Drivers depend heavily on their brakes but may not always be aware of shortcomings or defects if they never “exercise” their brakes. Regular inspections are critical, but they have to be more than just a glance in the direction of the wheels.
Photo: Jim Park
Drivers are required to know a few basics about their brake systems in order to pass the CDL test, but how much of what they learned in school do they retain and practice every day? Can they recognize a problem before it becomes mission crippling? Can they properly perform basic brake system inspections? Back in 2012, the Commercial Vehicle Safety Alliance published a brake quiz aimed at drivers and technicians. A total of 895 drivers and 404 technicians participated in the survey. The results that came back were troubling.
That was eight years ago, and to the best of my knowledge CVSA has not published a quiz since. But looking back on the past decade of brake inspection violations recorded in various announced and unannounced inspection blitzes, the number of violations as stayed about the same, give or take a few percentage points.
CVSA Roadcheck Brake System and Brake Adjustment OOS (2012-2021)
I've never felt that drivers alone should be responsible for the condition and function of the brake system (technicians and fleet maintenance policies should be held to account in some cases), but I would agree that drivers should know how to inspect their brake systems effectively enough to detect potential trouble and then report the problems to management. If management elects not to deal with the problem, then the violation should be on the fleet too.
But if drivers don't know how to inspect their brakes, how are they to detect a problem?
On the section of the drivers' quiz that asked "right or wrong" questions about basic brake stuff that would help drivers in an inspection, the average score was 57%. In its analysis of the results, Battelle Memorial Institute that years of experience did not correlate directly with higher scores. The analysis did reveal the largest percentage of those scoring ≥ 60% had 20+ years of experience while the majority of those scoring ≤ 30% had 4 or fewer years of service.
It may be a stretch to make this assumption, especially with a survey that's nearly 10 years old, but with the average number of years on the job dropping today with the departure of many senior experienced drivers, it might behoove industry to go back to newer less experienced drivers to see what they actually know about inspecting brakes.
An up-and-coming technician demonstrates a disc brake pad change during Rush Truck Centers Tech Skills Rodeo, designed to foster skills development.
Photo: Jim Park
So, here are a few of the questions CVSA asked in that original survey. These relate to basic brake function and details drivers should know about their brakes.
The correct answers appear at the end of the story.
Drivers’ Questions
1. Brakes with automatic slack adjusters…
_ Seldom go out of adjustment.
_ Need adjustment on a regular basis.
_ Should be checked periodically to make sure pushrod stroke is within proper limits.
2. Indicate the conditions for properly checking brake pushrod stroke.
A) Air pressure in the reservoir must be:
_ 60 psi
_ does not matter
_ 90 to 100 psi
_ 100 to 120 psi
B) Service brakes must be:
_ Released
_ Partially applied
_ Fully applied
C) Spring brakes must be:
_ Applied
_ Released
D) Engine must be:
_ Running
_ Shut off
_ It doesn’t matter
3. Indicate whether the following statements are true or false.
A) When service brakes are out-of-adjustment, spring brakes are still able to provide full brake force capability.
B) The angle between the pushrod and slack adjuster can be used to determine brake adjustment.
C) The brake stroke limit is the same for all types of brake chambers.
D) Using automatic slack adjusters makes inspecting brake stroke unnecessary.
4. Which is the correct methods to determine when brakes need to be adjusted?
_ "Feel” of the brakes
_ Slack adjuster angle
_ Measuring pushrod stroke
_ Mileage
Slack adjusters at a 90-degree angle to the push rod is a good visual reference that the brakes are probably adjusted properly, but it’s no guarantee. Brake stroke indicators help too, but if brakes are visually inspected with the spring brakes applied, that’s equal to a bit more than half of the 90-100 psi application pressure needed to perform a proper stroke measurement.
Photo: Jim Park
Technicians' Questions
The service technician survey consisted of 25 questions requiring a total of 31 responses. Four of the questions were designed to describe the characteristics of the technician. The remaining 21 questions required 27 right or wrong responses and were designed to measure technicians’ knowledge of brakes and brake inspection and adjustment methods.
Overall, 59% of the participating technicians scored 60% or higher while 11% scored 30% or lower. Only 18% scored 80% or higher. The average score for technicians who left some of the responses blank was just 53%. For technicians who answered all the questions, the average score was 68%.
Here's a sample of 15 questions directed to technicians from that 2012 quiz. How well to you think your techs would score?
1. Indicate the conditions for properly checking brake pushrod stroke.
A) Air pressure in the reservoir must be:
_ 60 psi
_ 90 to 100 psi
_ 100 to 120 psi
_ Does not matter
B) Service brakes must be:
_ Released
_ Partially applied
_ Fully applied
C) Spring brakes must be:
_ Applied
_ Released
D) Engine must be:
_ Running
_ Shut off
_ Does not matter
2. Are tractors and/or trailers, manufactured after October 20, 1994, permitted to be equipped with Manual Slack Adjusters?
_ Yes
_ No
_ There is no age requirement
3. When performing the Federal Periodic Inspection, how many brakes are allowed to be 1/4 inch or more beyond the readjustment limit, before failing the equipment?
_ 0
_ 1
_ 2
_ 20%
4. What is the longest push rod stroke allowed for a Type 20 or 24 standard stroke brake chamber?
_ 2 ¾
_ 1 ½
_ 2
_ 1 ¾
_ No requirement
5. What is the longest push rod stroke allowed for Type 30 standard stroke brake chamber?
_ 1 ½
_ 2
_ 2 ½
6. Do worn cam shaft bushings have an effect on brake stroke?
7. Indicate whether the following statements are true or false:
A) Brake lining on a non-steering axle with air drum brakes must be at least ¼ thick.
B) Brake chambers on each end of a steering axle can be a different size.
C) Drivers can normally tell when the brakes on their tractor or trailer are out of adjustment by the feel of the brakes.
D) Automatic slack adjusters need to be adjusted manually every so often.
E) Checking the Low Air Warning device in the tractor is part of the Periodic inspection process.
8. What do you do when you find a brake having an Automatic Slack Adjuster with excessive pushrod stroke?
_ Adjust them
_ Replace the automatic slack adjuster
_ Further inspect Foundation Brakes for possible issues following a diagnostic procedure, such as TMC’s RP 609B.
_ Contact the manufacturer for trouble shooting procedures.
9. How do you perform a free stroke test?
_ Use a pry bar to determine adjuster movement until brake shoes contact drum
_ Apply the parking brakes
_ Apply brakes at 90-100PSI
10. Dragging brakes are caused by which of the following?
_ Mis-installation of the automatic slack adjuster
_ Mis-piloted brake drum
_ Worn cams/bushings and return springs
_ Partial parking brake application.
_ All of the above
11. Brake stroke that is not within the DOT requirements can be caused by which of the following?
_ Manual slack adjuster not adjusted
_ Automatic slack adjuster not working
_ Foundation brake problems
_ All listed
12. Free stroke greater than the manufacturers limit indicates a problem in what part of the brake system? (check all that apply)
_ The Automatic slack adjuster
_ The Foundation brake problem
_ The Pressure in the air reservoirs
13. A brake measured to be out-of-stroke when activated using 90-100 psi air pressure, but with a Free Stroke within the manufacturers limit, indicates a problem in what part of the brake system?
_ The Automatic slack adjuster
_ Foundation Brake Problem
14. What is the Legal stroke limit for a 3” maximum stroke long stroke chamber?
_ 0”
_ 1-3/4”
_ 2”
_ 2-1/2”
15. When replacing the brake linings, drums or servicing the hub assembly there is no need to inspect the ABS wheel speed sensor.
_ True
_ False
Technicians need to be aware of the technical standards that apply to brakes as well as a weather eye for problems that drivers may not be aware of.
1. Brakes with automatic slack adjusters…: Should be checked periodically to make sure pushrod stroke is within proper limits.
2. Indicate the conditions for properly checking brake pushrod stroke.
A) Air pressure in the reservoir must be: 90 to 100 psi
B) Service brakes must be: Fully applied
C) Spring brakes must be: Released
D) Engine must be: Shut off
3. Indicate whether the following statements are true or false:
A) When service brakes are out-of-adjustment, spring brakes are still able to provide full brake force capability. False
B) The angle between the pushrod and slack adjuster can be used to determine brake adjustment. False
C) The brake stroke limit is the same for all types of brake chambers. False
D) Using automatic slack adjusters makes inspecting brake stroke unnecessary.False
4. Which is the correct methods to determine when brakes need to be adjusted?: Measuring pushrod stroke
Technicians' Brake Quiz Answers
1. Indicate the conditions for properly checking brake pushrod stroke.
A) Air pressure in the reservoir must be: 90 to 100 psi
B) Service brakes must be: Fully applied
C) Spring brakes must be: Released
D) Engine must be: Shut off
2. Are tractors and/or trailers manufactured after October 20, 1994 permitted to be equipped with Manual Slack Adjusters? No
3. When performing the Federal Periodic Inspection, how many brakes are allowed to be 1/4 inch or more beyond the readjustment limit, before failing the equipment? 0
4. What is the longest push rod stroke allowed for a Type 20 or 24 standard stroke brake chamber? 1 ¾
5. What is the longest push rod stroke allowed for Type 30 standard stroke brake chamber? 2
6. Do worn cam shaft bushings have an effect on brake stroke? Yes
7. Indicate whether the following statements are true or false:
A) Brake lining on a non-steering axle with an air drum brake must be at least ¼ thick. True
B) Brake chambers on each end of a steering axle can be a different size. False
C) Drivers can normally tell when the brakes on their tractor or trailer are out of adjustment by the feel of the brakes. False
D) Automatic slack adjusters need to be adjusted manually every so often. False
E) Checking the Low Air Warning device in the tractor is part of the Periodic inspection process. True
8. What do you do when you find a brake having an Automatic Slack Adjuster with excessive pushrod stroke?: Further inspect Foundation Brakes for possible issues following a diagnostic procedure, such as TMC’s RP 609B.
9. How do you perform a free stroke test?: Use a pry bar to determine adjuster movement until brake shoes contact drum.
10. Dragging brakes are caused by which of the following?: All of the causes listed.
11. Brake stroke that is not within the DOT requirements can be caused by which of the following? All of the causes listed.
12. Free stroke greater than the manufacturers limit indicates a problem in what part of the brake system? (check all that apply): The Automatic slack adjuster; The Foundation brake problem
13. A brake measured to be out-of-stroke when activated using 90-100 psi air pressure, but with a Free Stroke within the manufacturers limit, indicates a problem in what part of the brake system?: Foundation Brake Problem
14. What is the Legal stroke limit for a 3” maximum stroke long stroke chamber? 2-1/2”
15. When replacing the brake linings, drums or servicing the hub assembly there is no need to inspect the ABS wheel speed sensor. False
A truck driver and owner-operator for 20 years before becoming a trucking journalist, Jim Park maintains his commercial driver’s license and brings a real-world perspective to Test Drives, as well as to features about equipment spec’ing and trends, maintenance and drivers. His On the Spot videos bring a new dimension to his trucking reporting. And he's the primary host of the HDT Talks Trucking videocast/podcast.
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