190105f Air Antilock Brake System Fundamentals

2 advantages of antilock brakes

• provides directional stability and control

• decreased stopping distances

Braking is most effective when the rotation of the wheel and tired is slowed ______________.

Without overcoming the friction between the tire and the road

How do antilock brakes slow the rotation of the wheel?

Application pressure is modulated

Antilock brake systems can modulate brake application pressure up to _________ times per second

100

What is the purpose of the tone ring?

Induces electrical pulses in the speed sensor

How does a speed sensor submit signals to the ECU?

produces a voltage signal that is proportional to wheel speed

What are the functions of the ECU?

• analyzes and processes the signal from the speed sensors

• controls the operation of brake modulators

• generates diagnostic information for system malfunctions

What are the two reasons the ABS indicator will come on?

• start up

• antilock system failure

What state are the solenoids in during normal braking?

They are both de-energized

When the ECU determines that a wheel is going to lock, what happens with the solenoids?

It energizes (activates) both solenoids

What 3 stages do the solenoids and diaphragms work together to perform?

First - exhaust

Second - hold

Third - reapply

If the antilock system fails during vehicle operation, the standard brake system will _____________.

Function normally

Describe what 4S/4M means.

• 4 sensors and 4 modulators

• on tandem drive axles there is one sensor and modulator per side (controls both of the brake chambers on that side)

Describe what 2S/2M means.

• 2 sensors and 2 modulators

Where are tone rings most commonly mounted?

Wheel hubs

What should you do with the ECU if arc welding must be performed on the vehicle?

Unplug or disconnect it

How do you correctly install a speed sensor?

Installation is complete when the sensor is touching the tone wheel

Most antilock systems specify that all tire sizes must be kept within how much of each other?

3/4”

List the 5 basic components of the antilock system

• ECU

• speed sensors

• ABS indicator lamp

• tone ring

• pressure modulator valves

A modulator valve is in the air lines to each front wheel and to the right driving tandems and the left driving tandems. What type of ABS system is this?

4S/4M

On a tandem drive axle truck chassis with one modulator valve for each side, how many brake chambers does the modulator valve control?

Two brake chambers