Air Brake Manual

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Service tests

  • Apply the brakes and check that the slack adjusters rotate freely without binding.
  • Release the brakes and check that the slack adjusters return to their released position without binding.
  • With brakes released, check that the angle formed by the slack adjuster arm and push rod is greater than 90 degrees (Fig. 52). All slack adjusters should be adjusted to this same angle.
    Note: The practical test will include proper adjustment of a manual slack adjuster and a verbal explanation of the proper procedure for adjusting an automatic slack adjuster.
  • With brakes applied (20 psi [138 kPa]), check that the new angle is no less than 90 degrees and that all slack adjusters have the same amount of travel.
Trailer spring-brake valve
Figure 52. Slack adjuster and push rod angle
Automatic slack adjuster
Figure 53. Automatic slack adjuster


Rev: 2018