When doing a brake job, do your mechanics simply rip the old shoes off and slap on relined ones? Big mistake.
Why? Because what stops a truck is a brake system. Individual parts within that system depend on each other to perform properly. So, scrutinizing all components for abnormalities when performing a brake reline helps explain premature lining wear and performance problems, and can head off future troubles.
The following recommended brake inspection tips are from CCJ’s Air Brake book and Haldex Brake Systems, Kansas City, Mo.:
Look right away for grease or oil on the linings. These should definitely not be reused. Grease or oil migrating to the friction material will cause the lining to glaze and either not perform in balance with the other wheels or fail completely.
Next, look for heat-checking in the linings. If you see signs of heat-checking on some linings and not others, you’ll know that the wheels are not braking evenly.
If you find heat-checking on all the linings, this could indicate that the wrong lining is being used for that particular application, that the vehicle is being overloaded or a combination of both.
Look for uneven or tapered wear, both radially (around the shoe) and axially (across the width of the lining). Radial tapered wear often indicates a weak return spring, a worn S-cam bushing or an out-of-arc shoe.
Also, look for uneven or tapered wear, both radially (around the shoe) and axially (across the width of the lining). Radial tapered wear often indicates a weak return spring, a worn S-cam bushing or an out-of-arc shoe.
Axial tapered wear can be the work of a “bell-mouthed” drum. It can also be the result of worn anchor pins, holes or bushings, or worn outer S-cam bushings. These allow applied force to push shoes to one side.
Inspection of drum surfaces is also important. Look closely at each drum for signs of uneven wear, scoring, glazing or heat-checking. Heat checks, cracks and blue spots indicate excessive heat. Mild scoring (less than .010 inch) and light heat checking are acceptable. Pronounced or long (over 1 inch) cracks or heat checks point to an overload or imbalance condition, and the drum should be discarded.
Next, inspect the S-cam for wear at the bushing, at the head and around the spline. A wheel with a worn S-cam or bushing is probably not doing its share of the braking and needs adjustment, repair or replacement.
Look closely at S-cam rollers. Flat spots and pitting cause brake noise, and make brakes grabby and slow to release.
Be sure to check the brake adjuster for proper settings and operation. Also inspect clevis pins and brake adjuster bushings for signs of wear. If there’s wear of over .030, replace both. Never mix automatic brake adjusters with manual brake adjusters. And, never mix different makes of automatic brake adjusters on the same axle.
Compare the amount of wear on the front axle linings against the wear on the rear axle linings on both trucks and trailers. If the wear is unequal, you’ll know that there’s an air timing imbalance or a mix of different rated friction materials. Also, you’ll want to check for inconsistent use of elbows in air lines. Keep in mind that a 90-degree elbow is the equivalent of 7 feet of extra hose.
Finally, inspect spiders. Pay close attention to the anchor pin hole area and look for squareness. If the assembly isn’t square, uneven wear will result.
When you put everything back together, you want the system to be as close as possible to original condition. The results will be good, balanced performance and lining life that rivals original equipment.
