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 manufacturer's maintenance and repair manual of the vehicle that you are working on.
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:
1. Repressurize the system before attempting to make repairs.
2. Do not work on an antilock brake system with the ignition turned on. (Damage to the system computer can result.)
3. Do not substitute parts. Use parts that are approved for the system you are working on.
4. Keep the correct size tires on your vehicle. Mismatched tire sizes will give the computer false readings.
5. Check the speed sensors for cleanliness. A dirty speed sensor will give the computer a false, or zero reading.
6. 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 system computer.
7. An incorrect air gap on the wheel sensors will lead to false input to the antilock brake system computer.
8. DO NOT USE SILICONE BRAKE FLUID in a vehicle equipped with an antilock brake system.
9. If electric arc welding must be done to the vehicle you are working on, disconnect the antilock brake system computer first.
10. A low battery caused by a faulty charging system will cause the antilock brake system to malfunction.
11. Antennas for transmitting type radios should not be located near the computer of antilock brake system.
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 manufacturer's service and repair manual of the vehicle you are working on.Continue Reading