Federal Motor Carrier Safety Regulations Pocketbook,
par. 393-52, lists emergency brake requirements.
The first antilock brake systems (ABSs) were
developed and used in aircraft in the early 1950s.
Certain automobiles had the systems in the experimental
stages in the mid 1950s and in the production stages in
the early 1970s. The ABSs are common today in many
production cars and trucks.
Why wc use ABS is simple, CONTROL. A high
percentage of vehicle accidents on the highway are
caused by skidding. Since braking is most effective and
steering is not lost when the wheels are still rotating, the
antilock brake system prevents skidding by allowing the
wheels to continue turning during maximum braking
effort. On wet pavement, hydroplaning of the tires is
cut to a minimum. One final benefit is that of extended
tire wear by the elimination of flat spots caused by brake
lockup during panic stops.
All ABS (either two wheel or four wheel) operate
on the same principle. That is, the system is monitored
by an electronic control module for the rate of reduction
of vehicle wheel speed during brake system operation.
If the system feels that lockup is about to occur at one
or more wheels, modulated hydraulic pressure is fed to
that brake caliper by a hydraulic control unit or an
electro-hydraulic valve. In this way, even if hydraulic
pressure is not the same at each wheel, maximum tire
adhesion to the road surface is maintained. Once again,
the way the modulated hydraulic pressure is maintained
is different with each manufacturer. Before going any
further, get a copy of the manufacturers maintenance
and repair manual of the vehicle that you are working
While these systems are not yet common in the
Naval Construction Force, the first equipment you arc
most likely to see the system used on is automotive type
CESE. Very little should malfunction on the system. If
the ABS is in need of repair, you should take the
following precautions before working on it:
Repressurize the system before attempting to
Do not work on an antilock brake system with
the ignition turned on. (Damage to the system
computer can result.)
Do not substitute parts. Use parts that are
approved for the system you are working on.
Keep the correct size tires on your vehicle.
Mismatched tire sizes will give the computer
Check the speed sensors for cleanliness. A
dirty speed sensor will give the computer a
false, or zero reading.
Wheel lugs must be torqued to the correct foot
pounds and in proper sequence. Your failure to
do so may distort the wheel and sensor, thus
sending incorrect readings to the antilockbrake
An incorrect air gap on the wheel sensors will
lead to false input to the antilock brake system
DO NOT USE SILICONE BRAKE FLUID in
a vehicle equipped with an antilock brake
If electric arc welding must be done to the
vehicle you are working on, disconnect the
antilock brake system computer first.
A low battery caused by a faulty charging
system will cause the antilock brake system to
Antennas for transmitting type radios should
not be located near the computer of antilock
Using an improper test method on these
systems can lead to damage to the system or
personal injury to yourself or to the personnel
working for you.
All antilock brake systems have special
system bleeding instructions. Your failure to
follow these instructions will lead to an
inoperative or a faulty system.
For further reading concerning antilock braking
systems, consult your manufacturers service and repair
manual of the vehicle you are working on.