Braking Basics

A running back darts down the football field deftly dodging and spinning his way past his opponents. He stops and turns on a dime. Would you say your bus can do the same? Or would you equate your bus more with the substantial, weighty and strong linebacker?

Buses are not loved because of their speed and agility, but more for their size and strength. Unlike a linebacker, though, buses don't have the luxury of crashing to a stop. When it comes to safely stopping a bus, you as the operator need to be acutely aware of the additional time and space needed. Many bus owners have employed the use of auxiliary braking, like that used on commercial trucks, to get additional stopping power and control.

There are many factors involved in how quickly a bus can make a complete stop. Size and weight are the biggest considerations, but tires, brake shoes, and type of engine also play a role in a bus's stopping capability. The size of tires can make a significant difference in stopping distance. Narrow tires don't offer as much surface contact with the highway, resulting in less braking efficiency. The size of the brake shoe or brake pads also plays an important role, as does the size of the drum or braking surface that contains the discs on disc brakes. The type of engine your vehicle has will also make a difference. A diesel engine has less slowdown capability than a gasoline engine because it doesn't have as much backpressure.

It is recommended that buses maintain at least six to eight seconds' distance from the vehicle in front of them. To judge this, watch when the vehicle in front of you passes a sign or a mile-marker and count the seconds until your front bumper passes that same landmark. Following too closely jeopardizes your safety because you're forced to focus all your attention on the vehicle in front of you and may be unaware of situations arising elsewhere. Ask yourself the following questions to determine if you're maintaining a safe following distance.

Answering "no" to any of these questions is an indicator that you're following too closely.

Covering the brakes is a procedure taught in the Motorcycle Safety Foundation defensive driving course. When you approach a situation that makes you uneasy, place your foot over the brake pedal without actually touching it. This reduces reaction time if your hunch proves to be correct and you need to quickly apply the brakes.

Because of their design, diesel engines have very little compression of backpressure to assist in stopping. There are several types of auxiliary braking devices available for diesel powered engines, the most popular being the exhaust brake, the engine brake, the transmission brake or retarder, and the driveline retarder. If you'll be driving in hilly terrain with steep declines, it's essential to install some form of braking assistance.

Sometimes called a retarder or extarder, the exhaust brake is normally on diesel-engine motorhomes or buses. This quiet braking aid activates a shutter valve in the exhaust system just behind the turbo charger. The closed valve causes a buildup of pressure in the exhaust system that passes back through the turbo and the valves and into the combustion chamber of the cylinder. The pressure buildup there creates braking horsepower used to slow the vehicle down. With a transmission that offers the same type of direct interface, the system is quite efficient because the same horsepower used to keep the vehicle in motion can help slow it down. The maximum efficiency is reached at the maximum engine RPMs for which the exhaust brake is rated. It's also important to note that if this braking device isn't used frequently, the air cylinder shaft can freeze up, making the device inoperable.

Referred to as the Jake brake, the engine brake is used on the larger diesel engines commonly found in bus conversions. The nickname refers to Jacobs, one of the major providers of this type of brake for many years. The brake is more expensive and cannot be used on every engine because of limited space. A Jake brake requires higher valve covers.

An efficient means of slowing a vehicle down, the transmission retarder utilizes the transmission fluid to create backpressure to assist the bus in slowing. Backpressure can be applied in one of two ways. Some vehicles have a stick mounted in the driver's area that can be moved into several positions. The further down you pull it, the more braking action is applied. You must manually downshift your transmission to help this device operate more efficiently. If you don't and instead rely only on the stick, you may overheat your transmission fluid because the transmission is not turning at high RPMs and aiding your effort to slow down. The brake pedal also usually has three sensors that detect the amount brake pedal pressure being applied and engage the retarder accordingly. The transmission retarder avoids engine damage, but if the transmission fluid is overheated, major transmission damage can result.

The most efficient, but most expensive, means of slowing a vehicle is a driveline retarder. When engaged, the electromagnet around the driveshaft creates an opposing magnetic field around the driveshaft that causes the driveshaft to resist turning, thereby slowing the coach. The driveline retarder is engaged by pulling down on a stick similar to the transmission retarder.

Vehicles powered by gasoline engines have an advantage over those powered by diesel. They offer backpressure, which allows the engine to work against itself when the accelerator is released, slowing the vehicle down. However, once a large amount of weight is factored into the situation, this engine, too, has difficulty in slowing the vehicle quickly enough. There are currently two types of supplemental brakes available for gasoline-powered vehicles. One operates on a butterfly principle, very similar to the diesel-engine exhaust brake, while the other operates exactly as the driveline retarder.

Don't take chances with your ability to stop your vehicle-your safety may depend on it. Be sure to maintain a minimum following distance of six to eight seconds so you have the maximum amount of stopping time. Buses aren't as agile as automobiles and don't stop on a dime-you need all the time you can get. Supplemental braking can be helpful in decreasing your bus's stopping distance, which may be crucial to avoiding an accident. If being safe is your priority, auxiliary braking should be a consideration.