TMC Developing S-cam Brake Troubleshooting Guide

Work is underway on a long-overdue Recommended Practices document addressing excessive applied stroke in S-cam brakes. The RP will provide a diagnostic and troubleshooting guide to help technicians repair the actual cause of an brake taken out-of-service because of excessive push-rod travel.

Photo: Jim Park

Discussions took place during Monday's S.6 Chassis & Brake Task Force meeting, "Proper Diagnosis of S-cam Out-of-service Criteria," at the annual meeting of the ATA's Technology & Maintenance Council meeting in Atlanta. The task force committee were refining the wording of the RP.

Ever since automatic brake adjusters (ABA) were first required by law in 1994, many drivers and surprisingly, brake technicians still respond to an over-stroking S-cam brake by manually readjusting the device rather than determining the root cause of the problem. By design, an ABA will self-adjust based on either the application stroke (stroke sensing ABA models) or the return stroke (clearance sensing ABA models) of the adjuster and find their own stroke length based on the conditions it senses. Unfortunately, a manually readjusted ABA will return to an over-stroke condition in just a few brake applications if some other physical problem exists with the foundation brake, the parking brake or any other component in the wheel-end brake assembly.

This RP will walk the technician through a troubleshooting tree that will determine the cause of the over-stroke so appropriate steps can be taken to solve the problem.

"All too often, the root cause of the excessive applied stroke condition is not diagnosed properly," said task force chairman, Glen Cram of Meritor. "it became clear during our research that no publication out there in the industry really gives the technician a clear-cut way to determine how to diagnose this problem."

When complete, the RP will take the technician through an eight-step process from confirming that an over-stroke condition ...Read the rest of this story

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Eco Flaps Tested on LTL Equipment

Eco Flaps Splash Guard Photo: Eco Flaps

The Eco Flaps aerodynamic splash guards were recently evaluated for fuel savings on less than truckload equipment in multi-trailer setups.

The tests were completed by Exa Corporation in late 2017, performing an aerodynamics and fuel economy analysis through computational fluid dynamics simulations on a day cab tractor with two 28-foot trailers connected by a dolly. It found an estimated 2.7% fuel savings based on the reduction in drag.

"The segment of the trucking industry that run with two or three trailers at a time, which includes most LTL carriers, is really limited when it comes to aerodynamic devices. Most are designed specifically for single-trailer application," said Bren Marshell, vice president of sales for Eco Flaps. "Our recent work with Exa Corporation shows that when Eco Flaps are installed in all flap positions on multiple trailers, drag is reduced significantly, resulting in greater fuel savings and quick ROI."

Exa Corporation created four different scenarios: a baseline with conventional flaps; changing out the truck and dolly flaps for Eco Flaps; a full swap out of all eight flaps for Eco Flaps; and an equipment setup with no flaps used. The results showed a 4.7% improvement in drag at highway speeds when all eight flaps were removed - even though the pup trailers already using aerodynamic skirts. The use of eight Eco Flaps - a full swap out - created the same results.

"The Exa Corporation simulations showed a major impact when equipping the dolly flaps in addition with the tractor and trailers," said Marshell. "Not including the dolly greatly restricts the airflow and thereby significantly reduces fuel savings from the leading trailers."

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