Commercial Driver Handbook ( PDF ) - California Department of ...

If the lamp stays on after the bulb check, or goes
on once you are under way, you may have lost
ABS control on one or more wheels.
Remember, if your ABS malfunctions, you still
have regular brakes. Drive normally, but get the
system serviced soon.
Safety Reminders
ABS won’t:
• Allow you to drive faster, follow more closely,
or drive less carefully.
• Prevent power or turning skids. ABS should
prevent brake-induced skids or jackknifes, but
not those caused by spinning the drive wheels
or going too fast in a turn.
• Shorten your stopping distance. ABS will help
maintain your vehicle control, but will not
always shorten your stopping distance.
• Increase or decrease the vehicles ultimate
stopping power. ABS is an “add-on” to your
normal brakes, not a replacement for them.
• Change the way you normally brake. Under
normal braking conditions, your vehicle will
stop as it always has. ABS only comes into play
when a wheel would normally have locked up
because of over braking.
• Compensate for bad brakes or poor brake
maintenance.
Remember:
• The best vehicle safety feature is still a safe
driver.
• Drive carefully, so you never need to use your
ABS.
• If you need it, ABS could help to prevent a
serious crash.
SkID cOntROl/RecOVeRy
A skid happens whenever the tires lose their grip
on the road. This can be caused by:
• Overbraking. Braking too hard and locking
up the wheels. Skids also can occur if you use
the speed retarder when the road is slippery.
• Oversteering. Turning the wheels more
sharply than the vehicle can turn.
• Overacceleration. Supplying too much power
to the drive wheels, causing them to spin.
• Driving too fast. Most serious skids result from
driving too fast for road conditions.
Drivers who adjust their driving to road conditions
do not overaccelerate and do not have to overbrake
or oversteer.
rear or drive Wheel skids
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 be easily
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.)
Rear wheel braking skids occur when the rear drive
wheels lock. Locked wheels have less traction
than rolling wheels, so 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 drive wheel skid
can let the trailer push the
towing vehicle sideways,
causing a sudden jackknife.
(Figure 2-10)
drive Wheel skids
Direction
of Slide
Rear Tractor
Wheels Lock-
Up or Spinning
Line of
Travel
Figure 2-10
Stop braking. This will let the rear wheels roll
again and keep them from sliding any further. If on
ice, push in the clutch to let the wheels turn freely.
Turn quickly. When a vehicle begins to slide
sideways, quickly turn the wheel in the direction
you want the vehicle to go.
Countersteer. As a vehicle turns back on course,
it has a tendency to keep right on turning. Unless
you turn the steering wheel quickly the other way,
you may find yourself skidding in the opposite
direction.
Learning to stay off the brake, turning the steering
wheel quickly, pushing in the clutch, and
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