How to adjust a manual slack adjuster for your cdl air brakes?

Manual Slack Adjuster Adjustment for CDL Air Brakes

(Operation Specifications for Manual Slack Adjusters for Commercial Vehicle Air Brakes)
1. Pre-Operation Preparations
Removing the Air Tank:
With the ignition off, continuously depress the brake pedal until the pressure gauge returns to zero and a hissing sound is heard from the exhaust valve for at least 3 seconds.
Wedge Double Safety:
Place wedges in both directions, behind the front wheels and in front of the rear wheels. Never park the vehicle solely by engaging a gear.
Removing the Guard:
Use a flat chisel to remove the dust cover from the adjustment hole (the cast iron cover must be heated before removal to prevent chipping).

2. Clearance Inspection and Adjustment
Feeler Gauge Method:
Insert a feeler gauge into the clearance between the brake push rod and the adjusting arm (usually 0.9-1.2mm). Adjust if too loose or too tight.
Do not use the "turn the wheel to measure resistance" method—it can cause significant inaccuracies when the drum is deformed.
Hex Wrench Operation:
Turn the adjustment worm counterclockwise (on most models) until the feeler gauge cannot be inserted (the shoe is firmly against the brake drum). Back out the exact number of teeth:
US models: Back out 3 worm teeth (approximately 120°)
European models: Back out 1/4 turn (90°)
Lock to prevent loosening:
Holding the wrench in place, tighten the lock nut to 150-200 N·m using a 36mm ring wrench (a torque wrench is required). 

3. Ironclad Rules for Avoiding Potholes
Overtightening: Death Sentence:
Overtorque the locknut → Deformed threads → Unable to adjust next time
Insufficient retraction → Brake drum 400°C+ while driving → Tire spontaneous combustion
Loseness: Fatal Chain Linkage:
Under-required torque → Vibration loosening → Uncontrolled clearance → Pushrod ruptures the diaphragm → Air pressure returns to zero, braking stops

4. Post-mortem Verification after Adjustment
Test Items
Qualification Criteria
Critical Risk
Static Clearance: A feeler gauge with resistance when inserted into a 1.0mm thick gauge is moved. Overtightening: Drag and burnout; Overloosening: Braking lag
Pushrod Travel: Pushrod travel 25-38mm when braking (visual inspection + ruler measurement). Exceeding 40mm = Precursor to diaphragm rupture
Brake Drum Temperature Difference: Infrared temperature measurement after 3km of driving: Left and right drum temperature difference ≤15°C. A temperature difference of 30°C indicates adjustment imbalance → biased braking.
Manual Rotation Resistance: Lift the wheel and rotate the tire with one hand (wear gloves to prevent burns). Requires force = overtightening; completely free = overloose.

5. Special Operating Conditions
Extremely Cold Winter Operation:
Before adjustment, use a propane torch to heat the locknut for 10 seconds (below -20°C) to prevent brittle fracture.
Preheat the feeler gauge to body temperature to prevent it from sticking when inserted cold.
Worn Steps on the Brake Drum:
Use an angle grinder to smooth the steps on the inner wall of the drum before adjustment. Otherwise, the measured clearance will be distorted.