Launch Slideshow

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Chemical reactions

Chemical reactions

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    Rust-jacked brake linings, top and side views. Photos: TMC/Roy Gambrell and Darry Stewart.

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    This glad hand fitting is beyond repair.

By: Paul Abelson

Editor's note: Last month, we began our examination of the effects of snow and ice control chemicals on cabs and hardware. We continue our series with combating corrosion on chassis, suspensions, and brakes.

In 2001, Roy Gambrell shocked attendees of the American Trucking Associations' Technology and Maintenance Council Annual Meeting by making us aware of a new phenomenon.

Gambrell is maintenance director for Truck It in Franklin, Ky., and the council's soon-to-be general chairman. He'd found that his fleet's brake linings were cracking after only 30,000 to 40,000 miles instead of the 100,000 miles or more he'd been getting. When shoes were repaired or replaced, the cracking occurred more rapidly.













The cause: chemicals applied to roads to prevent or control snow and ice. As tires roll over the roads they kick up fine sprays of the chemicals. The moisture carries sodium chloride, calcium chloride, and magnesium chloride, often in combination, which wicks into the vehicle's nooks, crannies, and joints between metal surfaces. And there they stay, even through numerous washings.

When they get onto the steel brake shoes, they cause rust.

Rust, or iron oxide, expands to a greater volume than the original iron it combines with. The expanded material has nowhere to go, so it presses outward against the weakest point of resistance: the linings. Eventually the pressure cracks the linings. If caught early, the cracks will put a truck out of service. If not caught in time, brakes fail catastrophically. That causes crashes.

Magnesium chloride is one of the worst offenders. While less aggressive than ordinary road salt, magnesium chloride retains water — even drawing water from the air — to do more total damage over time. If relative humidity is more than 27%, magnesium chloride stays wet continuously.

Shortly after Gambrell identified “rust jacking,” Darry Stuart, president of DWS Fleet Management Services, Wrentham, Mass., presented photographic evidence demonstrating how widespread corrosion had become. Brake shoes aren't the only victims. Virtually all exposed metal on a truck— suspension parts, painted aluminum and steel fuel tanks, landing gear, cab steps, and even cross members and chassis rails — can rust enough to lose all structural strength.

Corrosion isn't confined to structural parts. Line connections deteriorate and no longer hold air. Straps and related hardware no longer support tanks. End fittings no longer keep hoses attached, and air chambers rust through so that brakes won't work.

COUNTER-ATTACK MEASURES

Long vehicle life starts with specifying the best components. Some managers pay thousands up front for galvanized and stainless-steel components, which pay for themselves many times over the life of a vehicle. Make sure they're suitable for the job, then consider corrosion protection.

That applies to replacement parts as well. Inexpensive brake shoes that you replace four times a year, or suspension hangers that rust through, are no bargain. Powder-coated products have epoxy or urethane resins that are drawn to surfaces with electrostatic charges and then baked to melt and flow the particles into all nooks and crannies. They provide the longest coating life, even in the most adverse conditions.

The next step in fighting corrosion is cleanliness.

While surfaces may look damage-free, they may be rusting from inside out, often in the spaces between metals. At the first sign of corrosion on the surface, clean whatever you can. Then, try to inspect and clean in the cracks. You may have to disassemble components to get where the rust starts. Sprays and paints that chemically convert rust into phosphates are good stop-gap measures to prevent additional rust formation, but for a long-term fix, abrade or sandblast down to bare metal. Then prime and paint.

Wash trucks regularly and more often during winter. Pressure washing works well on sides and tops, but because it forces corrosive chemicals deeper into undercarriage crevices, high-volume flooding may be more effective. After washing and during pre-trip inspections, check for signs of rust or galvanic action between metal parts.

Take your time. Be thorough in all you do. You'll get the longest possible life from all your rolling stock.

— Paul Abelson (truckwriter@anet.com) is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.