6.2 Brake Stroke, Adjustment Limits, and Stroke Indicators

Alberta Air Brake Q Endorsement

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1 Chapter 1: Alberta Q Endorsement Program and Air Brake Fundamentals

1.1 Alberta Q Endorsement Path, Course Requirements, and Knowledge Test Logistics 1.2 Licensing Scope, Farm Vehicle Exceptions, and the Technician Route 1.3 Air Brake System Fundamentals: Compressed Air, Pressure Units, Safety, and Schematic Colours

2 Chapter 2: The Supply Circuit: Compressor, Governor, Tanks, and Air Dryers

2.1 Air Compressors, Drive Systems, and Governor Operation 2.2 Supply and Service Tanks, Contamination, and Draining 2.3 Air Dryers, Air Brake Antifreeze, Safety Valves, and Check Valves

3 Chapter 3: Service Circuits, Control Valves, Gauges, and Low-Air Warnings

3.1 Dual Air Systems: Primary and Secondary Service Circuits 3.2 Brake Chambers, Control Valves, Quick Release Valves, and Relay Valves 3.3 Air Pressure Gauges, Low-Air Warnings, and the Driver's Response

4 Chapter 4: The Park Circuit and Tractor/Trailer Circuits

4.1 Spring Parking Brakes, the Park Control Valve, Compounding, and Caging 4.2 The Tractor Protection System, Trailer Supply Valve, and Glad Hands 4.3 Trailer Service Control, the Trailer Hand Valve, and Air Park Brake Trailers

5 Chapter 5: Air System Failures and Emergency Braking

5.1 Tractor Air System Failures: Supply, Primary, Secondary, and Park Circuits 5.2 Trailer Air System Failures: Service Line, Supply Line, Reversed Lines, and Trailer Tanks

6 Chapter 6: Foundation Brakes and Brake Adjustment

6.1 Foundation Brakes: S-Cam Drum, Disc, and Wedge Brakes 6.2 Brake Stroke, Adjustment Limits, and Stroke Indicators 6.3 Adjusting Manual Slack Adjusters and Maintaining Automatic Slack Adjusters

7 Chapter 7: Braking Fundamentals, Driving Techniques, and Brake Management Systems

7.1 Braking Fundamentals: Heat, Brake Lag, Stopping Distance, and Fade 7.2 Downgrades, Auxiliary Retarders, Bobtailing, and Winter Braking 7.3 Antilock Brakes, Automatic Traction Control, and Stability Control

8 Chapter 8: Vehicle Inspections and the Air Brake Practical Test

8.1 Trip Inspection Law, Major and Minor Defects, and Roadside Enforcement 8.2 Inspection Set-Up and Recognizing Air Brake Defects 8.3 Trip Air Brake Inspection Steps 1–3: Tractor Protection and Park Control Checks 8.4 Trip Air Brake Inspection Steps 4–6: Supply Circuit, Leak Test, Brake Adjustment, and Scoring

6.2 Brake Stroke, Adjustment Limits, and Stroke Indicators

Key Takeaways Explain This Topic AI

Properly adjusted brakes work in the upper half of the pushrod's available stroke; out-of-adjustment brakes work in the lower half, and brake adjustment cannot be felt when driving.

For manual slack adjusters, the optimum free stroke is 1/2 inch (13 mm), and 3/4 inch (19 mm) is the guideline for readjusting; automatic slack adjusters can feel loose and still be within the applied stroke limit.

Applied stroke is measured with a full service application; the maximum limits are 1 3/4 inches (45 mm) for a standard Type 20, 2 inches (51 mm) for a standard Type 30, and 2 1/2 inches (64 mm) for a long-stroke Type 30.

Long-stroke chambers are identified by square inlet (delivery) ports; brakes adjusted too tightly will drag when released.

Brake stroke indicators are required and must be retrofitted if missing; the NSC trip inspection treats any pushrod stroke beyond the adjustment limit as a major defect.

Last updated: September 2026

Brake Stroke, Adjustment Limits, and Stroke Indicators

Quick Answer: A brake chamber delivers its best force in the first part of its stroke, and its force drops to zero as the push plate reaches the end of the chamber. Properly adjusted brakes work in the upper half of the available stroke on the course's force graph. Out-of-adjustment brakes work in the lower half, and you cannot feel the difference when driving . For manual slack adjusters , the optimum free stroke is 1/2 inch (13 mm) , and 3/4 inch (19 mm) means readjust. Measured with a full service application, the maximum applied stroke is 1 3/4 in (45 mm) for a standard Type 20 , 2 in (51 mm) for a standard Type 30 , and 2 1/2 in (64 mm) for a long-stroke Type 30 .

Stroke versus force: why adjustment matters

The student manual uses a graph of brake application force (vertical) against pushrod stroke (horizontal):

At the left, the pushrod is fully retracted and the brake is released.

As the stroke increases, force rises. Properly adjusted brakes use the upper half of the available stroke , the high-force part of the curve.

As the linings wear, the stroke grows. Brakes that are out of adjustment use the lower half of the curve and apply with less force.

As the push plate reaches the end of the chamber, application force drops to zero .

The dangerous part is that drivers may not notice the loss under normal conditions . You can "feel" that the brakes are good and still have them fail when more is asked of them: a heavy stop, a long downgrade, or a load that has heated the drums. Brake adjustment cannot be felt when driving , so it must be checked.

Heat makes an out-of-adjustment brake worse. Hot drums expand away from the linings, so the pushrod must travel even farther for the same application. Brake fade comes partly from this expansion and partly from the reduced friction between hot linings and drums. A brake that was near its limit when cold can run out of stroke when hot.

Free stroke (manual slack adjusters)

Free stroke is how far you can move the slack adjuster by hand (or with a pry bar) before the linings contact the drum, with the brakes released.

Measure Manual slack adjuster guideline
Optimum free stroke 1/2 inch (13 mm)
Readjust when free stroke reaches 3/4 inch (19 mm)

Automatic slack adjusters often feel loose when pulled by hand but are still within the required applied stroke. Do not judge an automatic adjuster only by how loose it feels. Section 6.3 explains how to maintain and confirm automatic adjusters.

Applied stroke: the enforcement method

At a Level 1 CVSA inspection, enforcement officers measure applied stroke :

Chock the wheels and release the spring brakes. Set reservoir pressure to 90–100 PSI and turn the engine off for this CVSA measurement. Mark or measure the pushrod in its released position.

Hold a full service application and measure the change in pushrod position at each brake. Partial applications do not provide the required measurement; excessive reservoir pressure can also give an incorrect result.

Compare each reading with the maximum for the identified chamber type.

Source: CVSA air-brake pushrod stroke measurement procedure .

Chamber Total stroke to bottoming Maximum applied stroke (adjustment limit)
Standard Type 20 2 1/4 in (57 mm) 1 3/4 in (45 mm)
Standard Type 30 2 1/2 in (64 mm) 2 in (51 mm)
Type 30 long-stroke (30LS) 3 in 2 1/2 in (64 mm)

Notice the pattern: for these mid-sized chambers there is about 1/2 inch (13 mm) of reserve between a properly adjusted maximum stroke and the point where the chamber bottoms out. These are maximum adjustment limits . CVSA identifies a stroke violation when travel exceeds the applicable limit; equality alone should not be described as automatically placing the vehicle out of service. A brake close to the limit still needs attention because wear and heat can increase travel. Vehicle-level roadside out-of-service decisions follow their own criteria; the Alberta trip-inspection rule below separately treats travel beyond the limit as a major defect. Brakes should not be too tight either, or they will drag when released.

Identifying long-stroke chambers. Long-stroke chambers are marked "LS" and are recognized by square delivery (inlet) ports . They have a longer limit, so misidentifying one leads to a wrong adjustment judgement. Long-stroke and standard chambers are not interchangeable .

Brake stroke indicators

Many pushrods carry a stroke indicator: knurling painted red , or green, yellow, or red tape , that shows an over-stroke condition when it appears outside the chamber. The Alberta course states that brake stroke indicators are required and must be retrofitted if missing . Canadian Motor Vehicle Safety Standard 121 has required them on air-braked vehicles manufactured on and after May 31, 1996 .

How the adjustment rules are enforced

Daily trip inspection: under the National Safety Code Schedule 1, a pushrod stroke of any brake beyond the adjustment limit is a major defect . The vehicle may not be driven until it is fixed.

Roadside: officers use the applied stroke method above, and out-of-adjustment brakes are a leading reason for out-of-service orders.

Slack adjuster angle

When the brake is applied, the slack adjuster arm and pushrod should be close to a right angle (90 degrees) . This is where the lever turns the most pushrod force into cam torque. As the stroke grows, the arm swings well past 90 degrees, and more of the pushrod's force is wasted. That is one more reason long strokes mean weak brakes.

Automatic slack adjusters at a glance

An automatic slack adjuster that is out of adjustment is a sign of a problem , such as worn parts or a failing adjuster, and the vehicle should go to a repair facility.

The course teaches an emergency adjustment procedure for getting the vehicle safely to a repair facility . It is not routine maintenance, and doing it routinely damages the adjusters (Section 6.3).

Vehicles built with automatic slack adjusters cannot be retrofitted with manual slack adjusters.