Page 203 - Driving Commercial Vehicles Manual+

chapter 9 — air brake adjustment

2. Pull the pushrod out from the brake chamber, using a tool like a pry bar
driving tip for leverage.

3. Measure the distance between the chalk mark and the face of the brake
Make sure you have the
proper equipment to check chamber.
the brakes. You’ll need: The distance between the mark on the pushrod and the face of the brake
• a flashlight to inspect chamber is called the free stroke (½ to ¾ of an inch — 12 to 20 mm is a good
components range). If this distance is more than ¾ of an inch (20 mm), the brakes need
• chalk or other marker, and adjustment.
a ruler or other marking
device, to check pushrod
free stroke Brake adjustment indicators
• a tool to pry on the air New air brake chamber pushrods have a marking (usually red) to indicate
brake chamber pushrod when brake adjustment must be done immediately. If the pushrod travel
to check for free stroke
• a wrench to adjust manual becomes excessive, the marking will show.
slack adjusters. Don’t wait until the red marking is exposed before adjusting the brakes.
You should also wear sturdy
clothing, a hard hat and eye
protection.

If the red marking on the
pushrod (at the chamber
face) is visible, it indicates
that the brake is dangerously
out of adjustment and it
needs immediate attention.

Brake adjustment — manual slack adjuster
driving tip
With a typical Type 30 clamp type air chamber, you must adjust the brakes if
While checking air brakes pushrod travel is:
look for other brake
component wear and • more than ¾ of an inch (20 mm) using the pry method of free stroke
excessive play including: measurement, or
• s-cam bushing wear • more than 1¾ of an inch (45 mm) using the brake application — applied
• s-cam spline wear stroke measurement method.
• slack adjuster play (worn Note that these are maximum measurements. You should adjust the brakes if
gear) your measurements approach these limits.
• clevis pin wear.

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