Federal  Motor  Carrier  Safety  Regulations  Pocketbook, par. 393-52, lists emergency brake requirements. ANTILOCK BRAKES 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. 2. Repressurize  the  system  before  attempting  to make repairs. Do not work on an antilock brake system with the ignition turned on. (Damage to the system computer can result.) 3. 4. 5. 6. 7. 8. 9. 10. 11. 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 false  readings. 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 system  computer. An incorrect air gap on the wheel sensors will lead to false input to the antilock brake system computer. DO NOT USE SILICONE BRAKE FLUID in a  vehicle  equipped  with  an  antilock  brake system. 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 malfunction. Antennas  for  transmitting  type  radios  should not be located near the computer of antilock brake  system. CAUTION 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. CAUTION 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. 6-19