11.14.04.03

.03 Brakes.

A. Brake Inspection—Heavy Vehicles. Certain items of special interest shall be considered by the inspector when evaluating the braking on large, heavily loaded vehicles.

B. Safety. The vehicle or combination of vehicles may weigh many tons and too much stress cannot be put upon the safety of the inspector and others when testing the stopping ability of the vehicles. These tests shall be conducted with extreme care in order to prevent possible skidding, jackknifing, load shifting, and overturning. In particular, extreme care shall be used in testing liquid cargo-carrying vehicles under partially loaded conditions because of the sudden surging of the cargo.

C. Practicality.

(1) A thorough brake inspection includes the inspection of the inside of the brake assembly. The removal of wheel hubs and drums from large commercial vehicles is difficult because of size and weight problems and extreme care shall be taken to assure they are properly returned to the axle.

(2) A thorough examination of the hydraulic, vacuum, or air systems will normally give a fair idea of general condition of the braking system, especially when augmented by a practical performance demonstration.

D. Service Brake Performance Tests.

(1) Road. Simple tests and visual procedures. Service brake tests shall be conducted on a substantially level, dry, hard, smooth surface road or area that is free from loose material, oil, or grease. Using the service brake only, the stopping ability of the vehicle shall be tested by one of the following methods:

Procedures: Reject Vehicle If:
(a) Service Brake Test: Method (1)—On Road: At a speed of 20 mph apply service brakes firmly. Observe whether the vehicle comes to a smooth stop. (a) Required stopping distance is greater than that contained in brake performance chart.
(b) Service Brake Test: Method (2)— On Road: Mount an approved decelerometer at centerline of vehicle. Level the decelerometer. At the speed of 20 mph, apply service brake firmly. Observe decelerometer reading. Determine whether vehicle pulls to the right or left. (b) The vehicle develops less deceleration than that contained in the brake performance chart.
(c) Vehicle pulls severely to the right or left upon brake application.

(2) Platform Test. Before attempting inspection by this method, the inspector should be trained and experienced in the use of the equipment and the equipment must have adequate capacity.

Procedures: Reject Vehicle If:
(a) Method (3)—Platform Tester:
Drive vehicle onto drive-on-and-stop platform tester. Apply brakes firmly at a speed from 4 to 8 mph without wheel lockup. All braking action shall take place on the platform.
(a) Required stopping distance is greater than that contained in brake performance chart.
(b) This equipment may be used to inspect the relative effectiveness of each wheel. There shall be braking action on all wheels and the action on any one wheel shall be 75 percent or more of the action of the other wheel on the same axle. (b) Any wheel fails to indicate braking action. If the reading on any one wheel is less than 75 percent of the reading on the other wheel on the same axle.

(3) Dynamic Brake Inspection. This test is for stations equipped with a roller-type brake dynamometer. The rollers should be dry, smooth and free of oil or grease. The equipment indicates both braking effort and imbalance. Brakes on front and rear axles are evaluated separately.

Procedures: Reject Vehicle If:
(a) Method (4)—Roller-Type Brake Dynamometer (Force Measuring Type):
  (i) Adjust tire to proper inflation.
 (ii) Position vehicle on dynamometer rolls and begin test.
 (iii) Follow equipment manufacturer's recommended testing procedures.
(a) Readings are less than requirements on brake performance chart.
(b) Any wheel fails to indicate braking action. If the reading on any one wheel is less than 75 percent of the reading on other wheel on the same axle.

E. Hydraulic System.

(1) Tests and visual inspection procedures. Recommended for inspection programs which must accommodate a large volume of vehicles. Results will indicate whether a vehicle has reasonably safe brakes at the time of inspection. The engine shall be running when vehicles are checked with power assisted hydraulic systems. These procedures are applicable to vehicles equipped with hand controls for the physically handicapped.

Procedures: Reject Vehicle If:
(a) Hydraulic System Leakage Test:
While the vehicle is stopped, depress brake pedal under moderate foot force. The pedal height shall remain constant for 1 minute.
(a) Brake pedal height cannot be maintained for 1 minute.
(b)
 (i) Less than 1/3 of the total available pedal travel remains.
(b) Pedal Reserve Test:
 (i) While the vehicle is stopped, depress brake pedal under moderate foot force.
 (ii) On vacuum assisted hydraulic systems with master cylinder booster, pedal travel has no significance. Do not inspect this item.
(c) Air power assist push rod moves slowly toward master cylinder while air pressure is maintained for 1 minute.
(c) Hydraulic system with air power assist test for leakage. Apply 2-3 psi air pressure and maintain for 1 minute.  

(2) At least one wheel and drum assembly shall be removed from each axle equipped with brakes. On disc brakes only wheel assembly removal is necessary. Any wheel or drum assembly removal shall be on alternate sides. Always inspect a brake assembly which shows evidence of leaking fluid or grease. Do not remove hydraulic wheel cylinder dust boots for inspection. Leakage can be determined by pushing on the outside of the boot.

Procedures: Reject Vehicle If:
(a) Hydraulic System—Visually inspect condition of hydraulic system.
  (i) Inspect wheel cylinders for leakage and operation. Do not remove dust covers.
(a)
  (i) Wheel cylinders leak.
  (ii) Inspect hydraulic hoses and brake lines for leaks, cracks, chafing, flattened or restricted section, and improper support.   (ii) Hoses, brake lines are cracked, chafed, flattened, restricted, are rusted and pitting is visible, are insecurely fastened, or lines have been repaired or replaced with copper tubing or other material not designed for hydraulic brake lines. Hoses or brake lines are mounted to contact wheels or body during steering or suspension movement.
  (iii) Inspect master cylinder for leakage and fluid level (be sure no dirt gets into reservoir when cover is removed and that the gasket is serviceable).   (iii) Master cylinder leaks.
  (iv) The fluid level in any section is less than 1/2 full.
  (v) The gasket does not properly seal master cylinder.
  (vi) Wheel cylinders fail to operate.
(b) Dual Hydraulic Circuits—In addition to the above, if vehicle is equipped with a brake warning light:
  (i) Test for operation of light;
  (ii) With ignition switch on, apply moderate foot force, and observe light;
  (iii) Inspect both sections of reservoir.
(b)
  (i) Light is burned out.
  (ii) Light comes on when brake pedal is depressed.
  (iii) The fluid level in any section is less than 1/2 full.
  (c)(i) Brakes fail to function when applied.
   (ii) Brakes do not remain applied until released.

F. Drums and Discs.

(1) Some vehicles have a combination of disc (caliper) type brakes on the front wheels and drum-type brakes on the rear wheels.

(2) On vehicles equipped with disc brakes, some drag can be felt when turning the wheel and tire. This drag is not excessive if the wheel can be turned readily with both hands.

Procedures: Reject Vehicle If:
(a) Brake Drums:
 (i) Inspect the condition of the drum friction surface for any crack extending to the open edge of the drum (short hairline cracks should not be considered).
 (ii) Inspect any crack on the outside of the drum.
 (iii) Inspect for mechanical damage.
 (iv) Inspect for contaminated friction surface.
 (v) Measure inside diameter of drum.
(a)
 (i) There is a crack on the friction surface extending to the open edge of the drum.
 (ii) There is any external crack.
 (iii) There is evidence of excessive mechanical damage other than wear.
 (iv) Friction surface is contaminated with oil, grease, or brake fluid.
 (v) Inside drum diameter is greater than manufacturer's recommended limit, or the diameter stamped on the drum.
(b) Brake Discs (if equipped):
 (i) Inspect for any crack extending to edge of disc.
 (ii) Inspect for mechanical damage.
 (iii) Inspect for contaminated friction surface.
(b)
 (i) There is any crack extending to the edge of the disc.
 (ii) If a crack extends into the weld or more than one-half the outside diameter of a BF Goodrich steel disc.
 (iii) There is evidence of excessive mechanical damage other than wear.
 (iv) Friction surface is contaminated with oil, grease, or brake fluid.
 (v) Thickness of disc is less than manufacturer's recommended limit or the thickness stamped on the disc.

G. Brake Linings and Pads.

Procedures: Reject Vehicle If:
(1) Condition of Linings and Pads:
  (a) Bonded Linings: Measure the lining thickness at the thinnest point.
(1)
  (a) Thinnest point of remaining bonded lining is less than 2/32 inch.
  (b) Riveted Linings:
    (i) Inspect for loose or missing rivets.
    (ii) Measure lining thickness above rivet head at thinnest point.
  (b) Riveted Linings:
    (i) Any rivet is loose or missing.
    (ii) Remaining lining is less than 2/32 inch above any rivet head.
  (c) Wire-Backed Linings: Inspect for wire showing in the friction surface.   (c) Wire backing is visible in the friction surface.
  (d) Bolted Linings (for buses and heavy vehicles):
    (i) Inspect for loose or missing bolts.
    (ii) Measure lining thickness at center of shoe.
  (d) Bolted Linings (for buses and heavy vehicles):
    (i) Any fastening parts are loose or missing.
    (ii) Remaining lining is less than 5/16 inch at center of shoe.
  (e) All linings: Inspect for broken or cracked linings, and parts of linings not firmly attached to shoe. Also inspect for contamination and excessively uneven lining wear.   (e)(i) Lining is broken, cracked, or not firmly and completely attached to shoe.
    (ii) Friction surface is contaminated with oil or grease.
    (iii) Lining wear is extremely uneven.
  (f) Pads (Disc Brakes): Inspect thickness of friction pads. Many newer disc brake friction pads for vehicles in excess of 10,000 pounds GVWR are manufactured with a heat dissipator which is, in most instances, approximately 7/32 of an inch thick between the friction pad and the metal pad plate. These dissipators, if allowed to contact the rotor, will cause damage to the rotor. Therefore, when measuring disc brake friction pad thickness, it must first be determined if the braking system being inspected is equipped with these heat dissipators. If heat dissipators are present, the brake friction pad thickness shall be measured so that no portion of the heat dissipator is included in the measurement. If no heat dissipators are present, the brake friction pad thickness will be measured in the normal manner to the metal pad plate or rivets.    (f)(i) Any pad is less than 2/32 inch.
    (ii) Any pad on BF Goodrich Air Actuated Disc Brakes has 1/8 inch or less lining remaining.

H. Mechanical Linkage. Includes the parking brake and manual brake controls on vehicles equipped for physically handicapped persons.

Procedures: Reject Vehicle If:
(1) Condition of Mechanical Components: (1)
 (a) Inspect for worn pins and missing or defective cotter pins.  (a) Mechanical parts are missing, broken, or badly worn.
 (b) Inspect for broken, missing or worn springs, cables, clevises, couplings, rods, and anchor pins.  (b) Grease retainers are leaking (dampness is not cause for rejection).
 (c) Inspect for frozen, rusted, or inoperative connections, missing spring clips, and defective grease retainers.  (c) There is excessive friction in pedal and linkage or in brake components.
 (d) Inspect pedal shaft and bearings for high friction, wear, and misalignment.  (d) Pedal levers are improperly positioned or misaligned.
 (e) Inspect for restriction of shoe movement at backing plate and for binding between brake shoes and anchor pins.  (e) Conversion of a self-adjusting mechanism that is not completely converted.

I. Vacuum System.

Procedures: Reject Vehicle If:
(1) Condition of Vacuum Booster System: Visually inspect system for collapsed, broken, badly chafed, and improperly supported hoses and tubing, and loose or broken hose. clamps. (1)
 (a) Hoses and tubing are leaking, collapsed, broken, badly chafed, improperly supported, or loose because of broken clamps.
 (b) Hose or tubing is in good condition but exposed to danger from excessive heat, flying debris or rubbing.
(2) Operation of Vacuum Booster System:
 (a) Determine whether system is operating by first stopping engine, then depress brake pedal several times to deplete all vacuum in system.
 (b) Then depress pedal with a light force. While maintaining this force on the pedal, start engine, and observe whether pedal moves slightly when engine starts.
(2) Service brake pedal does not move slightly when engine is started while pressure is maintained on pedal.
(3) Vacuum Reserve and Low Vacuum Indicators:
 (a) Build full vacuum, then shut off engine and make as many full brake applications as possible.
 (b) On vehicles with low vacuum indicator, build full vacuum, then shut off engine and reduce vacuum by making a series of moderate brake applications. A visible or audible signal should function when vacuum reaches 8 inches Hg on gauge.
(3)
 (a) Vacuum reserve is insufficient to make one full application after engine shutoff.
 (b) Indicator fails to function when the system is reduced to 8 inches Hg vacuum.

J. Air System—Function: Compressor—Low Indicator—Governor.

Procedures: Reject Vehicle If:
(1) With air system fully charged, open all drain cocks in the system until gauge indicates zero pressure. (1) Time required to build pressure from 50—90 psi at fast idle exceeds:
 (a) Single unit vehicle and school vehicle—3 minutes; or
 (b) Combination vehicle—5 minutes.
(2) Then close drain cocks and run engine at fast idle; record time to raise air pressure from 50—90 psi on gauge. (2) Low pressure warning fails to function when pressure is lowered to 60 psi.
(3) Observe gauge pressure at which signal on low pressure indicator goes out or off. (3) Governor cut-out pressure is higher than 135 psi.
(4) Continue running engine and observe gauge pressure when governor cuts out. (4) Governor cut-in pressure is lower than 80 psi.
(5) With engine idling, make a series of brake applications and observe pressure when governor cuts in.

K. Air Leakage and Reserve. It may be desirable to install in the system an air gauge (0—150 psi) which has 5 or 10 psi increments, so that small changes in pressure can be more easily observed.

Procedures: Reject Vehicle If:
(1) Air Leakage in System:
Inspection for air leakage shall be made in two ways:
(1) Leakage exceeds the following limits:
  Brakes Fully Applied Brakes Released
 (a) With a fully charged system, stop engine and record the pressure drop in psi per minute with brakes fully applied.
 (b) With a fully charged system, stop engine and record the pressure drop in psi per minute with brakes released.
Single unit school vehicles—3 psi per minute. Combination vehicles—4 psi per minute. Single unit vehicles and school vehicles—2 psi per minute. Combination vehicles—3 psi per minute.
(2) Compressed Air Reserve:
 (a) Make a series of brake applications until low pressure warning signal operates. Stop engine and make one full brake application.
 (b) With a fully charged system, stop engine and make one full brake application. Measure drop in reservoir pressure.
(2)
 (a) Air reserve is not sufficient to permit one full brake application after engine is stopped.
 (b) Reservoir pressure is lowered more than 20 percent of the first reading.
(3) General Condition:
 (a) Inspect all air hoses, tubes, and connections. Check attachments of all connecting lines and look for proper supporting parts. Be sure lines are free from contact with frame, axles, exhaust system, or other lines.
 (b) Inspect for leaks that may be heard from valves, diaphragms, piston cups, and connections.
 (c) Inspect air pressure relief valve, tension and condition of compressor drive belts. Check air intake cleaner for being clogged or restricted.
(3)
 (a) There are leaks, breaks, crimps, or cracks in the air hoses, tubes, or connections.
 (b) Lines are being chafed by moving parts, or are touching the exhaust system.
 (c) Leaks in valves, diaphragms, piston cups, or connections can be heard.
 (d) Air pressure relief valve does not operate.
 (e) Compressor drive belts are badly worn, frayed, or loose.
 (f) Air intake cleaner is clogged or restricted enough to prevent proper air intake.

L. Air Brakes—Parking and Emergency Systems. Commercial buses and some trucks may be equipped with hand-operated controls for parking and emergency air brake systems.

Procedures: Reject Vehicle If:
(1) Air Brake Parking and Emergency Systems:
 (a) With air pressure in the braking system at operational level, set parking brake control and observe functioning of parking and emergency braking at wheels.
(1)
 (a) System fails to function properly.
 (b) Vehicle can be moved with zero air pressure in system.
 (b) Drain air from the system and observe whether parking and emergency brakes remain in an applied position (with no air pressure in the system, vehicle should remain "braked").  

M. Actuator Reserve.

Procedures: Reject Vehicle If:
(1) Actuator Reserve Test:
 (a) On air or vacuum mechanical brakes, measure the stroke of the air or vacuum chambers from fully released to fully applied position.
 (b) On air-over-hydraulic brake systems, measure air chamber travel from fully released to fully applied position (some systems include a rod gauge for visual checking).
(1)
 (a) The push rod travel on S-Cam Brakes exceeds the maximum stroke listed in S-Cam Brakes—Push Rod Travel Limits Chart.
   (i) Push rod travel on BF Goodrich Air Actuated Disc Brakes exceeds manufacturer's specification.
(2) Push Rod/Slack Adjuster Angle: Measure push rod/slack adjuster angle with brakes applied. (2) Push rod/slack adjuster angle is less than 90 degrees with brakes applied.
(3) Wedge Brakes Shoe Movement: Measure total shoe movement from released to applied positions. (3) Brake shoe movement on wedge brakes exceeds 1/16 inch.

Figure 16—BRAKE CHAMBER PUSH ROD TRAVEL(TYPICAL).

N. Emergency Brakes. To avoid confusion between emergency and parking brake systems, refer to definitions (see §T). On vehicles equipped with spring-type emergency brake systems, manual operation of the control valve will also provide an effective parking brake system.

Procedures: Reject Vehicle If:
(1) Emergency System—Function:
 (a) Fully apply the emergency operating control, or release air pressure from the spring brake actuator using the manual control valve. Then:
   (i) Observe locking and holding feature of the actuating mechanism.
   (ii) Observe operating mechanism for "bottoming" before brakes are fully applied.
   (iii) Observe if spring brakes apply when control valve is manually operated.
   (iv) Inspect for worn, missing, or defective cotter pins, springs, rods, yokes, couplings, or anchor pins and cables.
   (v) Observe if mechanism releases brakes when release control is operated.
(1)
 (a)
   (i) Operating mechanism fails to hold brakes in applied position without manual effort.
   (ii) Operating mechanism "bottoms" before brakes are fully applied.
   (iii) Spring brakes fail to apply when control valve is operated.
   (iv) Mechanical parts are missing, broken, or badly worn, or pull cables are badly worn, stretched, frayed, or not operating freely.
   (v) Brakes do not fully release when release control is operated.
(2) Emergency System—Performance:
 (a) Method. At a speed of 10 mph apply emergency brake firmly. Vehicle must come to a stop within a reasonable distance.
 (b) Method. Mount and level an approved decelerometer at centerline of vehicle. At a speed of 20 mph, apply emergency brake firmly. Observe decelerometer reading.
(2)
 (a) The vehicle fails to stop within a reasonable distance after emergency brake application.
 (b) A decelerometer reading of at least 6 feet per second per second cannot be obtained.

O. Parking Brakes. An emergency brake can also serve as a parking brake but a parking brake is not adequate to serve as an emergency brake. Most large vehicles with hydraulic brake systems and some large vehicles with air brake systems will have a parking brake located on the propeller (drive) shaft. This type of parking brake is usually open and easily inspected.

Procedures: Reject Vehicle If:
(1) Set the parking brake firmly to determine the reserve travel of the hand lever or foot pedal. (1)
 (a) There is less than 1/3 pedal or lever reserve remaining.
 (b) Brake fails to hold the vehicle on any grade on which it is operated.
(2) Inspect the band or disc-type parking brake on the propeller (drive) shaft for the presence of oil or grease, condition of lining and adjustment. (2)
 (a) There is oil or grease on the drum, disc, or lining.
 (b) The lining is worn through to the steel band or shoe.
 (c) The lining fails to make proper contact with the drum or disc when brake is applied.
(3) Spring-type parking air brake system—inspect only for setting and release, not for travel reserve of the hand lever or foot pedal. (3) Spring-type parking air brake system fails to set or release.

P. Brake Performance Chart. As of July 1, 1972, all vehicles subject to the regulations of the Bureau of Motor Carrier Safety are subject to the stopping requirements in this Brake Performance Chart except the column pertaining to Emergency Brake System, which are effective on vehicles manufactured after July 1, 1973.

  Service Brake Systems Emergency
Brake Systems
I II III IV V
  Braking force
as a percentage
of gross vehicle
or combination
weight
Deceleration
in feet per
second per
second
Application
and braking
distance in
feet from
initial speed
of 20 mph
Application
and braking
distance in
feet from
initial speed
of 20 mph
(1) Passenger-carrying vehicles.
(a) Vehicles with a seating capacity of 10 persons or less, including driver, and built on a passenger car chassis.
65.2 21 20 54
(b) Vehicles with a seating capacity of more than 10 persons, including driver, and built on a passenger car chassis; vehicles built on a truck or bus chassis and having a manufacturer's GVWR of 10,000 pounds or less. 52.8 17 25 66
(c) All other passenger-carrying vehicles (including motorcycles). 43.5 14 35 85
(2) Property-carrying vehicles.
 (a) Single unit vehicles having a manufacturer's GVWR of 10,000 pounds or less.
52.8 17 25 66
(b) Single unit vehicles having a manufacturer's GVWR of more than 10,000 pounds except truck tractors. Combinations of a 2-axle towing vehicle and trailer having a GVWR of 3,000 pounds or less. All combinations of 2 or less vehicles in drive-away or tow-away operation. 43.4 14 35 85
(c) All other property-carrying vehicles and combinations of property-carrying vehicles. 43.5 14 40 90
Explanation of §P

(1) This deceleration as measured in brake tests cannot be used to compute the values in Column 4 because it is not sustained at the same rate over the entire period of the stop. The deceleration increases from zero to a maximum during a period of brake system application and brake force build-up. Also, other factors may cause the deceleration to decrease after reaching a maximum. The added distance which results because of a maximum deceleration is not sustained is included in the figures in Column 4 but is not indicated by usual brake testing devices for checking deceleration.

(2) There is a definite mathematical relationship between the figures in Columns 2 and 3. If the decelerations set forth in Column 3 are divided by 32.2 feet per second per second, the Column 2 figures will be obtained (for example, 17 divided by 32.2 gives 52.8 percent). Column 2 is included in the tabulation because certain brake testing devices utilize this factor.

(3) The decelerations as in Column 3 are an indication of the effectiveness of the basic brakes, and as measured in practical brake testing are the maximum braking decelerations attained at sometime during the stop.

(4) The distances in Column 4 and the decelerations in Column 3 are not directly related. Brake system "application and braking distance in feet" (Column 4) is a definite measure of the overall effectiveness of the braking system, being the distance traveled between the point at which the driver starts to move the braking controls and the point at which the vehicle comes to rest. It includes distance traveled while the brakes are being applied and the distance traveled while the brakes are retarding the vehicle.

(5) The distance traveled during the period of brake system application and brake force buildup varies with vehicle type, being negligible for many passenger cars and greatest for combinations of commercial vehicles. This fact accounts for the variation from 20 to 40 feet in the numerical values in Column 4 for the various classes of vehicles.

(6) The deceleration requirement in Column 3 is the same for all classifications of vehicles except for passenger vehicles, not including buses, because brakes on vehicles in the second, third and fourth classifications are all capable with reasonable maintenance of producing the designated deceleration as measured by brake testing devices. A higher deceleration requirement is warranted for passenger cars in view of United States Department of Transportation/Federal Highway Administration test data.

Q. Decelerometers.

(1) The method of brake system application and braking distance is not to be confused with the distance indicated by the inertia-type decelerometer and other existing brake testers, which often are purported wrongly to measure the vehicle stopping distance.

(2) The pendulum and U-tube decelerometers used for brake testing are instruments scaled to read deceleration or equivalent braking force (sometimes referred to as brake efficiency) in percentages. The principle of the pendulum-type decelerometer is that a pendulum on a vehicle moving at a uniform speed will assume a vertical position. When the vehicle speed is reduced by application of the brakes, the pendulum will swing forward to an angle away from the vertical. The tangent of the angle through which the pendulum moves is directly proportional to the deceleration. Basically, the U-tube fluid-type instrument is a closed glass tube formed in the shape of a U. When vehicle speed is reduced by braking, the inertia of the fluid causes the level in the glass tube to fall. The distance the level of the liquid falls is proportional to the deceleration in feet per second per second, which is read from a scale on the front part of the glass tube.

(3) The vehicle will normally pitch because the lines of action of the inertia and braking forces are different. In order to minimize erroneous responses, the decelerometer, if used, should be put as close to the center of the vehicle as practical.

R. Brake Testing Machines.

(1) These types of brake testers measure braking force at each wheel. The effectiveness of the brake testers that measure braking force in the testing of vehicles other than passenger vehicles or light trucks is very questionable.

(2) The dimensions of these brake testers do not permit practical and reliable testing on combination vehicles. Use should therefore be restricted to two-axle vehicles. The simulated road surface of surface of these machines will occasionally exhibit much higher coefficients of friction than is possible on the highway. Excessive braking should therefore be avoided, be avoided, because braking distribution information is distorted.

(3) For drive-on-and-stop test machines, the vehicle is driven on the pads at speeds of 4 to 8 mph. When the brakes are applied at the time the vehicle is moving on the pads, the braking effort at each wheel causes a proportionate movement of the pad against the measuring system. The braking force on the pads is measured by indicating or recording instruments.

(4) The roller-type brake testing machine has powered rollers that turn the individual wheels while the brakes are applied in order to measure the brake force developed.

S. Test Wheel Equipment. Any type of fifth or test wheel equipment can be used, if it obtains the following results:

(1) It measures the distance within plus or minus 3 percent of the values obtained by the "hot-shot" method, which uses an electrically fired gun.

(2) The road speed of the test wheel is measured with a speedometer designed to hold the indicating hand at the speed from which the stop is initiated. The speedometer shall indicate the speed to within plus or minus 2 percent of the speed timed with a stopwatch over a measured mile.

T. Definitions.

(1) "Brake system" means a combination of one or more brakes and their related means of operation and control.

(2) "Deceleration" means the rate of reduction of the speed of the vehicle, expressed in feet per second per second.

(3) "Equivalent braking ratio" means the percentage ratio of the sum of retarding forces developed by each braked wheel to the "as tested" gross weight of the vehicle or combination.

(4) "Emergency brake system" means a brake system used for retarding and stopping the vehicle in the event of a malfunction in the service brake system (this function may be performed by the parking brake system or by a portion of the service brake system, or by a separate brake system).

(5) "Parking brake system" means a brake system used to hold and maintain a vehicle in a stationary position (a positive mechanical means is employed to hold the brake applied when the vehicle is unattended).

(6) "Pedal reserve" as applied to hydraulic, mechanical, or power-assisted hydraulic brakes, means the amount of total pedal travel left in reserve when the pedal is depressed to the brake-applied position (the purpose of the pedal reserve check is to ascertain the degree of the brake adjustment and to demonstrate satisfactory brake actuating system condition).

(7) "Service brake system" means a brake system used for retarding, stopping, and controlling the vehicle under normal operating conditions.

(8) "Stopping distance" means the distance traveled by a vehicle from the point of application of force to the brake control, to the point at which the vehicle reaches a full stop.