With “brakes out of adjustment” as the leading cause of Commercial Vehicle Safety Alliance (CVSA) defects, technicians should evaluate the air-braked vehicles in their fleet prior to a road trip.
CVSA (www.cvsa.org) is an international not-for-profit organization whose mission is to promote commercial motor vehicle safety and security by providing leadership to enforcement, industry and policy makers.
Articles have been written on measuring and correcting chamber stroke, as well as on defining the defects given by CVSA inspectors. Instead of repeating that information, let’s look at other brake issues that are often found in an inspection, so the fleet maintenance departments can focus on preventing them.
- Defective lining conditions. These are often seen by CVSA inspectors, so a strong preventive maintenance program is required to make sure that vehicles are ready to hit the road in top condition.
According to the CVSA’s North American Standard Out-of-Service Criteria (OOSC), the following will be scored as a defect:
- Lining cracks or voids that exceed 1/16” (1.6mm) in width observable on the edge of the lining.
- Crack that exceeds 1-1/2” (38.1mm) in length.
- Loose lining that has approximately 1/16” (1.6mm) of movement on the shoe.
- Friction surfaces of the brake drum and the brake friction are contaminated by oil or grease.
- Lining thickness less than 1/4” (6.4mm) or worn into the wear indicator, if lining is so marked, measured at the shoe center.
The OOSC are the pass-fail criteria for North American Standard Inspections. Their purpose, explains the CVSA, is to identify those violations that are an imminent hazard and which, when discovered, render the driver, vehicle and/or cargo “out of service” until such time that the condition(s) or defect(s) can be corrected or fixed.
The OOSC change and are updated annually and generally are effective April 1 of each year.
- Rust jacking. This condition is important to deal with, especially after the tough winter that most of the country experienced.
Liquid calcium chloride and magnesium chloride, along with sodium chloride (rock salt), are great for clearing ice off the roads, but they also are great at rusting a fleet’s equipment. When the “stew” of these chemicals gets between the brake lining and shoe table, rust will form.
The area likely will stay damp with these chemicals for an extended period of time. This accelerates the rust action, resulting in a “jacking” effect and cracked lining.
Because rust jacking does not go away, change the brake shoes if there are indications that the process has started.
Indicators of Trouble
Current disc brake designs cannot be measured for stroke, but there are conditions that CVSA inspectors look for. Again, referring to the OOSC:
- Missing or broken caliper, brake pad, pad-retaining components.
- Loose or missing brake chamber or caliper-mounting bolt.
- Rotor has evidence of metal-to-metal contact on the friction surface.
- Rotor has severe rusting on the rotor friction surface on either side (light rusting on the friction surface is normal).
- The friction surface of the brake rotor and the brake friction material are contaminated by oil or grease.
- Brake pad thickness less than 1/16” (1.6mm) or to wear indicator, if pad is so marked.
Unusual Defects
While there are defects that a fleet with good, competent maintenance cannot comprehend, the CVSA sees some “interesting” things and documents them. Pictures can be found in the referenced OOSC handbook.
That said, make sure your vehicles do not fail inspection due to the following:
- Loose air chamber, spider or camshaft support bracket.
- Missing brake lining – segment or entire blocks.
- Missing brake shoes or missing brake pads.
- Mismatched air chamber sizes side-to-side on an axle.
- Air chamber in wrong mounting-hole position on the chamber bracket.
- Missing clevis pin.
- Missing air chamber.
- Missing camshaft.
- Missing slack adjuster.
- Missing brake.
- Inoperative brake.
- Cracked brake drum or cracked rotor.
- Non-manufactured holes in air chambers or spring brake housing.
- Audible air leak.
Always replace brake hardware in axle sets and never a wheel-end at a time. Match the friction with the vocation for optimum life.
With a good preventive maintenance program, your fleet will sail through CVSA inspections and keep on truckin’.
John Thompson is sales manager, NAFTA, for TMD Friction (www.tmdfriction.us), a manufacturer of brake friction materials for the automotive and brake industries.
