Nat’l Highway Traffic Safety Admin., DOT § 570.57

[(A ¥ B) / A] × 100 (c) Vacuum system integrity. (1) The system shall dem- The engine must be operating when onstrate integrity by meeting the fol- power-assisted are checked. lowing requirements: (d) Brake , master cylinder, tubes (i) The vacuum brake system shall and tube assemblies. provide vacuum reserve to permit one hoses shall not be mounted so as to service brake application with a brake contact the body or chassis. pedal force of 50 pounds after the en- Hoses shall not be cracked, chafed, or gine is turned off without actuating flattened. Brake tubes shall not be flat- the low vacuum indicator. tened or restricted. Brake hoses and tubes shall be attached or supported to (ii) Trailer vacuum brakes shall oper- prevent damage by vibration or abra- ate in conjunction with the or sion. Master cylinder shall not show truck tractor brake pedal. signs of leakage. or tube protec- (2) Inspection procedure. (i) Check the tive rings or devices shall not be con- trailer vacuum system by coupling sidered part of the hose or tubing. trailer(s) to truck or truck tractor and (1) Inspection procedure. Examine vis- opening trailer shutoff valves. Start ually brake master cylinder, hoses and the engine and after allowing approxi- tubes, including front brake hoses, mately 1 minute to build up the vacu- through all wheel positions from full um, apply and release the brake pedal. left turn to full right turn for condi- In the case of trailer brakes equipped tions indicated. with brake chamber rods, observe the chamber rod movement. Run the en- [39 FR 26027, July 16, 1974, as amended at 40 FR 5160, Feb. 4, 1975] gine to re-establish maximum vacuum, then shut off the engine and apply the § 570.56 Vacuum brake assist unit and brakes with a 50-pound force on the vacuum brake system. brake pedal. Note the brake applica- The following requirements apply to tion and check for low-vacuum indi- with vacuum brake assist cator activation. units and vacuum brake systems. (ii) For a combination vehicle (a) Vacuum brake assist unit integrity. equipped with breakaway protection The vacuum brake assist unit shall and no reservoir on the towing vehicle demonstrate integrity as indicated by supply line, close the supply line shut- a decrease in pedal height when the en- off valve and disconnect the supply gine is started and a constant 50-pound line. Apply a 50-pound force to the force is maintained on the pedal. brake pedal on the towing vehicle and (1) Inspection procedure. Stop the en- release. Trailer brakes should remain gine and apply service brake several in the applied position. times to destroy vacuum in system. (d) Vacuum system hoses, tubes and Depress the brake pedal with 50 pounds connections. Vacuum hoses, tubes and of force and while maintaining that connections shall be in place and prop- force, start the engine. If the brake erly supported. Vacuum hoses shall not pedal does not move slightly under be collapsed, cracked or abraded. force when the engine starts, there is a (1) Inspection procedure. With the en- malfunction in the power assist unit. gine running, examine hoses and tubes (b) Low-vacuum indicator. If the vehi- for the conditions indicated and note cle has a low-vacuum indicator, the in- broken or missing clamps. dicator activation level shall not be less than 8 inches of mercury. § 570.57 system and air-over- (1) Inspection procedure. Run the en- hydraulic brake subsystem. gine to evacuate the system fully. Shut The following requirements apply to off the engine and slowly reduce the vacuum in the system by moderate vehicles with air brake and air-over- brake applications until the vehicle hydraulic brake systems. Trailer(s) vacuum gauge reads 8 inches of mer- must be coupled to a truck or truck- cury. Observe the functioning of the tractor for the purpose of this inspec- low-vacuum indicator. tion, except as noted.

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(a) Air brake system integrity. The air applied. There may be an additional 1 brake system shall demonstrate integ- psi drop per minute for each additional rity by meeting the following require- towed vehicle. ments: (7) The drive belt shall (1) With the vehicle in a stationary not be badly worn or frayed and belt- position, reserve shall tension shall be sufficient to prevent be sufficient to permit one full service slippage. brake application, after the engine is Inspection procedure. With the air sys- stopped and with the system fully tem charged, open the drain cocks in charged, without lowering reservoir the service and supply reservoir on the pressure more than 20 percent below truck or truck-tractor. Note the pres- the initial reading. sure at which the visual or audible (2) The air brake system compressor warning device connected to the low- shall increase the air pressure in the pressure indicator is activated. Close reservoir(s) from the level developed the drain cocks, and, with the trailer(s) after the test prescribed in § 570.57(a)(1) uncoupled, check air pressure buildup to the initial pressure noted before the at the manufacturer’s recommended full brake application, with the engine engine speed. Observe the time re- running at the manufacturer’s max- quired to raise the air pressure from 85 imum recommended number of revolu- to 100 psi. Continue running the engine tions per minute with the compressor until the governor cuts out and note governor in the cut-off position, in not the pressure. Reduce engine speed to more than 30 seconds for vehicles man- idle, couple the trailer(s), if applicable, ufactured prior to March 1, 1975. For and make a series of brake applica- vehicles, manufactured on or after tions. Note the pressure at which the March 1, 1975, the time allowed for air governor cuts in. Increased engine pressure buildup shall not exceed 45 speed to fast idle and charge the sys- seconds. tem to its governed pressure. Stop the (3) The warning device (visual or au- engine and record the pressure drop in dible) connected to the brake system psi per minute with brakes released air pressure source shall be activated and with brakes fully applied. when air pressure is lowered to an acti- (b) Air brake system hoses, tubes and vating level that is not less than 50 psi. connections. Air system tubes, hoses For vehicles manufactured to conform and connections shall not be restricted, to Federal Motor Vehicle Safety cracked or improperly supported, and Standard No. 121, the low-pressure indi- the air hose shall not be abraded. cator shall be activated when air pres- (1) Inspection procedure. Stop the en- sure is lowered to an activating level gine and examine air hoses, tubes and that is not less than 60 psi. connections visually for conditions (4) The governor cut-in pressure shall specified. be not lower than 80 psi, and the cut- (c) Air-over-hydraulic brake subsystem out pressure shall be not higher than integrity. The air-over-hydraulic brake 135 psi, unless other values are rec- subsystem shall demonstrate integrity ommended by the vehicle manufac- by meeting the following requirements: turer. (1) The air brake system compressor (5) Air brake pressure shall not drop shall increase the air pressure in the more than 2 psi in 1 minute for single reservoir(s) from the level developed vehicles or more than 3 psi in 1 minute after the test prescribed in § 570.57(a)(1) for combination vehicles, with the en- to the initial pressure noted before the gine stopped and service brakes re- full brake application, with the engine leased. There may be an additional 1 running at the manufacturer’s rec- psi drop per minute for each additional ommended number of revolutions per towed vehicle. minute and the compressor governor in (6) With the reservoir(s) fully the cut-out position, in not more than charged, air pressure shall not drop 30 seconds for vehicles manufactured more than 3 psi in 1 minute for single prior to March 1, 1975. For vehicles vehicles or more than 4 psi in 1 minute manufactured on or after March 1, 1975, for combination vehicles, with the en- the time for air pressure build up shall gine stopped and service brakes fully not exceed 45 seconds.

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(2) The warning device (visual or au- erly supported, the air and hydraulic dible) connected to the brake system hoses shall not be abraded and the mas- air pressure source shall be activated ter cylinder shall not show signs of when the air pressure is lowered to not leakage. less than 50 psi. (1) Inspection procedure. Stop the en- (3) The governor cut-in pressure shall gine and examine air and hydraulic be not lower than 80 psi, and the cut- brake hoses, brake master cylinder, out pressure shall not be higher than tubes and connections visually for con- 135 psi, unless other values are rec- ditions specified. ommended by the vehicle manufac- turer. [39 FR 26027, July 16, 1974, as amended at 40 (4) Air brake pressure shall not drop FR 5160, Feb. 4, 1975; 41 FR 13924, Apr. 1, 1976] more than 2 psi in 1 minute for single § 570.58 Electric brake system. vehicles or more than 3 psi in 1 minute for combination vehicles, with the en- (a) Electric brake system integrity. The gine stopped and service brakes re- average brake amperage value shall be leased. Allow a 1-psi drop per minute not more than 20 percent above, and for each additional towed vehicle. not less than 30 percent below, the (5) With the reservoir(s) fully brake manufacturer’s maximum cur- charged, air pressure shall not drop rent rating. In progressing from zero to more than 3 psi in 1 minute for single maximum, the ammeter indication vehicles or more than 4 psi in 1 minute shall show no fluctuation evidencing a for combination vehicles, with the en- short circuit or other interruption of gine stopped and service brakes fully current. applied. Allow a 1-psi pressure drop in (1) Inspection procedure. Insert a low 1 minute for each additional towed ve- range (0 to 25 amperes for most 2- and hicle. 4-brake systems and 0 to 40 amperes for (6) The compressor drive belt shall a 6-brake system) d.c. ammeter into not be badly worn or frayed and belt the brake circuit between the con- tension shall be sufficient to prevent troller and the brakes. With the con- slippage. troller in the ‘‘off’’ position, the amme- Inspection procedure. With the air sys- ter should read zero. Gradually apply tem charged, open the drain cocks in the controller to the ‘‘full on’’ position the service and supply reservoir on the for a brief period (not to exceed 1 truck or truck-tractor. Note the pres- minute) and observe the maximum am- sure at which the visual or audible meter reading. Gradually return the warning device connected to the low controller to ‘‘full off’’ and observe re- pressure indicator is activated. Close turn to zero amperes. Divide the max- the drain cocks and, with the trailers imum ammeter reading by the number uncoupled, check air pressure buildup of brakes and determine the brake am- at the manufacturer’s recommended perage value. engine speed. Observe the time re- (b) Electric brake wiring condition. quired to raise the air pressure from 85 Electric brake wiring shall not be to 100 psi. Continue running the engine frayed. Wiring clips or brackets shall until the governor cuts out and note not be broken or missing. Terminal the pressure. Reduce engine speed to connections shall be clean. Conductor idle, couple trailers, and make a series wire gauge shall not be below the brake of brake applications. Note the pres- manufacturer’s minimum rec- sure at which the governor cuts in. In- ommendation. crease engine speed to fast idle and (1) Inspection procedure. Examine vis- charge the system to its governed pres- ually for conditions specified. sure. Stop the engine and record the pressure drop in psi per minute with § 570.59 Service brake system. brakes released and with brakes fully (a) Service brake performance. Compli- applied. ance with any one of the following per- (d) Air-over-hydraulic brake subsystem formance criteria will satisfy the re- hoses, master cylinder, tubes and connec- quirements of this section. Verify that tions. System tubes, hoses and connec- tire inflation pressure is within the tions shall not be cracked or improp- limits recommended by the vehicle

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