The trailer braking system is completely dependent on the satisfactory functioning of the tractor system, both for the air pressure supply and the control. Therefore it is advisable to ensure that the tractor system is working correctly before condemning the trailer braking system. For further information on brakes, refer to Bedding in the Running Gear.
Brakes inefficient
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- Brakes need adjustment, relining or lubrication.
- Brake valve output pressure, on tractor vehicle, below normal.
- Defective relay emergency valve, giving low delivery pressures.
- Low air pressure in tractor and / or trailer system.
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Brakes apply slowly
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- Brakes need adjustment, or lubricating.
- Brake valve output, on tractor vehicle below normal.
- Low air pressure in tractor and / or trailer system.
- Damaged airline or hose, restricting airflow.
- Excessive leakage when brakes applied.
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Brakes release slowly
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- Brakes need correct adjustment.
- Brakes or linkage binding requiring lubrication.
- Exhaust port or relay emergency, or quick release valves obstructed.
- Restricted hose, or damaged airline.
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Brakes not functioning
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- Cut out cock on "service" line closed.
- Service line coupling disconnected, or excessive leakage in line.
- Shut off cock on "emergency" line closed and no pressure in trailer reservoir. "Emergency" line coupling disconnected, or excessive leakage.
- Obstructed airline or hose.
- Leakage in brake operating units, or air lines.
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Brakes do not release
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- "Emergency" line coupling disconnected, or excessive leakage.
- Handbrake valve in applied position.
- Relay emergency valve in emergency position.
- Cutout cocks closed.
- Obstructed airline or hose.
- Brake assemblies binding.
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Brakes grab
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- Grease or oil on brake linings.
- Brake assemblies or linkage binding.
- Defective relay emergency valve, or brake valve.
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Uneven braking
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- Brakes need adjustment, relining or lubricating.
- Grease, or oil, on brake linings.
- Brake assembly damaged, or springs broken.
- Return spring broken in brake operating unit.
- Defecting diaphragm, or seal, in brake operating unit.
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Air leakage with brakes released
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- Relay emergency valve leaking.
- Leaking airline, or hose.
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Air leakage with brakes fully applied
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- Relay emergency valve, or tractor brake valve, leaking.
- Leaking airline or hose.
- Defective diaphragm, or seal, in brake operating unit.
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Excessive oil and water present in the system
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- Reservoirs, on tractor and trailer, not being drained often enough.
- Air compressor, on tractor, passing excessive oil.
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