At the Technology and Maintenance Council (TMC) Annual Meeting back in 2001, Roy Gambrell shocked the truck maintenance community by making us all aware of a new phenomenon - rust jacking. Roy is director of maintenance for Truck It, a small fleet in Franklin, Ky. He is also vice chairman of TMC and will be general chairman for 2011-2012.
Roy found that his fleet's brake linings were cracking after only 30,000 to 40,000 miles of over-the-road service instead of his getting his usual 100,000 miles or more. When shoes had been repaired or replaced, especially with low-priced aftermarket parts, the cracking was found to occur even more rapidly.
The cause was rust jacking, a phenomenon that occurs after our trucks run on roads where corrosive chemicals have been applied to prevent or control snow and ice. As tires roll, they kick up fine sprays of the chemicals. The moisture carries sodium chloride, calcium chloride, and magnesium chloride, often in combination. It gets into the nooks and crannies of our trucks' structures.
When spray and chemicals get onto the steel brake shoes, they cause rust. Rust, or iron oxide, expands to a greater volume than the original iron because it combines with oxygen. That expanded material has nowhere to go, so it presses outward against the weakest point of resistance, the brake linings. Eventually the pressure becomes great enough to crack the linings. If caught early, the cracked linings will just put a truck out of service. If not caught in time, brakes can fail catastrophically. That means crashes.
A pervasive problem
Darry Stuart, president of DWS Fleet Management Services, has photographic evidence that demonstrates how widespread corrosion has become. Stuart's photos show that virtually anywhere metal is exposed, it can be attacked. Suspension parts are abraded by sand and gravel, as are painted aluminum and steel fuel tanks, landing gear, cab steps, and even cross members and chassis rails. They often rust enough to lose all structural strength.
Corrosion isn't confined to structural parts. Air line connections deteriorate and will no longer hold air. Tank straps and related hardware can no longer support the tanks. Hose end fittings have been found to be so corroded, they can no longer keep hoses attached, and brake air chambers have rusted through so brakes no longer work. Imagine coming down your steepest grade with one or more brake chambers rusted through and not working.
The nature of these chemicals is that, in vapor-borne solution, they wick into joints between two metal surfaces. There they stay, even through numerous washings. Magnesium chloride is one of the worst offenders. While less aggressive than ordinary road salt, magnesium chloride retains water, even drawing humidity from the air. It does more total damage over time than plain salt. If relative humidity is above 27%, magnesium chloride will stay wet continuously.
Fighting corrosive forces
While many 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 the cracks. You may have to disassemble components to get to where the rust starts. Sprays and paints that chemically convert rust into phosphates are a good stop-gap measure, preventing additional rust formation. For a long-term fix, abrade or sand blast down to bare metal. Then prime and paint.
Many fleets pay thousands of extra dollars up front to get galvanized or even stainless steel components, or powder-coated rather than painted replacements. Long-life components pay for themselves many times over, especially on a vehicle subjected to the abuse a mixer endures. If your equipment doesn't have these long-life components, consider them when it's time to replace parts.
When performing maintenance, use the best quality products you can get. 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 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.
Long vehicle life starts with specifying the best components. Make sure they're suitable for the job, then consider corrosion protection. This applies more to replacement parts than for new ones. Original equipment manufacturers generally use parts tested for suitability to their tasks.
The next step in fighting corrosion is cleanliness. It's a good idea to wash every truck regularly. When cleaning out drums, hose down the cab and chassis to flush away any corrosives. During salt spray season, wash more often. Pressure washing works well on sides and tops, but around the undercarriage, it forces corrosive chemicals deeper into crevices. High volume flooding may be more effective. After washing and during your pre-trip inspections, check for any signs of rust or galvanic action between metal parts.
Take your time. Be thorough in all you do: specification selection, cleaning, painting, inspecting, and repairing. You'll get the longest possible life from your rolling stock. Click here for Part I: Protecting Your Assets