April 2013, TruckingInfo.com - WebXclusive
Brake Stroke Indicators
Brake stroke indicators are one of the best ideas to come along since sliced bread, but they aren’t infallible.
The North American Brake Safety Conference recommends the use of effective visual brake stroke indicators as “the single most meaningful change that can be made to improve brake compliance.”
Several types of stroke indicator exist, from colored markings on the push rod itself to external pointers that indicate the length of the pushrod stroke. After a time, the colored markings usually become unreadable because of corrosion or dirt buildup, and they’re difficult to see even at the best of times.
The external types are good, but only as good as their initial setup. If not set up properly, they won’t provide correct information. They can slip over time, too, so periodic verification of the marker placements is necessary.
When visually checking stroke with a brake stroke indicator, drivers have to use the correct procedure, which they often don’t.
1.) With all the brakes released, the system pressure must be built up to between 90 and 100 psi (the same pressure used by officials to check break adjustment). Place the transmission in low gear and shut off the engine. The driver should verify that all the stroke indicators are reading “zero,” or the indicator is in line with the marker closest to the face of the brake chamber, indicating it’s in the rest position. If not, there could be a problem with the return springs or something may be binding elsewhere in the foundation brake, preventing a full retraction of the pushrod.
2.) With the system pressure between 90 and 100 psi, the stroke travel should be checked while making a full brake application. This may require jamming a stick or something between the steering wheel and the brake pedal if you’re working alone. In this state, none of the stroke indicators should read beyond the legal stroke limit.
Checking the brake stroke while the spring brakes are applied isn’t good enough. It’s said that a new parking brake spring with no other mitigating factors will exert the equivalent of about 60 psi of force to the pushrod. That’s still about 40 psi less than is required by an official brake inspection. That additional 40 psi can make a big difference in stroke travel, especially where loose or worn componentry is present. That difference could be enough to force the pushrod beyond its stroke limit.
If you’re an owner-operator, stroke indicators are a no-brainer. Set up properly, maintained, and used according to the instructions, brake stroke indicators are a near sure-fire way to keep your auto slacks from running away from you.