11.14.02.03

.03 Brakes.

A. Service Brake Performance Tests.

(1) Road 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:
Service Brake Test.
  (a) Method (1)—On Road. At a speed of 20 mph apply service brakes firmly. Observe whether vehicle comes to a smooth stop within the distance prescribed by law; passenger cars 25 feet, type II school vehicles, light trucks, vans and multipurpose passenger vehicles 30 feet without pulling to the right or left. Driver shall have firm control of the steering wheel throughout the test.
  (a) The vehicle stopping distance requires more than 25 feet for passenger cars, and 30 feet for type II school vehicles, light trucks, vans and multipurpose passenger vehicles.
  (b) Method (2)—On Road. Mount an approved decelerometer at centerline of vehicle. Level at decelerometer.At the speed of 20 mph, apply service brake firmly. Observe decelerometer reading. Determine whether vehicle pulls to right or left.   (b) Vehicle pulls to the right or left upon brake application.
    (c) A decelerometer reading of at least 17 feet psps for passenger cars, 14 psps for type II school vehicles, light trucks, vans and multipurpose passenger vehicles, or pulls to the right or left.

(2) Station test and visual inspection procedures. 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 lock-up. All braking action shall take place on the platforms. Certain models of platform testing equipment are not generally sensitive enough to read the rear axle effort of front wheel drive vehicles.   (a) Readings are less than requirements on brake performance chart in H.
(b) These machines may be used to inspect the relative effectiveness of each wheel.There shall be braking action on all wheels. The action on any one wheel shall be 75 percent or more of the action on the other wheel on the same axle. If there is little or no braking brakes are applied with vehicle jacked action on the rear axle, jack or hoist the vehicle, apply the brakes, and attempt to turn the rear wheels.   (b) Any wheel fails to indicate braking action except as noted, or if the reading on any one wheel is less than 75 percent of the reading on the other wheel on the same axle.
    (c) Rear wheels rotate freely when brakes are applied with vehicle jacked or hoisted.

(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 machine 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).   (a) Readings are less than requirements on brake performance chart in H.
   (i) Adjust tire to proper inflation.
   (ii) Position vehicle on dynamometer rolls and begin test.
   (iii) Follow equipment manufacturer's recommended testing procedures.
   (iv) If there is little or no braking action on the rear axle, jack or hoist the vehicle and apply the brakes and attempt to turn the rear wheels.
  (b) Any wheel fails to indicate braking action except as noted in procedures, or the reading on any one wheel is less than 75 percent of the reading on the other wheel on the same axle.
    (c) Rear wheels rotate freely when brakes are applied with vehicle jacked or hoisted.

B. Hydraulic System.

(1) Tests and visual inspection procedures. Recommended for inspection programs which must accommodate a large volume of vehicles. Results will indicate whether or not a vehicle has reasonably safe brakes at the time of inspection. The engine shall be running when checking vehicles 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) Pedal Reserve Test.While the vehicle is stopped, depress brake pedal under moderate foot force.   (b) Less than 1/3 of the total available pedal travel remains.

(2) At least one front and one opposite rear wheel shall be removed for brake inspection. When any deficiency is noted upon inspection of a wheel pulled, the other wheel on the same axle shall also be pulled for complete brake inspection. Always inspect a brake assembly which shows evidence of leaking fluid or grease. Do not remove 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.
    (ii) Inspect hydraulic hoses and brake lines for leaks, cracks, chafing, flattened or restricted sections, improper support, rusting causing pitting, and improper material.
    (iii) Inspect master cylinder for leakage and fluid level of all sections. (Be sure no dirt gets into reservoir when cover is removed and that the gasket is serviceable.)
  (a)
    (i) Wheel cylinder leaks or fails to operate.
    (ii) Hoses, or brake lines are cracked, chafed, flattened, restricted, or are rusted and pitting is visible, are improperly supported, 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) 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.
  (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, observe light.
  (b)
    (i) Light is burned out.
    (ii) Light comes on when brake and pedal is depressed.

C. Drums and Discs.

(1) Many of today's 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.

(3) Annually all wheels and brake drums shall be removed for brake inspection on type II school vehicles.

Procedures: Reject Vehicle If:
  (a) Brake Drums.
    (i) Inspect the condition of the drum friction surface for substantial cracks extending to the open edge of the drum.(Short hairline heat check cracks should not be considered.)
    (ii) Inspect for cracks on the outside of the drum.
    (iii) Inspect for mechanical damage.
    (iv) Inspect for contaminated friction surface.
    (v) Measure inside diameter of drum.
    (vi) When the drum pulled has any deficiency noted, the other drum on the same axle shall also be pulled and inspected.
  (a)
    (i) There is a substantial crack on the friction surface extending to the open edge.
    (ii) There is an 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 the diameter stamped on the drum, or, if the drum is not stamped, the manufacturer's maximum allowable remachining specification. If the drum is not stamped and no manufacturer's specification exists and the original diameter of the drum can be determined, the inside diameter may be no more than 0.090 inch greater than the original diameter.
  (b) Brake Discs.
   (i) Inspect for substantial cracks extending to edge of disc.
    (ii) Inspect for mechanical damage.
    (iii) Inspect for contaminated friction surface.
    (iv) When the disc brake assembly inspected has any deficiency noted, the other disc brake assembly on the same axle shall also be inspected.
(b)
    (i) There are substantial cracks extending to edge.
    (ii) There is evidence of excessive mechanical damage other than wear.
    (iii) Friction surface is contaminated with oil, grease, or brake fluid.
    (iv) Thickness of disc is less than manufacturer's recommended limit or the minimum thickness stamped on the assembly.

D. Linings and Pads. Remove at least one front and one rear wheel and drum assembly on opposite sides for inspection of linings on drum brakes. On vehicles equipped with disc brakes, only removal of the wheel is necessary. When any deficiency is noted in the linings or pads on the wheel pulled, the linings or pads for the other wheel on the same axle shall also be inspected.

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 lining is less than 2/32 inch.
    (b) Riveted Linings. Inspect for loose or missing rivets. Measure lining thickness above rivet head at thinnest point.     (b) Any rivets are loose or missing.If lining is worn to where less than 1/32 inch remains above any rivethead.
    (c) Wire-Backed Linings. Inspect for wire showing on the friction surface of the lining.     (c) Wire backing is visible on the friction surface.
    (d) 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.     (d) Lining is broken, cracked, or not firmly and completely attached to shoe. Circumferential heat cracks in bonded linings are not cause for rejection if the lining is securely attached to the shoe. If friction surface is contaminated with oil, grease, or brake fluid. If lining wear is extremely uneven.
    (e) Pads (Disc Brakes). Inspect thickness of friction pads. Bonded pads—measure thinnest point of lining. Riveted pads—measure thickness of lining above rivet head.     (e) Lining on any bonded pad is less than 2/32 inch, or less than 2/32 inch lining remains above rivet head.

E. Mechanical Linkage. Includes the service brake mechanism, parking brake, and manual 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.
   (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) Any conversion of self-adjusting mechanism that is not completely converted.
   (f) Inspect service brake pedal rubber pads for excessive wear or missing pads.    (f) Rubber service brake pedal pad is excessively worn to expose metal pedal or rubber pad is missing.

F. Vacuum/Hydraulic Booster System.

Procedures: Reject Vehicle If:
(1) (1)
    (a) 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.    (a) Hoses and tubing are leaking, collapsed, broken, badly chafed, improperly supported, or loose because of broken clamps.
   (b) Operation of Vacuum Booster System.
    (i) Determine if system is operating by first stopping engine than depress brake pedal several times to deplete all vacuum in system.
   (ii) Then depress pedal with a light force. While maintaining this force on the pedal, start engine, and observe if pedal moves slightly when engine starts.
   (b) Service brake pedal does not move slightly when engine is started while pressure is maintained on pedal.
   (c) Condition of hydraulic booster system. Visually inspect system for proper fluid level, broken, kinked, or restricted hoses or lines and any leaks at the pump, steering box, booster, hoses, or lines.    (c) Fluid level in reservoir is less than manufacturer's recommendations; there are broken, kinked, or restricted hoses or lines; or there are leaks at the steering pump.
   (d) Operation of hydraulic booster system.
    (i) Determine if system is operating by first stopping the engine, then depress brake pedal several times to deplete all reserve pressure in the system.
    (ii) Then depress pedal with light force, start engine and observe if pedal moves slightly when engine starts.
   (d) Service brake pedal does not move slightly when engine is started while pressure is maintained.

G. Parking Brake.

(1) Parking Brake Function. Parking brakes on most vehicles function through at least one set of the rear service brake shoes. A few vehicles have disc-type service brakes on all four wheels which makes it necessary to have separate drums for the parking brakes. These drums and linings shall be inspected in a manner similar to that for service drum brakes. Any parking brake shall hold a stopped vehicle firmly on all normal road grades.

Procedures Reject Vehicle If:
(a) Parking Brake Function.
  (i) Set the parking brake firmly and check the ability of parking brake to hold the vehicle.
  (ii) All vehicles manufactured after May 23, 1970 shall have a mechanical parking brake which will hold the vehicle to the limit of traction in either direction on a 20 percent grade.
(a)
  (i) Brake fails to hold the vehicle on any grade on which it is operated.
  (ii) A ratchet-type parking brake cannot be applied to hold the vehicle on any grade on which it is operated.
(b) Linings and Drums.
  (i) If the vehicle is equipped with parking brakes which are separate from the service brakes, inspect the linings and drums in the same manner that those on the service brakes are inspected.
(b)
  (i) Parking brake drums are cracked, broken, or otherwise damaged.
  (ii) Linings are loose, worn out, or contaminated with grease, oil, or brake fluid.

H. Brake Performance Chart.

  Service Brake System Emergency
Brake
System
Column 1 2 3 4 5
  Braking force as a % 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
* 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 is effective on vehicles manufactured after July 1, 1973.
Explanation of Section H

(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 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 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 build-up 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.

I. 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.

J. Brake Testing Machines.

(1) These types of brakes 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 these machines will occasionally exhibit much higher coefficients of friction than is possible on the highway. Excessive braking should therefore 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.

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

(1) It shall measure 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 shall be 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.

L. 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.

Figure 16, TIRE CONSTRUCTION.

Figure 17, TIRE WEAR.