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VAPOUR LOCK IN CAR BRAKING SYSTEMS

Laboratory studies determined that a water content of 1% in current brake fluids reduces the vapor lock point from 250 degrees C to 180 degrees C, with further increases in water content having progressively less effect. Comparative tests on nine car models were carried out on the track to measure brake fluid temperatures, and fluid temperatures were measured for one car under a variety of road conditions. Under normal conditions, maximum fluid temperatures were 50 to 60 degrees C. With a fully laden car or one with worn brake pads, fluid temperatures were increased. A simulated binding rear brake raised the fluid temperature to 143 degrees C in the rear brake cylinder. During an extremely severe hill descent of a fully loaded car, the fluid temperatures were 150 to 160 degrees C. Over half the cars in a national sample of 1000 had 3% or more water in their brake fluids, corresponding to a vapor lock point of 145 degrees C. A firm relationship between fluid age and water content could not be established. Indications are that fluid changes at intervals of less than three years would result in only small improvements. Vapor lock should not be a problem for current cars under normal operating conditions in the U.K. unless the fluid is severely contaminated with moisture and either the car is at the end of a severe descent or some of its brakes are binding.

  • Corporate Authors:

    Transport and Road Research Laboratory

    Vehicle Safety Division, Old Wokingham Road
    Crowthorne RG11 6AU, Berkshire,   England 
  • Authors:
    • Keen, J
  • Publication Date: 1979

Media Info

  • Features: References;
  • Pagination: 33 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00384731
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: LR 903, HS-029 091
  • Files: HSL, ATRI, USDOT
  • Created Date: May 30 1984 12:00AM