[Code of Federal Regulations]
[Title 49, Volume 5]
[Revised as of October 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR570.56]

[Page 179-180]
 
                        TITLE 49--TRANSPORTATION
 
                            OF TRANSPORTATION
 
PART 570--VEHICLE IN USE INSPECTION STANDARDS--Table of Contents
 
        Subpart B--Vehicles With GVWR of More Than 10,000 Pounds
 
Sec. 570.56  Vacuum brake assist unit and vacuum brake system.

    The following requirements apply to vehicles with vacuum brake 
assist units and vacuum brake systems.
    (a) Vacuum brake assist unit integrity. The vacuum brake assist unit 
shall demonstrate integrity as indicated by a decrease in pedal height 
when the engine is started and a constant 50-pound force is maintained 
on the pedal.
    (1) Inspection procedure. Stop the engine and apply service brake 
several times to destroy vacuum in system. Depress the brake pedal with 
50 pounds of force and while maintaining that force, start the engine. 
If the brake pedal does not move slightly under force when the engine 
starts, there is a malfunction in the power assist unit.

[[Page 180]]

    (b) Low-vacuum indicator. If the vehicle has a low-vacuum indicator, 
the indicator activation level shall not be less than 8 inches of 
mercury.
    (1) Inspection procedure. Run the engine to evacuate the system 
fully. Shut off the engine and slowly reduce the vacuum in the system by 
moderate brake applications until the vehicle vacuum gauge reads 8 
inches of mercury. Observe the functioning of the low-vacuum indicator.
    (c) Vacuum brake system integrity. (1) The vacuum brake system shall 
demonstrate integrity by meeting the following requirements:
    (i) The vacuum brake system shall provide vacuum reserve to permit 
one service brake application with a brake pedal force of 50 pounds 
after the engine is turned off without actuating the low vacuum 
indicator.
    (ii) Trailer vacuum brakes shall operate in conjunction with the 
truck or truck tractor brake pedal.
    (2) Inspection procedure. (i) Check the trailer vacuum system by 
coupling trailer(s) to truck or truck tractor and opening trailer 
shutoff valves. Start the engine and after allowing approximately 1 
minute to build up the vacuum, apply and release the brake pedal. In the 
case of trailer brakes equipped with brake chamber rods, observe the 
chamber rod movement. Run the engine to re-establish maximum vacuum, 
then shut off the engine and apply the brakes with a 50-pound force on 
the brake pedal. Note the brake application and check for low-vacuum 
indicator activation.
    (ii) For a combination vehicle equipped with breakaway protection 
and no reservoir on the towing vehicle supply line, close the supply 
line shutoff valve and disconnect the supply line. Apply a 50-pound 
force to the brake pedal on the towing vehicle and release. Trailer 
brakes should remain in the applied position.
    (d) Vacuum system hoses, tubes and connections. Vacuum hoses, tubes 
and connections shall be in place and properly supported. Vacuum hoses 
shall not be collapsed, cracked or abraded.
    (1) Inspection procedure. With the engine running, examine hoses and 
tubes for the conditions indicated and note broken or missing clamps.