It is important to note that the body design and suspension of some vehicles may limit safe access to certain brake components unless the vehicle is supported on a hoist or is over a pit or ramp. Also, some brake systems have covers or housings that conceal the brake linkage, making it impossible to inspect brake adjustment using the techniques described here.
- Secure the vehicle with wheel chocks or blocks.
- Ensure air pressure is above 621 kPa (90 psi) and release the spring brakes.
- Select one of the following methods:
- Method 1: Mark the pushrod at the brake chamber or at a suitable fixed reference point. (Use chalk, soapstone, marker or other similar instrument — marks must be narrow and precise.)
- Method 2: Measure the released position of the pushrod. (Measure and note the distance from a point on the pushrod to a suitable fixed point at the brake chamber. This is measurement number 1.)
- Raise or lower the air pressure by running the engine or pumping the brake pedal until both the primary and secondary air tank gauges display 621 to 690 kPa (90 to 100 psi).
- Shut off the engine.
- Press and hold the brake pedal in the fully applied position.
- Determine the applied pushrod stroke. (Continue to use the previously selected method).
- Method 1: Measure the distance from the brake chamber or fixed reference point to the mark on the pushrod.
- Method 2: Measure the applied position of the pushrod. (Remeasure and note the distance from the previously selected point on the pushrod to the previously selected fixed point at the brake chamber. This is measurement number 2.) Subtract measurement 1 from measurement 2 to calculate the applied pushrod stroke measurement.
- Determine the number size (such as 16, 20, 24 or 30) and type (such as standard or long-stroke) of the brake chamber.
- Determine the adjustment limit for the brake chamber. (See the chart on page 85.)
- Compare the applied pushrod stroke to the applicable adjustment limit and identify any brake that exceeds the adjustment limit as defective.
Note: All drivers are required to demonstrate an applied pushrod stroke measurement method for inspecting brake adjustment as part of the Ministry of Transportation air brake endorsement practical examination.