Chapter 99 - Drum Brakes

Question 1

The loss of stopping power that occurs when excessive heat reduces the friction between the brake shoe/pad and friction surface

Answer 1

Brake Fade

Question 2

Occurs when the brake drum gets so hot it expands away from the brake linings. Causes brake pedal to drop toward floor as additional fluid gets into hydraulic system

Answer 2

Mechanical Fade

Question 3

Occurs when friction coefficient of brake lining material drops because of intense heat making it “slippery”. Pedal becomes hard and there is a noticeable loss of braking power

Answer 3

Lining Fade

Question 4

Occurs under extended hard braking from high speeds where a thin layer of hot gases/dust particles build up between shoe linings and drum, acting as a lubricant. Pedal becomes hard and increased force is needed to apply appropriate stopping power

Answer 4

Gas Fade

Question 5

Occurs when moisture is trapped between the shoes and drum, acting as a lubricant. Lowers brake efficiency until friction creates enough heat to evaporate the water

Answer 5

Water Fade

Question 6

Occurs when friction assemblies of opposite sides of vehicle have different amounts of stopping power, caused by component failures, fade, mis-adjustment, etc.

Answer 6

Brake Pull

Question 7

Foundation of brake drum that mounts to suspension or axle housing

Answer 7

Backing Plate

Question 8

Stamped on the backing plate to align brake shoes to the center of friction surface inside brake drum

Answer 8

Shoe Support Pads or Shoe Contact Areas

Question 9

The water barrier created when the outer lip of backing plate sits against a machined groove in the open edge of the brake drum

Answer 9

Labyrinth Seal

Question 10

Prevents brake shoes from rotating with the drum when brakes are applied

Answer 10

Shoe Anchors

Question 11

Curved metal piece on the outer portion of brake shoe that supports the friction material

Answer 11

Lining Table, Shoe Rim, or Platform

Question 12

Small V- or U-shaped notches on ends of lining table that rest against support pads

Answer 12

Nibs

Question 13

Metal piece of brake shoe welded under the lining table that actually actuates the shoe when force is applied

Answer 13

Shoe Web

Question 14

Why does secondary/trailing brake shoe have more lining in a servo type brake drum?

Answer 14

Servo action causes the primary/leading shoe to hit the drum and then push the secondary shoe into the drum, since the shoe anchor is mounted on top, causing the trailing shoe to do most of the braking

Question 15

Name the two ways brake shoe lining is assembled

Answer 15

Riveting

Bonding

Question 16

Lining assembly that is reliable and operates more quietly, but can create stress cracks, has a reduced service life, and rivets can possibly damage drums if allowed to run thin

Answer 16

Riveted Linings

Question 17

Lining assembly that uses high-temperature adhesive to glue unto the shoe. Can wear closer to the platform, allowing longer service life and have less cracking issues. However, adhesive can fail to excessive heat and more prone to making noise since there is no absorption flex

Answer 17

Bonded Linings

Question 18

Retracts the shoes to unapplied position when pedal is released

Answer 18

Brake Shoe Return Springs

Question 19

Keeps shoes securely against support pad on the backing plate when brake is unapplied, preventing noise vibration and wear.

Answer 19

Brake Shoe Hold Downs

Question 20

Brake function where each brake shoe is applied individually, and the action of one shoe has no effect on the other

Answer 20

Non-servo Brake

Question 21

Explain self-energizing brake action

Answer 21

When leading shoe presses against drum at the top, and attempts to rotate with the drum. Since it is anchored and can’t rotate, the drum pulls against it “energizing” the braking force

Question 22

The most common drum brake design, where one action of one shoe plays upon the other. This makes it more powerful and equally able to hold both directions, though can lead to faster fade and is more susceptible to brake pull

Answer 22

Dual-servo Brake

Question 23

Found in dual-servo brakes, that connects the two shoes from the bottom

Answer 23

Adjusting Link or Starwheel Adjuster

Question 24

Types of automatic brake adjusters

Answer 24

Cable
Lever
Link

Question 25

The part of a self adjusting drum brake that engages and turns the starwheel

Answer 25

Pawl

Question 26

Prevents the pawl from overadjusting

Answer 26

Over-travel Spring