190105b Air Brake System Mechanical Components

Properly adjusted cam-operated foundation brakes ensure what?

The brake linings are as close to the brake drum as possible without dragging when the brakes are released

Where are the brake shoe rollers when foundation brakes are in the released position?

In contact with the low cam area

The linear motion of the brake chamber pushrod is converted to twisting force at the brake camshaft by the ______.

Slack adjuster

What are the 3 things brake drums must be able to do?

1. be able to resist distortion

2. be able to withstand high temperatures

3. provide an acceptable braking surface

Does brake drum thickness affect brake operation? If so, why?

Yes, it affects the drum’s ability to dissipate heat. The thinner the drum becomes, the more susceptible it is to overheating, cracking, and failure.

What is another name (and definition of) for cam-operated foundation brakes?

Non-servo brakes - one end of the shoe is mounted to a stationary pivot pin

Brake lining edge code identified the lining by 3 things…

1. manufacturer’s initials

2. part number

3. friction code (normal coefficient and hot coefficient)

What happens when using a brake lining with a GAWR that is too low?

Brake fade

What transfers torque from the brake shoes to the axle housing?

Brake spider

Where and why are flat brake cams used?

Typically used in steer axle foundation brakes because they have a slower rate of application (air reaches steer axle quicker than rear so it needed to be slowed down so all brakes are applied at the same time)

During application, the angle formed between the brake chamber pushrod and the slack adjuster arm should NEVER be…..

Less than 90 degrees (or greater than 95 degrees)

One of the most frequent causes of brake failure is _________.

Improper brake adjustment

When do automatic slack adjusters actually make the brake adjustment?

When the brakes are released

What is an advantage of air disc brakes over cam-operated drum brakes?

Are not as prone to brake fade because they are capable of dissipating more heat than drum brakes

Why should the calipers on air disc brakes be able to slide freely on the slide pins?

So that the outboard brake pad can contact the brake rotor.

How much wear (in inches) is allowed on brake drums?

.120”

What is a centerfuse cast brake drum?

A steel outer shell with a cast iron liner

What are brake blocks (linings) made of?

fibres (glass, ceramic, carbon, etc.), friction modifiers, and resin

What is the most important factors influencing the selection of brake lining material?

GAWR (Gross Axle Weight Rating)

• an indication of the lining’s ability to stop a loaded vehicle without excessive wear or overheating

What are the names for a 2 anchor pin style vs. 1 anchor pin style?

2 anchor - Meritor

1 anchor - Eaton

Where are brake shoe retaining springs and what is their purpose?

Located on the heel, holding the heel of the brake shoe against the anchor pins

Where are brake shoe return springs located and what is their purpose?

Located on the toe, holding the brake shoe rollers in contact with the S cam

Can brake camshafts be installed on either side of the vehicle/be interchanged?

No, they are oriented to left or right wheel rotation

What are 3 things the slack adjusters do?

1. convert linear motion of brake chamber into rotary motion of the camshaft

2. acts as a lever, multiplying force

3. provides a place to adjust lining to drum clearance

What is the most important reason for having a maximum diameter on a drum?

So the drum does not change shape as it heats up

Are the forward/reverse shoes different? Do they need to be installed in certain spots?

No, they are the same

How is wear between the pads and rotors corrected on a cam and lever disc brake?

the adjuster mechanism (NOT slack adjuster) rotates the threaded tubes in the bridge, causing them to move closer to the rotor