Inspecting Air Brake Components
Drivers of vehicles with air brakes must be able to inspect and identify defects in the air brake system components according to the Ontario Highway Traffic Act and regulations. This chapter explains how to carry out the inspection.
Inspecting the brake system
Completing an inspection of an air brake system mainly involves looking to see that each brake component is free from apparent defects or problems and that there is no evidence of any abnormality. This type of inspection is limited to those components that are visible to the driver.
Some defects are more difficult to detect than others. To carry out inspections effectively, drivers must be aware of the possible defective conditions that can exist and the evidence of their presence.
Important: Proper safety equipment may be required while conducting inspection i.e. safety glasses, steel toe shoes and bump caps
Inspecting foundation brake components
Begin by inspecting the foundation brake components for damage caused by debris, component failure or deterioration. Drivers are expected to identify brake components that are damaged, missing or malfunctioning. To detect these defects, you must be familiar with the normal appearance of the foundation brake components and the signs of present or impending defects.
Check brake-lining to drum contact
For the brakes to work, the brake-shoe lining must be pressed against the brake drum when brakes are applied, and be out of contact with the drum when brakes are released. Lining that does not contact the drum when the brakes are applied indicates a malfunctioning brake. (See Diagram 9-1.)
Check brake-lining conditions
Brake-lining is the friction material that is fastened to the metal brake shoe. For the brake to work properly, the lining must be in good condition and remain securely attached to the shoe. Brake-lining that is noticeably cracked, loose or missing is defective.
Check brake-lining contamination
Within the wheel assembly are components that require lubrication. When problems develop within the wheel, some of the lubricant may escape and come into contact with the brake-lining. When grease or oil is present on the brake-lining, abnormal brake behaviour will result. brake-lining that is contaminated with grease or oil is defective.
Check brake-lining thickness
Brake-linings are manufactured to standard dimensions that allow a considerable portion of the lining to wear before replacement is needed. When the lining is worn too thin, there is an increased danger of brake failure and damage to other components. Lining that is less than the prescribed minimum thickness is defective.
An inspection of the foundation brake components includes checking for the following defects:
- brake-shoe lining not contacting the brake drum
- damaged, missing or malfunctioning foundation brake components
- cracked, loose, missing or contaminated brake-lining, improper drum contact or lining thickness that is less than required
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with a foundation brake defect on any road or highway.
Inspecting air brake chambers
The size of an air brake chamber is based on the area of the chamber diaphragm in square inches. The brake on each end of an axle should have the same size air brake chamber to ensure brake forces are balanced. This is even more important for steering axles where brake imbalance can affect the steering. Air brake chambers from different manufacturers may look different even if they are the same size.
Air brake chambers must be inspected for leaks when air pressure is applied to the chamber. This means inspecting the chamber when the spring brakes are released and the service brakes are applied. Air brake chamber air leaks can usually be detected audibly.
Air brake chambers may have vent holes that are visible. These are manufactured holes and are not a concern. Holes or cracks that are caused by impact or other forms of damage mean the air brake chamber is defective.
The brake chamber is connected to the brake assembly by a pushrod, yoke, clevis pin, slack adjuster and camshaft. Slack adjusters act as levers that increase the force of the air brake chambers. Their effective length is critical. Most slack adjusters are designed with two or three holes for attachment of the pushrod. Attaching the slack adjuster using the incorrect hole changes the slack adjuster’s effective length. The slack adjuster’s effective length is the distance between the centre of the camshaft and the clevis pin. To ensure balanced braking, slack adjusters on each side of an axle should be the same effective lengths. Therefore, when slack adjusters have multiple holes, the pushrods on each side of the axle are usually attached using the same hole.
Some models of slack adjusters use varying patterns of holes that can result in a different appearance on each end of an axle, even when they are correctly attached. The distance between the center of the camshaft and the clevis pin must always be the same on each end of a steering axle.
An inspection of a vehicle’s air brake chambers includes checking for the following defects:
- audible air leaks
- cracks and non-manufactured holes
- mismatched air brake chamber size on a steering axle
- mismatched slack adjuster effective length on a steering axle
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with an air brake chamber defect on any road or highway.
Inspecting brake drums and rotors
Wheels, dust shields and other parts of the vehicle may obstruct your view of the brake drums and rotors. Drivers must inspect drums and rotors for damage and signs of cracks or breaks. There is often a noticeable change in the behaviour of brakes with drums or rotors that are defective, cracked or broken.
An inspection of a vehicle’s brake drums and rotors includes checking for the following defect:
- cracked or broken brake drums or rotors
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with a brake drum or rotor defect on any road or highway.
Inspecting brake hoses and tubes
A variety of hoses and tubes make up the air lines used in an air brake system. Some of these air lines are positioned against the vehicle frame and other structural parts. Others that are exposed are more likely to suffer damage.
Hoses and tubes have an inner layer to create an air-tight seal, reinforcing fabric layers to provide strength and an outer layer of plastic or rubber for protection. Some may use steel reinforcing layers. Holes or wear in an outer layer may lead to holes in the inner layers. Holes in the inner layers will produce an air leak. Damaged or worn air lines are a concern even if no leak is evident yet.
When damage extends into the reinforcing or inner layer, the air line is defective. In some cases, different colours of material are used to indicate when wear extends through a layer.
Damage or deterioration to brake hoses and tubes may be in the form of wear, cuts, abrasion and heat damage. Air leaks are usually detectable audibly; moving hoses and tubing back and forth often helps to pinpoint a leak.
Air brake systems require the use of fittings specifically designed and approved for use. Using improper fittings, or connecting or repairing air lines by improper means, is prohibited.
An inspection of the vehicle’s air lines includes checking for the following defects:
- audible air leak
- damaged or worn air lines
- improper fittings used to connect or repair an air line
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with an air line defect on any road or highway.
Inspecting air tanks
Air tanks must remain securely attached to the vehicle. Check that they are secure both by looking at them and by attempting to move them. In addition to the tanks themselves, check the security of the mounting brackets and hardware that hold the air tanks to the vehicle. Unusual movement may indicate an insecure air tank or mounting bracket.
An inspection of a vehicle’s air tanks includes checking for the following defect:
- insecurely mounted air tank
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with a defective air tank on any road or highway.
Inspecting air compressors
Air compressors must be securely mounted onto the engine, and any supports or brackets that are used must also be secure. Air compressors must always be inspected with the engine stopped. If a compressor is belt-driven, inspect the condition and tension of the drive pulleys and belt. Drive pulleys must be secure and in good condition. The belt should give slightly when firm hand pressure is applied. Excessive belt movement indicates the belt is too loose. A belt that is loose, cut or frayed is defective.
An inspection of a vehicle’s air compressor includes checking for the following defects:
- loose air compressor drive
- belt pulley
- loose, cut or frayed air compressor drive belt
- insecure air compressor mounting, bracket or fasteners
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with a defective air compressor, mounting bracket, fasteners or drive belt on any road or highway.
Key points to remember
- When inspecting the foundation brake components, the driver must check for any that are damaged, missing or malfunctioning; cracked, loose, missing or contaminated brake linings; improper drum contact; and linings that are less than the required thickness.
- When inspecting the air brake chambers, the driver must check for audible air leaks, cracks and non-manufactured holes.
- When inspecting the brake chambers on each side of a steering axle, the driver must check for mismatched slack adjusters and air brake chamber size.
- When inspecting the brake drums and rotors, the driver must check for cracked or broken drums or rotors.
- When inspecting the air brake hoses and tubes that make up the air lines, the driver must check for leaks, damage or wear, as well as improper fittings.
- When inspecting the air tanks, the driver must check for insecure mounting.
- When inspecting the air compressor, the driver must check for a loose, frayed or cut drive belt, as well as insecure mounting bracket or fasteners.