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Rust Jacking

Rust Jacking

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    An aluminum fuel tank and parking brake springs show signs of rust jacking.

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    Rust forms an A-shaped wedge that jacks up the brake shoe, which then cracks under the jacking force of the rust.

Ready-mix trucks and any other equipment you operate when highways and streets have been treated with snow and ice removal chemicals will be susceptible to rust and corrosion as never before.

Roy Gambrell, maintenance director for Truck It, a small trucking company in Franklin, Ky., and a member of the board of directors of the Technology and Maintenance Council (TMC), was the first to identify “rust jacking” and bring it to the trucking industry's attention.

When investigating brake shoe failures after only 18 months of over-the-road service, he noticed edge cracks in his brake linings that initially looked like heat damage. Eventually, the cracks deepened enough to put the units out of service. When Gambrell pulled his wheels, the cracks went clear across the brake shoes.

He removed the shoes and found rust build-up as high as ¼ inch on the shoe tables. Rust forms an A-shaped wedge that literally jacks up the brake shoe. Held in place by rivets, the shoes crack under the jacking force of the rust, just as expanding ice can crack the steel hull of a ship.

TMC began an investigation. Members found premature rusting was destroying equipment at a rate never seen before. Damage was not confined to brakes. Virtually any unprotected metal is affected, including steel, iron, and aluminum. Paint protects metals, but if the integrity of the paint is broken by a scratch or a stone chip, a path opens for rusting to start.

The culprit

The sudden increase in rust damage is directly traceable to the increasing use of aggressive snow removal and deicing chemicals in northern states. Previously, most states used rock salt (sodium chloride), sometimes mixed with sand or cinders for traction. In the late 1990s, state and local road and transportation departments started experimenting with more aggressive chemicals: calcium chloride and magnesium chloride, often in combination with each other or with rock salt, and with potassium acetate and calcium-magnesium acetate.

Before the advent of these chemicals, snowplows were stationed along the roads in anticipation of forecasted snow. If and when the snow reached a pre-determined depth, the trucks started to plow and spread salt. It took fuel to idle the engines, and lots of overtime to keep the workers in position.

Today, chemicals are spread in advance of snow or ice storms, often dissolved in water and sprayed on roads several hours before they may be needed. In theory, they dry to an even coat and then start working after the snow falls. Trucks and personnel need not be present.

In the real world, the aggressive liquid chlorides and acetates stay on the pavement only until they are kicked up by car and truck tires as spray. The spray permeates the air and deposits on all vehicles driving through these mists. Once the chemicals find a weakness, even in recesses as hidden as the crevices between the brake shoe and the table, corrosion starts.

Preventing rust

As bad as this sounds, there are ways to prevent excessive rust damage short of refusing to drive north of Interstate 10. First, keep your truck clean, especially after driving through brine sprays. Look for the pervasive film on your windshield, lights, and reflectors. Most washer fluid isn't strong enough to dissolve it, and when it builds up on headlamps, their range is shortened. Pressure washing, especially the undercarriage and beneath the truck, will cut through the build-up and remove the chemicals to prevent much of the damage.