Each year the Commercial Vehicle Safety Alliance's “Roadcheck” on-road safety inspection blitz finds a high number of brake defects on trucks. Are your maintenance practices better? Photo: Commercial Vehicle Safety Alliance
By Paul Abelson
Whether it happens in the yard at 3 mph or going down a mountain pass at 60 mph, the feeling of panic when your brakes fail is immediate and often overwhelming.
Fortunately, complete brake failure is rare. Most drivers go through their entire careers without experiencing it, although I'd be willing to bet that just as many have firsthand knowledge of brake fade.
Brake fade occurs when the drum heats up from excessive friction and expands. Organic materials in the brake friction linings vaporize, filling the void between drum and lining with gases. The gases reduce friction between drum and lining. When this happens as you're going downhill, your only option may be to use an escape ramp or hope there are no deep ditches along the roadside.
Disc brakes, now standard on most light- and medium-duty trucks, overcome this by providing a ready path for the volatiles to escape as the calipers clamp harder. Unlike brake drums that expand away from the linings, discs actually expand into the calipers, forcing out the gases.
To avoid brake fade, let your engine or retarder do the braking for you. A good Jake Brake, or other compression brake, that's well set up and maintained on your diesel engine can generate about as much retarding horsepower as the engine develops regular horsepower. Having one can be a lifesaver. Many medium-duty trucks use exhaust brakes that increase back pressure.
I remember going down a long, 3% grade with just a few pounds shy of 80,000 behind me. With no application of the brake pedal, the Jake held truck speed constant for a mile and a half. Gearing is still important; stay in the right gear as you go over the crest. Unless you have an automated or automatic transmission, don't shift gears if you're picking up speed downhill. Stab the brakes hard to snub your speed, and then back off to let the brakes cool. Don't ride the pedal, or you'll soon run out of brakes completely.
Even braking force on all wheels is also necessary for safe operations. If one brake is too tight, it will grab first. More often, though, one or two brakes are too loose and won't do their fair share of work. That puts extra strain on the others, causing them to fade prematurely. Keep brakes in balance by adjusting them within ¼ inch or less of each other.PARTS AND MAINTENANCE
When something breaks, if you'll pardon the pun, it usually happens to only one brake at a time. That leaves you five others if you're bobtailing and four more if you're pulling a trailer. It's rare that something will happen to the entire system as long as you do your pre-trip inspections and regular maintenance using quality parts.
Look for cracks. When individual brakes fail, it's probably due to cracked drums, worn or cracked linings, or broken shoes. Cracks in excess of 1/16 inch across the face of a brake shoe will put a vehicle out of service. So will missing portions that leave rivets exposed, or cracks of any size that extend all the way across the face.
Beware of counterfeits. Counterfeit parts have been a problem for as long as I've been in the industry. They appear most often in high-volume, frequently used parts like seals, lines, and brake linings. Jobbers think they're helping customers by offering low-price replacement parts from outside their traditional supply sources. More often than not, these are imported counterfeits that wear out quickly and may not perform safely.
Keep air brakes dry. When the days are warm and overnight temperatures drop, condensation becomes a problem. Compressed air has lots of moisture, which can condense in the air storage tanks. They must be drained regularly.
Water is incompressible and takes up the volume needed for air storage. Water in your air tanks means you may not have enough air available for more than a few applications. That's why it's important to yank those lanyards after every trip.
Don't wait for your morning pre-trip. In cold weather, the water could freeze in the tanks and crack valves, making brakes inoperative. Get the water out after each shift. Use desiccant cartridges and make sure they function.
Within the decade, we'll probably have electronics to apply air evenly to all brakes, and we may even have electric braking. But that will rely on rewriting some current regulations. Until then, we'll have to rely on our air brakes and periodic maintenance to prevent brake failure.
Most importantly, use your brakes wisely. Get into that lower gear before you descend the hill. If in doubt, stay in gear. If all else fails, turn the key and shut off the engine, and cross your fingers.
— Paul Abelson (firstname.lastname@example.org) is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.