The SAE recommended practice J1802, Brake Block Effectiveness Rating [1], has the purpose of establishing a uniform procedure for determination and classification of brake effectiveness for commercial vehicle brakes. The practice provides a means to characterize the friction properties of truck brake lining materials in a representative S-cam brake. However, the test has been found to exhibit an unacceptably large range of variability in the implied friction coefficient for the lining. It has been postulated that some of the variability arises from factors within the brakes that are used for the test. A computer model of an S-cam brake was developed to help examine various brake parameter sensitivities. The model calculates brake torque for a specified set of geometry, friction properties, and constant input air chamber force. It assumes that the brake is in a state of equilibrium defined by equalized wear rates on the leading and trailing shoe linings. The parameter sensitivity findings indicate that a potentially significant source of torque variability is related to possible offsets between the drum turning axis and the spider/shoe assembly centerline. Other significant factors include bearing and roller pin friction and the shape of the cam profile. Offsets in the cam shaft center and asymmetric shoe lining stiffnesses contribute to significant differential wear between the leading and trailing shoes. The issue of torque effectiveness variability and its relationship to the SAE J1802 Recommended practice is also discussed.

  • Corporate Authors:

    University of Michigan Transportation Research Institute

    2901 Baxter Road
    Ann Arbor, MI  United States  48109-2150

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • MacAdam, C C
    • Gillespie, T D
  • Publication Date: 1998-12-20


  • English

Media Info

  • Pagination: 120 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00796205
  • Record Type: Publication
  • Report/Paper Numbers: UMTRI-98-55,, Final Report,, HS-808 974
  • Contract Numbers: DTFH61-96-C-00038
  • Files: HSL, TRIS, USDOT
  • Created Date: Jul 14 2000 12:00AM