Air Brakes Trailers

On a semi-trailer, the air brake system normally receives air from the tractor via:

A hydraulic hose The red supply (emergency) line and blue service (control) line through glad hands An electrical plug only The fifth wheel locks

The trailer supply (emergency) line is used to:

Control service brake applications only Charge the trailer reservoirs and control trailer spring brake release Control trailer lighting Vent air from the brake chambers

When the trailer supply line loses pressure suddenly (for example, line separation), the trailer brakes:

Release completely Apply automatically as spring brakes come on through the emergency relay/spring brake valve Do nothing Operate only the ABS

The service (control) line on a trailer system carries:

Reservoir supply air to charge tanks Control signal air from the tractor service valve to trailer relay valves Hydraulic fluid Only exhaust air from the chambers

Relay emergency valves (or spring brake control valves) on trailers are used to:

Operate the lights Automatically apply trailer spring brakes if supply pressure is lost and control charging of reservoirs Reduce tire wear Operate suspension air bags

Trailer reservoirs are usually mounted:

Inside the kingpin On the trailer frame where they are protected and accessible On the tractor cab Inside the tires

Shutoff cocks at the rear of a trailer are used to:

Adjust brake shoe clearance Open or close air flow to additional trailers in a multi-trailer combination Control suspension height Bleed hydraulic fluid

On converter dollies used between trailers, air brake equipment includes:

Only hand brakes Reservoirs, relay valves, spring brake chambers and glad hands similar to trailers Only spring brakes with no service brakes Hydraulic disc brakes

ABS on trailers is identified by:

An ABS lamp on the tractor dash only A yellow or amber ABS indicator lamp on the left rear of the trailer and sometimes diagnostic connectors Red reflectors only Special spring brakes

A 'no-ABS' trailer will:

Not have any brakes Still have conventional air brakes but without electronic wheel-lock control Use hydraulic braking Not be allowed on any roads

Service relay valves on trailers are located near the axles so that:

Long control lines delay brake application Short lines from the relay valves to the chambers reduce application and release time Brakes apply only when parked They can be mounted on the kingpin

The 'spring brake priority' feature in some trailer valves ensures that:

Service brakes get air before spring brakes release Trailer spring brakes release first when charging a depleted system to allow vehicle movement Only the hand valve can apply trailer brakes Only parking brakes work when fully charged

Trailer parking brakes are typically applied by:

Hydraulic pressure from the tractor Spring force in dual-chamber brake actuators when supply air is removed Electric motors Manual screw jacks on the axles

The service reservoir on a trailer is linked to the supply line through:

A direct open pipe A one-way check valve so reservoir air is retained if supply pressure drops A hand valve only The fifth wheel jaws

When coupling a trailer, one important step regarding air lines is to:

Cross the supply and service lines for better flexibility Connect the red supply line to the red glad hand and the blue service line to the blue glad hand Connect both hoses to any glad hand Connect them to the electrical plug

Spring brake chambers on trailers are usually located:

Only on the steer axle On the trailer axles, often in dual chamber units combining service and parking/emergency functions Inside the kingpin On the tractor frame

A trailer with a 'dead' or capped service line but charged supply line will:

Have no brakes at all Have parking brakes released but no normal service brake control from the tractor Operate normally Apply only the steer axle brakes

The ILM Air Brakes Trailers module expects parts technicians to:

Perform trailer road tests and inspections Identify trailer brake system layouts, valves, chambers and reservoirs when supplying parts Install kingpins and fifth wheels Program trailer ABS ECUs in the shop

Typical foundation brakes on highway trailers are:

Hydraulic drum brakes Air-operated S-cam drum or disc brakes on each wheel end Mechanical cable drum brakes Electric drum brakes only

ABS modulator valves on trailers are installed:

At the compressor outlet Near the service brake chambers to rapidly modulate pressure during ABS events Inside the tractor cab Only on steer axles

The electrical ABS power and control for the trailer usually comes through:

The red air line The 7-way (or similar) electrical connector between tractor and trailer The fifth wheel jaws A ground strap only

Trailer spring brake chambers may be labelled:

Type 9 only With service and spring brake section sizes (for example 30/30) Only by manufacturer name With tire size

Relay emergency valves often combine the functions of:

Lighting and suspension valves Service relay, emergency application and reservoir charging control Compressor and governor ABS and traction control

In a trailer air system, a breakaway cable or device may be present to:

Disconnect the fifth wheel Ensure supply line pressure is lost and spring brakes apply if the trailer separates from the tractor Shut off the engine Apply hydraulic brakes

Some trailers use 'service reservoir priority' so that:

Trailer parking brakes release before service reservoir is charged Service reservoir reaches a usable pressure before spring brakes fully release Only parking brakes operate ABS is disabled

Trailer air tanks must meet standards that require:

Lightweight plastic construction Pressure ratings, drain provisions and identification markings for inspection No drains or markings Single-port designs only

Combination vehicles with multiple trailers (road trains) require air systems designed to:

Operate only the first trailer brakes Supply all trailers with adequate pressure and response time through additional valves and reservoirs Use hydraulic boosters Eliminate the need for spring brakes

When supplying replacement glad hands for trailers, parts technicians must match:

Any general connector Service vs emergency styles, seal type, mounting and hose connection type Only colour Electrical pin layout

Dump trailers with lift axles may include air valves that:

Control cooling system operation Raise or lower axles using suspension air circuits based on load or driver control Open tailgates only Operate ABS

Trailer brake adjustment requirements are similar to tractors in that:

Linings do not wear Slack adjuster stroke must remain within specified limits for safe operation Any stroke is acceptable Only steer axles matter

A trailer equipped with disc brakes instead of S-cam drums will still:

Use air-operated actuators and similar control valves Use hydraulic fluid only Use mechanical cables Require no air lines

The term 'piggyback' in some trailer brake catalogues may refer to:

Stacked trailers for shipping Combined spring brake and service brake chamber assemblies supplied as one unit Multi-axle suspension Spare wheels carried on the frame

On some trailers, a 'service glad hand' may be mounted:

On the roof only On the front and rear so the trailer can be positioned as lead or tail in a combination Only under the floor Inside the kingpin housing

Trailer air system drains should be opened periodically to:

Increase air pressure Remove accumulated moisture and contaminants from reservoirs Fill tanks with water Check engine oil level

When ordering replacement relay or relay-emergency valves for trailers, important details include:

Paint colour and logo only Port size and location, crack pressure, mounting pattern and application type Approximate weight only Number of wheel studs

Trailer ABS fault codes and diagnostics are usually accessed:

Only at the tractor dashboard Through ABS indicator light flash codes or diagnostic connectors near the trailer ECU Through the fuel tank cap By reading tire brand

A trailer that is 'air-locked' (air trapped and not flowing correctly) after coupling may require:

Higher engine RPM only Operating the trailer supply valve off and on to fully charge and stabilize the system Removing all reservoirs Disconnecting ABS sensors