Checking brake stroke is a time-honored tradition, and it often reveals problems – but how much does it really tell you? The answer, of course, is that it tells only part of the story, providing what Doug Woolverton – director of the safety equipment division of Hunter Engineering – calls “essentially a prediction of performance.”
A far more useful measurement would be the actual brake force produced by the chamber and other brake actuation hardware, linings and drum. Thus, “PBBTs,”or performance-based brake testers – the terminology echoing that referring to the use of actual crash statistics in determining truck inspection standards – have become available. These systems measure actual stopping force at the tread contact patch when the brakes are applied, using either an electrically driven roller or pads equipped with load cells.
David Domine, Link-Radlinski’s general manager, says PBBTs can find a few things a stroke check cannot: weak or ineffective service brakes due to glazed or contaminated linings, or rusted/inoperative components; weak or broken spring brakes; brake or threshold pressure imbalance; drum ovality or eccentricity; valve problems; and bearing failures. The Link-Radlinski system rolls the wheel to measure drag, which allows it to test ABS system performance, confirming proper sensor and valve operation and revealing reverse operation, as well as finding bearing drag, Domine says.
The same goes for the VIS-Check system. “Vehicles that have a regular VIS-Check inspection run straighter, rise smoother and brake better than those managed using conventional PMI activities,” the company says. Like the Link-Radlinski system, “VIS-Check measures the rolling resistance at each wheel end and flags issues by wheel position as part of each brake test.”
Other types of problems that a tester can reveal include contaminated friction material, mismatched friction materials, and grabbing due to unseen mechanical problems in S-cams and bushings, Woolverton says.
Domine says other practical advantages of a PBBT are that it is noninvasive, does not require the inspector to get under the vehicle, and can perform its work much more quickly than a standard inspection. However, a PBBT cannot identify potential future failures such as leaks, chaffed air lines, worn linings or other visual defects, he says.
A critical challenge for a fleet maintenance manager or other senior executive is cost justification for a system that may run from nearly $30,000 for a system that sits on an existing floor, to nearly $100,000 when requiring concrete work.
“In states where inspection is required, use of the brake tester saves time and testing costs,” says Bruce Jensen, general manager of Castle Equipment Co., which sells the Weaver Brake Tester. “The brake tester gives an instantaneous reading, allowing quick diagnosis of brake problems. Marginal problems can be corrected before they turn into major failures.”
Woolverton agrees, saying that cost justification can be performed by tracking and comparing controllable expenses such as insurance, solving chronic problems that lead to lining wear, and failed roadside inspections leading to out-of service vehicles and downtime.
Domine says that by using a brake tester, fleets can realize improved brake life; improved life of related components, especially tires; improved maintenance efficiencies (reduced diagnostic time and driver complaints); improved fuel economy because of reduced brake drag; reduced litigation costs (reduced dollars per claim); reduced accident risk exposure; and potential reduction in insurance costs.
“Some insurance companies offer favorable consideration to fleets operating a PBBT,” VIS-Check says.
Also keep in mind that these systems immediately reveal brake force imbalance, which allows restoration of a situation where all the wheels provide their fair share of brake force. This will improve vehicle stability (especially where ABS is not present on the trailer), reduce ABS actuation cycles and thus wear to related components, and extend the time until the next brake job is required because of lower operating temperatures on the hottest wheels. Where trucks operate on mountain roads, this could help prevent a runaway.
Just how many vehicles a fleet needs to justify the cost is a complex question. Jensen pegs the number at as few as 25. Woolverton says fleets should make their own calculation. “A fleet’s direct return on investment would depend on improvements to the overall fleet efficiency and the desire to capitalize on reduced downtime, less accident risk, and better overall maintenance practices that spot problems before serious consequences with serious costs occur,” he says.
Domine says cost justification depends on the vocation. “A waste-hauling fleet of 50 or 60 heavy trucks may be able to see a return on investment in less than two years, while an over-the-road fleet may need 300 trucks to see a return in that time,” he says.
Fortunately, smaller fleets can take advantage of this technology via outsourcing. Jensen says most Weaver testers are found in states running an inspection program, including Illinois, New Jersey, Louisiana, Texas and Washington, D.C. Many of Hunter’s testers also are in state testing programs. Link-Radlinski has dealers in the Southeast, East and Central regions, and has its own activity in the Midwest and South; some of these dealers will come to a fleet’s facility and provide equipment and manpower to test every truck, Domine says.
With suppliers and equipment like these, perhaps it’s time to explore the advantages of using a PBBT to shed a lot more light on your braking problems in a lot less time.