Notice: When replacing tubing, make sure that the tubing is free of burrs, cuttings, and dirt. While wearing safety glasses, use compressed air to blow out contaminants. Contaminants can destroy the air brake valve sealants.

The air lines deliver compressed air throughout the vehicle. The air lines are made from copper and nylon tubing.

Copper air lines consist of compression fittings with a diameter dimension of 19 mm (3/4 in).

Nylon air lines consist of push-in fittings in the following diameter dimensions:

The nylon air lines are color coded for system identification in the following ways:

Nylon Air Lines

Notice: When replacing air lines connected to the push-in type fittings, be certain that the nylon air line is pushed-in and seated in the fitting. Install the tube into the fitting until no tube color is visible between the gauge band and the fitting. The air line may blow out if the tube is not properly seated in the fitting.

Notice: Nylon air line should be used to replace existing nylon lines only. Do not route nylon air lines in areas where temperatures could exceed 93°C (200°F). Damage to the nylon lines could occur.

All vehicles equipped with air brakes use a special push-in type fitting. These fittings are serviced as an assembly and should not be taken apart.

Flexible Hoses

Flexible hoses are used at the air brake chambers. These hoses connect the frame and axles with the trailer connections. Check the hoses for the following conditions:

Replace the hoses as necessary.

Trailer and Brake Couplings

Vehicles equipped for trailer hauling have two flexible air lines that connect the truck or tractor and the trailer brake systems. One is the SERVICE air line and the other is the EMERGENCY air line. The EMERGENCY air line supplies constant air pressure to the trailer air system. The SERVICE air line delivers air to the trailer when braking is desired. Use either the foot brake pedal or the trailer brake control in order to apply the trailer brakes.

The flexible nylon air lines connect to the trailer through the couplings. When the couplings are connected, the pressure on two rubber gaskets makes an air-tight seal. Replace the rubber gaskets every 6 months. Uunder severe operating conditions, replace the gaskets more frequently.

The emergency coupling is located on the right side of the trailer air brake coupling hose bracket. This bracket is mounted on the cab and is tagged EMERGENCY. The service air line is located on the left side and is tagged SERVICE. When coupling the tractor and the trailer, connect the air lines properly. The corresponding couplings on the trailer are also tagged SERVICE and EMERGENCY.

Supporting Components

Maintain the following parts:

Proper maintenance of these parts will prevent the following conditions:

Check the air line routing and the support components regularly. Do not route the nylon lines near high heat sources such as the exhaust system.

Tabbed air line support brackets are used at some locations. A tab is positioned in a hole in the frame and retained with a single nut and bolt. The tab prevents the bracket from moving.

Use clamps on these brackets for holding bulky bundles of air lines and power cables. Verify that all clamps and brackets are be in place. Tighten all clamps and brackets securely.

The air line supports brace other components. Firmly mount the support in position. Do not allow the air lines to rub on the vehicle components.

The clamps and the band ties support and protect the air lines. Use the band ties in order to hold clusters of air lines and cables, when the use of clamps, brackets, or supports is not possible.

Heat Shields and Grommets

Grommets are used when air lines pass through frame members or sheet metal. The grommets prevent wear and cuts on the air lines. Check the grommets each time brake service is required. Components must be in good condition and must be mounted correctly. The grommets should not be torn or bent. Replace all missing or damaged grommets.

In order to protect the air lines from heat, reinstall any heat shields which you removed during service.

Notice: When replacing air lines connected to the push-in type fittings, be certain that the nylon air line is pushed-in and seated in the fitting. Install the tube into the fitting until no tube color is visible between the gauge band and the fitting. The air line may blow out if the tube is not properly seated in the fitting.

Notice: Nylon air line should be used to replace existing nylon lines only. Do not route nylon air lines in areas where temperatures could exceed 93°C (200°F). Damage to the nylon lines could occur.

All vehicles equipped with air brakes use a special push-in type fitting. These fittings are serviced as an assembly and should not be taken apart.