FAQs: Brake Systems and Inspections
Self-adjusting brake adjusters (S-ABAs) are required on each brake of all vehicles produced for initial sale in the United States starting Oct.19, 1994, and all vehicles produced for initial sale in Canada starting May 31, 1996. If your vehicle was manufactured after those dates, respective of country, self-adjusting brakes are required.
If your vehicle or combination includes any units that were required to be anti-lock brake system (ABS) equipped at the time of manufacture, those unit(s) must have a functioning ABS malfunction lamp(s) that turns on and then off when power is supplied to the unit. If ABS lamps do not illuminate at all, you likely have a violation. If ABS lamps illuminate and stay on, you also have a violation. Check our field references to see if your vehicle requires a functioning anti-lock brake system (ABS).
View a document on understanding your vehicle’s ABS.
- United States
- Canada
Below are regulation stroke limits for clamp-type brake chambers.
- In safe location, block wheels and release spring brakes.
- Bring air pressure to 90-100 psi and turn off engine.
- Mark pushrods.
- Fully apply and hold brakes.
- Measure and confirm pushrod stroke is within regulation stroke limits.
Size | Marking (available on some chambers) | Outside Diameter(reference) | Regulation Stroke Limit | Manufacturer’s stroke rating (At this stroke length, your brake force drops to zero. Your pushrods should never approach this length.) |
6 | None | 4 ½” (115mm) | 1 ¼” (32mm) | 1 ¾” (45mm) |
9 | None | 5 ¼” (133mm) | 1 3/8” (35mm) | 1 5/8” (41mm) |
12 | None | 5 11/16” (144mm) | 1 3/8” (35mm) | 1 5/8” (41mm) |
16 | None | 6 3/8” (162mm) | 1 3/4” (45mm) | 2 ¼” (57mm) |
16LS | Tag & Marking | 6 3/8” (162mm) | 2” (51mm) | 2 ½” (64mm) |
20 | None | 6 25/32” (172mm) | 1 ¾” (45mm) | 2 ¼” (57mm) |
20LS | Tag & Marking | 6 25/32” (172mm) | 2” (51mm) | 2 ½” (64mm) |
24 | None | 7 7/32” (183mm) | 1 ¾” (45mm) | 2 ¼” (57mm) |
24L | ‘L’ and Stroke Tag | 7 7/32” (183mm) | 2” (51mm) | 2 ½” (64mm) |
24LS | Tag & Marking | 7 7/32” (183mm) | 2 ½” (64mm) | 3 (76mm) |
30 | None | 8 3/32” (205mm) | 2” (51mm) | 2 ½” (64mm) |
30 | ‘DD3’ (Bus/Coach) | 8 1/8” (206mm) | 2 ¼” (57mm) | 2 3/4“ (70mm) |
30LS | Square Ports, Tag & Marking | 8 3/32” (205mm) | 2 ½” (64mm) | 3 (76mm) |
36 | None | 9” (228mm) | 2 ¼” (57mm) | 2 3/4 (70mm) |
Air hoses and tubing must not be worn so as to render them likely to fail. Pages 26-27 of the April 1, 2014, CVSA “North American Standard Out-of-Service Criteria Handbook and Pictorial” state the following:
Brake Hose/Tubing
Roadside enforcement inspectors look for wear and damage to brake hoses and tubing. The following are descriptions of out-of-service (OOS) conditions, along with the U.S. Federal Motor Carrier Safety Regulation number for reference:
- Any damage extending through the outer reinforcement ply. (393.45(a))
NOTE: Rubber impregnated fabric cover is not a reinforcement ply.
NOTE: Thermoplastic nylon tube may have braid reinforcement or color difference between cover and inner tube. Exposure of second color is an out-of-service condition.
- Bulge/swelling when air pressure is applied. (393.45(a))
- Audible air leak at other than a proper connection. (393.45(a))
- Improperly joined such as a splice made by sliding the hose ends over a piece of tubing and clamping the hose to the tube. (393.45(a))
Damaged by heat, broken, or crimped in such a manner as to restrict air flow. (393.45(a))
A performance-based brake tester (PBBT) measures the slow speed brake force and weight at each wheel, adds up the total vehicle brake force, and divides it by the total vehicle weight to determine overall vehicle braking efficiency. U.S. federal regulations and the North American Standard Out-of-Service Criteria require a minimum braking efficiency of 43.5 percent. If your vehicle’s braking efficiency is below 43.5 percent, your brakes are in need of service because they are not providing the minimum stopping power required and are performing poorly.
Click here (PDF) for an example of what an inspection report will show if you are tested on a PBBT. Note that if any wheel end is showing braking efficiency below 43.5 percent, there’s likely something wrong with that brake, even if no violation is found.