into the hub, or friction surface cracks extend to the periphery of the rotor.
(b) Any combination of wear and remachining reduces the thickness of the rotor to less than the minimum thickness established by the manufacturer or that stamped on the rotor.

L. Brakes-Electric.

Procedures:Reject Vehicle If:
(1) Inspect brakes for operation.(1) Brakes do not function when electrical current is applied to the system.
(2) Inspect for broken, loose, or corroded terminals and connections.(2) Terminals or connections are broken, loose, or corroded.
(3) Inspect wiring for brakes, worn or frayed insulation, and proper mounting.(3) Wire is broken or insulation is worn or frayed to expose bare wire, or wiring is not supported to prevent rubbing, chafing, or contact with moving vehicle parts.

M. Break Away (Emergency Brake).

Procedures:Reject Vehicle If:
(1) Disconnect brake power from vehicle and observe brake emergency operation.(1) Emergency brakes do not automatically apply and remain applied for at least 15 minutes when brake power is disconnected.

Md. Code Regs. 11.22.04.05