190105e Air Brake System Testing and Service

List safety precautions when working around machinery equipped with air brake systems.

• park vehicle on level surface with the wheels blocked

• always wear safety glasses when working on air brake systems

• if you must work in the engine compartment, shut off the engine whenever possible

• if you must work around a running engine, exercise extreme caution to avoid injury caused by contact with moving, rotating, leaking, heated, and electrically charged components

• vent exhaust system if running an engine indoors

• always drain the air pressure from all of the reservoirs before starting work on the system

• never disconnect or connect lines or remove components when the system is pressurized

• never adjust system pressure above manufacturer specifications

• use extreme caution when working around, removing, or replacing spring brake chambers

• understand the air brake system you are working on by referring to the manufacturer service manuals for safety precautions, correct service procedures and tools required

• avoid inhaling dust from brake lining material

When inspecting compressor mounting security, what 2 things should you look for?

• cracked or damaged mounting brackets

• loose or missing fasteners

What is the maximum belt deflection for a compressor?

½ - ¾

What would excessive oil in the reservoirs indicate?

Worn compressor piston rings and cylinders

CVIP specifies that a vehicle will fail inspection if camshaft-bushing clearance exceeds ________.

0.085” (2 mm)

At what thickness do you remove and reline brakes?

8mm (5/16”)

The angle between the slack adjuster and brake chamber pushrod when brakes are fully applied should be _________________.

Never less than 90 degrees.

What is the rule-of-thumb when it comes to pushrod travel length?

Should be as short as possible without drag between the brake linings and drum

When should the low pressure warning deactivate?

At or above 60psi

What is governor cut out pressure? Can it be adjusted?

115-135psi

Yes

What is governor cut in pressure? Can it be adjusted?

When it falls 25psi below the cut out pressure.

No - cannot be adjusted

How much psi can be lost in different truck/tractor/trailer combinations per reservoir per unit during the supply leakage test?

2 psi/reservoir/unit

• truck can only leak 2psi

• tractor with semi-trailer can lose 4psi (2 + 2)

• B train 6psi (3 units - 2 + 2 + 2)

• etc.

How much psi can be lost in different truck/tractor/trailer combinations per reservoir per unit during the service delivery leakage test?

JUST ADD 2

• truck can lose 4psi

• tractor with semi trailer can lose 6psi

• B train can lose 8psi

• etc.

What should the pushrod variation/difference on each axle be to maintain brake balance?

Should be within 1/4”

What should you do before mechanically caging a spring brake chamber?

Inspect the spring brake chamber for cracks or physical damage

Camshaft radial clearance should not exceed __________.

0.030”

Camshaft axial clearance should not exceed _______.

0.030”

How do you correct axial clearance?

Adding or removing shims between the slack adjuster and the retaining snap ring on the camshaft

When inside diameter of a brake drum is removed, what happens to the brake drum?

decreases its strength and ability to dissipate heat

A cam-operated brake is considered properly adjusted when…

• stroke of brake chamber pushrod is as short as possible without causing the brakes to drag

• the angle formed between the pushrod and slack adjuster is greater than 90 degrees when the brakes are fully applied

When measuring free stroke range, what should it fall between?

3/8-3/4”

CVIP specifications state that a vehicle could be put out a service is the brake chamber pushrod travel does not fall between

¾ ” - 1 ½ ”

Testing the supply circuit leakage in a tandem gravel truck towing a pup trailer.

The primary service reservoir pressure drops 4psi and the secondary reservoir drops 10psi.

Is this acceptable?

Primary leakage is acceptable

Secondary leakage is excessive

Testing the service delivery circuit leakage in a body-loaded truck.

Pressure drop in the primary reservoir is 6psi and pressure drop in the secondary reservoir is 2psi.

Is this acceptable?

Primary leakage is excessive

Secondary leakage is acceptable

Dented/kinked air lines in the parking/emergency brake circuit could cause the spring brakes to……?

Act sluggish when applied or released

What happens when you open the supply line of a fully charged tractor/trailer combination with the parking brakes released?

Trailer spring brakes apply

Trailer supply valve pops out between 60-20psi and shuts off air to the supply line

What must you do before you back off brakes on units that have automatic slack adjusters?

Disengage the adjustment pawl

If the angle between the brake chamber pushrod and slack adjuster is incorrect, you must?

Adjust the brake chamber clevis

Why is it important to closely watch brake adjustment following a brake reline?

Brake chamber pushrod travel will increase more rapidly than normal as the brake linings wear into the brake drums

While doing the supply circuit leakage test, how much pressure can a body loaded truck leak?

2psi per service reservoir over 2 minutes

While doing the service delivery circuit leakage test, how much pressure is a tractor with a single trailer allowed to leak?

6psi per service reservoir over 2 minutes

While performing the automatic emergency brake circuit operation test, the secondary tank is drained fully. How much pressure will the primary and supply reservoir have?

primary reservoir should be full

supply reservoir will be at 0

With the primary reservoir fully charged and no air in the secondary reservoir, the parking brakes will _________ and the rear service brakes will ____________.

The parking brakes will not apply

The rear service brakes will be functional

With the secondary reservoir fully charged and no air in the primary reservoir, the parking brakes will __________ and the rear service brakes will _____________.

The parking brakes will not apply

The rear service brakes will be function

At what pressure will the park control button automatically pop out at?

35-45psi

Opening the supply line gladhand of a fully charged tractor/trailer combination with the parking brakes released will result in the trailer spring brakes to ____________ and the tractor spring brakes to _____________.

Trailer spring brakes will apply

Tractor spring brakes will remain released

How can you correct the angle between the brake chamber pushrod and slack adjuster when it is less than 90?

• adjusting the brakes correctly

• cutting the brake chamber pushrod correctly

When adjusting a manual slack adjuster, how much do you back off after the shoes contact the drum?

¼ turn

When adjusting an automatic slack adjuster, how much do you back off after the shoes contact the drum?

½ turn

When adjusting the disc brake assembly, the technician should tighten the adjuster until the pads contact the rotor and back it off ___________.

3 clicks