Even aluminum can corrode, as damaged fuel tank shows.
During routine truck inspections a few years ago, Roy Gambrell was alarmed to notice pronounced cracking – bad enough for an out-of-service citation – on brake-shoe linings that were only 30 to 35 percent worn. “Usually, you think of lining cracking as a heat problem generated by imbalanced brakes,” says Gambrell, director of maintenance for Franklin, Ky.-based Truck-It Inc. “But we don’t have imbalance issues. I knew it was something else.”
Don’t want no rust, Jack
The problem turned out to be a relatively new phenomenon called rust jacking – a process wherein brake shoe tables rust severely under the linings, causing surface irregularities of nearly 1/4 inch. As the brakes are applied, the linings repeatedly are pushed against the drum with uneven pressure across the shoe table, causing the linings to crack over the edges of the high spots.
The root cause? While good old salt always has done a good job melting ice and snow – and, unfortunately, corroding metal – highway departments in snow-prone states have discovered that other compounds such as calcium chloride and magnesium chloride do a better melting job, and are far cheaper. They also are far more corrosive, often to critical vehicle safety components like brakes.
This condition is found most often in shoes that have been relined without being prepared and painted properly, but it does occur in OE shoes as well. Even with brand new shoes, “I still have to discard them with about 30 percent wear left on them,” says Gambrell. And the problem has gotten worse with the introduction of long-life brakes. “The linings last longer,” he acknowledges. “But that means brake shoes spend a longer time exposed to the elements.”
No component safe
“It’s been tough getting people to realize the damage this stuff can do,” says Gambrell. “Even to tires. Think about it – if there’s a small nick in the tread, these chemicals can wick their way up to the steel belts and corrode them.”
And it’s not just steel or other ferrous alloys that get attacked. “I’ve seen holes eaten in aluminum fuel tanks,” he attests. “No part on a truck is safe.”
