FAULT DIAGNOSIS Air/Hydraulic system

BRAKES
Fault Diagnosis
MA055
Page's 1-3

 

LOW BRAKE EFFICIENCY

1. Brakes not adjusting.
Check operation.

2. Air in hydraulic system.
Check fluid level in master cylinder.
Bleed brakes. Check hydraulic system for loss.

3. Load sensing valve faulty, or incorrectly set
Test valve. Adjust if necessary.

4- Brake linings worn.
Renew brake linings. Adjust brakes.

5- Oil or grease on linings or drums.
Renew linings. Renew hub oil seals and/or
wheel cylinder rubbers.


6. Linings or drums glazed.
Deglaze linings and drums. Check that
correct linings are being used

7.Low air pressure.
Insert test gauges into service reservoirs.
If low pressure is confirmed, checkcompressor, governor valve
and quadruplecharge protection valve.

BRAKES PULL TO ONE SIDE

1. Incorrect tyre pressures.
Inflate tyres to correct pressure.

2. Tyres not paired.
Check for similar tread depth and pattern
of tyres on each axle.

3. Suspension or steering fault
Check road springs, dampers and steering angles.

4. Oil or grease on brake linings.
Renew linings - (both sides) and hub oil
seal and/or wheel cylinder rubbers.


5. Brake shoes wrongly fitted primary/secondary interchanged, or shoe reversed.
Fit shoes correctly on backplate, with correct lining.

6. Backplate loose.
Tighten backplate bolts.

7. Wheel cylinder faulty (on opposite side to brake pull).
Renew or overhaul wheel cylinder.

8. Flexible hose blocked (on opposite side to brake pull).
Renew flexible hose.


BRAKES GRABBING
May be evident at low speed, when moderate pressure on the pedal results in the brake of one or more wheels sud­denly jamming on.

1. Brake shoes wrongly fitted -
primary/Secondary interchanged or shoes reversed.
Refit shoes correctly, with correct linings.

2. Wrong type of lining fitted.
Fit correct lining.

3. Brake drum oval.
Renew brake drum

4. Brake shoe return spring(s) broken/displaced.
Fit new shoe return springs.

5. Back plate loose.
Tighten backplate bolts.

6. Oil or grease on linings or drums.
Renew linings. Renew hub oil seal/or
wheel cylinder rubbers.

7. Hub bearings loose.
This will allow the drum to tilt in relation tothe shoes.
Adjust the hub bearings.

8. Brake drum tilted on hub.
Clean the hub flange and brake drum face.
Refit the drum square, and tighten the nuts
evenly.


BRAKES APPLY SLOWLY

1. Brakes not adjusting.
Check operation.

2. Low air pressure.
Insert test gauges into service reservoirs.
If low pressure is confirmed, check com­pressor,
governor valve and quadruple charge protection valve.

3. Excessive air leak with brakes applied
.Check and correct

4. Restriction in hydraulic line or flexible hose.
Examine hydraulic lines for kinks and
damage. Check lines and hoses for restriction.


BRAKES RELEASE SLOWLY

1. Foot control valve not exhausting freely
Test foot control valve.

2. Restriction in air lines
Examine air lines for kinks and restrictions. Release a hydraulic connection at a wheel cylinder.
If the brakes on that axle release quickly, the fault is in the hydraulic lines, master cylinder or actuator.

3. Restriction in hydraulic lines or flexible noses
Examine hydraulic lines and flexible hoses for restriction.

4. Wheel cylinder rubbers swollen.
If brakes do not release quickly when hydraulic connection is released, the fault is within the brake unit.
Examine wheel cylinder rubbers, renew if necessary, flush the hydraulic system and renew all rubbers.

5 .Brake shoe return springs broken or incorectly fitted.
Examine springs, refit or renew.

6.Master cylinder pistons sticking orseals swollen.
Release the hydraulic connections at master cylinder- If brakes release quickly
the fault is in the master cylinder or actuator. Overhaul as necessary. If seals are
swollen, flush the hydraulic system and renew all rubbers.

7.Tandem actuator pistons sticking,
Overhaul actuator.


BRAKES CHATTER

1. Brakes not adjusting.
Check operation.

2. Hub bearings loose.
Adjust hub bearings.

3. Brake drum oval.
Renew brake drum.

4. Brake drum tilted on hub flange.
Clean the hub flange and face of brake
drum. Refit the drum and tighten the boltsevenly.

5. Oil or grease on linings.
Renew linings. Renew hub oil seal and/or
wheel cylinder rubbers.


BRAKES SOUEAL

1. Dust or dirt in brake drum.
Clean out the brake assemblies.

2. Oil or grease on drum or lining.
Renew linings. Renew hub oil seal and/or
wheel cylinder rubbers.

3. Foreign material embedded in brake lining
Renew linings.

4. Brake back plate loose.
Tighten back plate securing bolts.


5. Wheel cylinder or brake adjuster loose.
Tighten the securing bolts.

6. Brake lining loose on brake shoe.
Renew lining and shoe assembly.

7. Bent or distorted brake shoes or back plate.
Renew damaged parts.


BRAKES FADE

1. Brakes not adjusting.
Check operation.

2. Incorrect brake lining fitted, or primary.secondary shoes inter­changed.
Check that brake shoes are fitted correctly,and with the correct linings.

3. Excessive air leak at actuator, or between fo.ot control valve and actuator.
Test for air leaks with brakes applied.

4. Brake drums ground excessively.
Renew brake drums.


BRAKE BINDING - ONE WHEEL

1. Brake over-adjusted.
Adjust brake.

2. Brake shoes tight/seized on backplate.
Lubricate and refit brake shoes.

3. Brake shoe return spring broken.
Renew spring.

4. Brake shoe distorted.
Renew brake shoe.

5. Wheel cylinder rubbers swollen.
Renew rubbers, flush hydraulic system and
renew all rubbers.

6. Flexible hose blocked (front only).
Release hydraulic connection at wheel
cylinder. If brake releases, fault is in hose
or hydraulic line. Renew hose.

7. Obstruction in hydraulic line.
Examine hydraulic line for kinks and
restrictions.


BRAKES BINDING - ALL WHEELS

1. Foot control valve not fully exhausting
Test foot control valve.

2. Master cylinder pistons sticking or seals swollen.
Overhaul master cylinder. If seals are swollen, flush the hydraulic system and renew all rubbers.

3. Incorrect clearance between master cylinder and actuator.
Check and if necessary adjust the clearance.

4. Tandem actuator pistons sticking.
Overhaul the actuator.

PARK BRAKE NOT APPLYING

1. Quick release valve not exhausting.
Test the quick release valve.

2. Hand control valve not exhausting.
Test the hand control valve.

3. Compensator linkage incorrectly adjusted.
Check and adjust the compensator linkage.

4. Wind-off mechanism of spring brake actuator not fully released.
check wind-off mechanism.

PARK BRAKE NOT RELEASING

1. Hand control valve faulty.
Test the hand control valve.

2. Excessive air leak in air line, hand control valve to spring brake actuator.
Test for air leaks with hand control valve in OFF position.

3. Excessive air leak in park brake circuit.
Test for air leak.

4. Piston sticking or seized in spring brake actuator.
Overhaul spring brake actuator.

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