Hydraulic Brake System Drum and Disc 190103b

Question 1

1. Brake drums used on medium duty trucks are usually made from the following
material.
a) brass/copper compounds
b) steel
c) aluminum
d) cast iron or centrefuse

Answer 1

d) cast iron or centrefuse

Question 2

2. List three (3) functions of the drum brake backing plate.

Answer 2

a) Mounting points for: the anchor(s); the wheel cylinder(s).
b) Inspection holes for lining-to-drum clearance.
c) Service access holes for brake adjustment; brake bleeder screw(s).

Question 3

3. Brake shoe assemblies could be classed as servo acting or non-servo acting. Explain
   the differences.

Answer 3

Servo action occurs when one shoe is positioned so it can move the other shoe during
brake application. Non-servo action means both brake shoes act independently of
each other.

Question 4

4. Explain the purpose of brake shoe return springs.

Answer 4

Returns brake shoes to released position. Prevents brake drag. Indirectly forces brake
fluid back to the master cylinder.

Question 5

5. List two (2) functions of a disc brake caliper.

Answer 5

a) Provides cylinder bore(s) for caliper piston(s).

b) Holds inner and outer disc brake pads.

Question 6

6. Disc brake pad lining material is generally described as:

Answer 6

a) non-asbestos organic (NAO)

b) semi-metallic

Question 7

7. Explain the main purpose of vented disc brake rotors.

Answer 7

Vents provide increased cooling air flow during vehicle operation. This helps to
dissipate rotor heat faster.

Question 8

8. Disc brakes have both servo and self-energizing action.
   a) true
   b) false

Answer 8

b) false; Discs brakes have neither. They rely on a clamping force.

Question 9

9. Explain why master cylinders generally have two separate reservoirs.

Answer 9

Safety is the prime reason. Two independent systems exist. Failure in one system
does not affect the other system.

Question 10

10. The master cylinder has two small ports leading into the cylinder bore from each
    reservoir. Name, and explain the purpose(s) of the smallest port.

Answer 10

Compensating port. Allows brake fluid into the cylinder bore as the brakes are being

released. Allows heated brake fluid to expand into the reservoir to prevent brake
drag. Allows cooled fluid to return to the cylinder bore.

Question 11

11. A horizontally mounted master cylinder has a primary and a secondary piston. The
    primary piston is the first one activated by the brake pedal pushrod.
    a) true
    b) false

Answer 11

a) true

Question 12

12. Explain how the secondary piston in the master cylinder is moved during normal
    braking operation.

Answer 12

The primary piston moves; the compensating port is closed; brake fluid is trapped
between the primary and secondary piston; the trapped fluid moves the secondary
piston.

Question 13

13. Double flares and ISO flares are the two types of flares used on steel brake tubing.
    a) true
    b) false

Answer 13

A. True

Question 14

14. Steel tubing with double flares can be used with fittings that are designed for ISO
    flares.
    a) true
    b) false

Answer 14

. b) false; Double flares and fittings must never be interchanged with ISO flares
and fittings.

Question 15

15. Explain why flexible hoses are used as brake lines.

Answer 15

To prevent line breakage as components move.

Question 16

16. To protect brake line fittings from damage the following tools should be used.
    a) small pipe wrenches
    b) open end wrenches
    c) line/flare nut wrenches
    d) box end wrenches

Answer 16

c) Line/Flare nut wrenches.

Question 17

1 7. Pressurized brake fluid moves the piston seal and the piston in a drum brake wheel
cylinder.
a) true
b) false

Answer 17

A. True

Question 18

18. Pressurized brake fluid moves the piston seal and the piston in a disc brake caliper.
    a) true
    b) false

Answer 18

b) false; Fluid moves piston only.

Question 19

19. Wheel cylinders are mounted on backing plates. Calipers are mounted on anchor
    plates.
    a) true
    b) false

Answer 19

A. True

Question 20

20. Explain the purpose of the outermost seals or boots used on wheel cylinders and
    caliper pistons.

Answer 20

Prevents dirt, water or lining dust from damaging or contaminating the pistons, the
cylinder bores or the brake fluid.

Question 21

21. After brake pedal release, caliper pistons return by piston seal movement. Wheel
    cylinder pistons return due to the action of the brake shoe return springs.
    a) true
    b) false

Answer 21

A. True

Question 22

22. Brake systems may include a residual check valve. Explain the function of this type
    of valve.

Answer 22

Maintains a very small amount of line pressure. This helps prevent air seepage past
piston seals, yet does not allow brake drag.

Question 23

23. Explain the function of a metering valve.

Answer 23

Used in disc/drum brake system. Prevents disc brakes from applying until line
pressure in drum brake system overcomes brake shoe return spring tension.

Question 24

24. Explain the function of a proportioning valve.

Answer 24

Helps prevent rear wheel lock-up by restricting fluid pressure build-up to the rear
brakes, under heavy braking application.

Question 25

25. Explain the function of a pressure differential valve.

Answer 25

Activates brake warning or brake failure light on the dash when fluid pressure is lost
in one brake system. Can be used to indicate emergency brake application.