Most brake experts agree that even the most complicated balance, timing and compatibility problems can be minimized by a good PM program. We’re talking about steps taken to keep brakes performing as they did when they were new, to prevent problems from occurring and to detect small problems before they become big ones. It’s some of the easiest work your shop can perform, and it has the potential to let you help customers avoid expensive inspection violations, accidents and litigation.
Routine checks: What and when
Because every customer’s operation is a little different, maintenance intervals will vary. Only experience will produce a reliable timetable for preventive brake maintenance.
Most brake manufacturers recommend a visual inspection for wear, broken parts, chafed or badly routed air lines and other obvious damage whenever any brake service is required. Generally speaking, such a check should be made at least every three months.
Whatever the interval, it’s a good idea to accompany the inspection with a thorough operational check. Look at the whole system. The best way to do that is to go from the front bumper to the taillights, making sure everything is doing what it’s supposed to.
Because air is the lifeblood of a brake system, there must be enough of it. And it must be clean. So the compressor’s as good a place as any to start your PM inspection. With the engine running at full governed rpm, air pressure should build from 85 psi to 100 psi in 25 seconds or less, with normal-size reservoirs. If it doesn’t build up in time, and the system isn’t leaking, there’s a good chance a dirty air filter is restricting the compressor intake. That’s not a catastrophe in itself, but it quickly can lead to complications.
When a compressor tries to draw air through a plugged filter, a vacuum is created during the intake stroke. That vacuum is partially relieved by oil sucked past the compressor’s piston rings.
During the compression stroke, the oil is pumped into the discharge line and gums up components downstream- especially relay valves. Periodic checking and replacement of air filters is an easy way to ward off expensive headaches.
