The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day as part of his/her pre-trip inspection.
In some jurisdications, drivers must use the applied stroke method; in others, they are allowed to use the pry bar method.
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Know which method you are to use to determine if the brakes are in adjustment for your province or territory. TOOLS REQUIRED: gloves, safety glasses, wheel chocks, measuring device, device to mark push rod at fix point.
1) Block wheels, build system pressure is at maximum pressure, and release spring brakes.
i) Air dryer purges;
ii) Confirm that needles have stopped climbing between 105 psi & 135 psi.
2) Mark all push roda at a fix point.
3) Using another person or a bit of wood, apply the brake pedal on full and hold.
i) if the trailer service brakes wrap the seat belt around the trailer hand valve.
4) At the brake chamber, measure from the fixed point to the mark on the push rod.
5) Type 30 Brake Chamber equipped with manual slack adjusters has a maximum allowable push rod travel of 1 3/4 inches (44 mm).
6) Type 30 Brake Chamber equipped with automatic slack adjuster has a maximum allowable push rod travel of 2" inches (5 cm).
5) If the push rod stroke is more that 1 3/4" inch (44 mm), the manual slack adjuster has to be adjusted.
6) If the vehicle is equipped with an automatic slack adjuster, it may have to be assessed & repaired by a qualified mechanic.