CDL Practice Tests For Safe Driving Page 8

Stab braking:

Use only on vehicles without anti-lock brake systems.

• Apply your brakes all the way.
• Release brakes when wheels lock up.
• As soon as the wheels start rolling, apply the brakes fully again. (It can take up to 1 second for the wheels to start rolling after you release the brakes. If you reapply the brakes before the wheels start rolling, the vehicle will not straighten out.)

Do not jam on the brakes:

Use only on vehicles without anti-lock brake systems. Emergency braking does not mean pushing down on the brake pedal as hard as you can. That will only keep the wheels locked up and cause a skid. If the wheels are skidding, you cannot control the vehicle.

Loss of hydraulic pressure:

When the system will not build up pressure, the brake pedal will feel spongy or go to the floor. Following are things you can do:

• Downshift – Putting the vehicle into a lower gear will help to slow the vehicle.
• Pump the brakes – Sometimes pumping the brake pedal will generate enough hydraulic pressure to stop the vehicle.
• Use the parking brake – The parking or emergency brake is separate from the hydraulic brake system. Therefore, it can be used to slow the vehicle. However, be sure to press the release button or pull the release lever at the same time you use the emergency brake so you can adjust the brake pressure and keep the wheels from locking up.

Find an escape route:

While slowing the vehicle, look for an escape route — an open field, side street or escape ramp. Turning uphill is a good way to slow and stop the vehicle. Make sure the vehicle does not start rolling backward after you stop. Put it in low gear, apply the parking brake and, if necessary, roll back into some obstacle that will stop the vehicle.

Brake failure on downgrades:

Going slow enough and braking properly will almost always prevent brake failure on long downgrades. Once the brakes have failed, however, look outside your vehicle for something to stop it.

Your best hope is an escape ramp. If there is one, there will be signs posted. Ramps are usually located a few miles from the top of the downgrade. Every year, hundreds of drivers avoid injury to themselves or damage to their vehicles by using escape ramps. Some escape ramps use soft gravel that resists the motion of the vehicle and brings it to a stop. Others turn uphill, using the hill to stop the vehicle and soft gravel to hold it in place.

Tire Failure —

Quickly knowing you have a tire failure will let you have more time to react. Having just a few seconds to remember what it is you are supposed to do can help you. The major signs of tire failure are:

• Sound – The loud “bang” of a blowout is an easily recognized sign. Because it can take a few seconds for your vehicle to react, you might think it was another vehicle. But any time you hear a tire blow, you are safest to assume it is yours.
• Vibration – If the vehicle thumps or vibrates heavily, it may be a sign that one of the tires has gone flat. With a rear tire, that may be the only sign you get.
• Feel – If the steering feels “heavy,” it is probably a sign that one of the front tires has failed. Sometimes, failure of a rear tire will cause the vehicle to slide back and forth or “fishtail.” However, dual rear tires usually prevent this.

Any of the above signs is a warning of possible tire failure, and you should do the following:

• Hold the steering wheel firmly – If a front tire fails, it can twist the steering wheel out of your hand. The only way to prevent this is to keep a firm grip on the steering wheel with both hands at all times.
• Stay off the brake – It is natural to want to brake in an emergency. However, braking when a tire has failed could cause loss of control. Unless you are about to run into something, stay off the brake until the vehicle has slowed down. Then brake very gently, pull off the road and stop.
• Check the tires – After you have come to a stop, get out and check all the tires. Do this even if the vehicle seems to be handling all right. If one of your dual tires goes, the only way you may know it is by getting out and looking at the tires.

By far the most common skid is one in which the rear wheels lose traction through excessive braking or acceleration. Skids caused by acceleration usually happen on ice or snow. They can easily be stopped by taking your foot off the accelerator. (If it is very slippery, push the clutch in. Otherwise, the engine can keep the wheels from rolling freely and regaining traction.)

Drive-Wheel Skids —

Rear-wheel braking skids occur when the rear-drive wheels lock. Because locked wheels have less traction than rolling wheels, the rear wheels usually slide sideways in an attempt to “catch up” with the front wheels. In a bus or straight truck, the vehicle will slide sideways in a “spin out.” With vehicles towing trailers, a drivewheel skid can let the trailer push the towing vehicle sideways, causing a sudden jackknife (see Figure 2-15 on page 45).