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

[(A ¥ B) / A] × 100 (c) system integrity. (1) The vacuum brake system shall dem- The engine must be operating when onstrate integrity by meeting the fol- power-assisted are checked. lowing requirements: (d) Brake hoses, 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 vehicle 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 truck or sion. Master cylinder shall not show truck tractor brake pedal. signs of leakage. Hose 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- vehicles 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.

231

VerDate Mar<15>2010 14:39 Dec 20, 2010 Jkt 220217 PO 00000 Frm 00241 Fmt 8010 Sfmt 8010 Y:\SGML\220217.XXX 220217 jdjones on DSKHWCL6B1PROD with CFR