Operational Check/Troubleshooting
Operational Check
1.Measure the pushrod length (distance from the face of air chamber to the centerline of the pushrod clevis pin) when
fully retracted, step 1. (See Figure 20.)
2.Have an assistant make an 80 to 90 psi brake application. Measure pushrod length again, step 2.
3.Subtract the step 1 dimension from step 2. The difference is the “applied stroke.”
4.Verify that the applied stroke is less than the maximum specified below.
Air Chamber Type | Maximum Applied Stroke | |
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Type 36" |
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Type 30" | 2" |
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Type 24" |
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Type 24" | 2" |
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(with |
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stroke) |
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Type 20" and 16" |
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Type 12" |
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Verify the correct installation of the control arm. If the self adjusting brake adjuster does not maintain proper applied stroke, it must be replaced.
Troubleshooting
Tight or Dragging Brakes
Check foundation brake components for:
•Control arm anchor bracket not positioned properly (See brake adjuster installation procedures.)
•Brake chamber not fully releasing
–Spring brake not fully releasing
–Pushrod binding on chamber housing
–Air supply not exhausting completely
•
•Extreme differences in
•Improper wheel bearing adjustment
•Broken shoe return spring
•Loose brake linings
Excessive Chamber Pushrod Travel
Check foundation brake components for:
•Loose, broken or bent control arm anchor bracket
•Worn camshaft bushings
•Loose air chamber mounting
•Binding camshaft
•Worn clutch assembly (See Checking Release Torque.)
CONTROL
ARM 
AIR
CHAMBER
SELFAUTOMAADJUSTICING
BRAKESLACKADJUSTER
STEP 2
APPLIED
5 4
3 2 1 0
STEP 1
RETRACTED
Figure 20 Measuring Pushrod Length
13