At the fall meeting of the Technology and Maintenance Council, one highly enjoyable session looked, quite intentionally, like an episode of TV’s “Antiques Roadshow.” You know the show. People bring in old heirlooms and personal treasures. An expert tells them where the items came from, how old they are and what they’re worth.
At this roadshow, fleet managers brought in failed vehicle components, and it was the job of panelists and the audience to examine them and determine what caused the failures. As any savvy fleet operator knows, if you don’t know what caused a failure, you can’t stop it from happening again. Here are some “clips” from the latest episode of TMC’s “Failure Analysis Roadshow”:
Off the hook
The broken pintle hook assembly in Photos 1 & 2 looks at first like a casting or metallurgy defect. The gray, granular appearance of the metal at the break indicates that the assembly parted company during a single event. Absent are “beach” marks – concentric, elliptical lines that accompany fatigue, a process in which repeated, smaller events cause cracks that gradually deepen.
A panelist determined that this failure was caused by a driver attempting to back a doubles rig without first ensuring that the brakes on the second trailer were released. This caused the dolly drawbar to want to “walk up” the back of the lead trailer. The unfortunate pintle hook assembly proved no match for the drawbar and determined driver.
Just a case of neglect?
The oil cooler heat-exchanger pickup and cylinder liner in Photos 3 & 4 could quickly be dismissed as victims of gross negligence. One might conclude that there was little or no cooling-system maintenance over a long period of time and many miles. Severe rust and scale on the pickup, and rust and deep pitting on the cylinder liner could suggest that the system was run without benefit of corrosion inhibitors, or even antifreeze.
But not so fast. This was a fairly low-mileage engine that had, according to shop records, been very well maintained. Hmmm.
Tough problems often require extreme measures. Although a detailed chemical analysis is not usually part of any cooling-system check, Darrell Hicks, national OEM manager for The Penray Companies in Maumelle, Ark., had one performed on this engine’s coolant.
What the analysis found would make even the most adventurous sous-chef wince. The coolant sample showed that about two pounds of salt had been added to the cooling system. Sabotage! Perhaps by a disgruntled employee or garden-variety vandal. Builds a good case for hood locks, doesn’t it?
What damaged the brake lining?
Rust never sleeps
The brake lining in Photo 5 looks like it could have been severely overheated. But the drum revealed no telltale heat-checking or bluing.
Removal of the mating shoe’s lining revealed prolific rusting (Photo 6) – enough to cause surface irregularities of nearly 1/4 inch. As the brakes were applied, the linings were repeatedly pushed against the drum with uneven pressure across the shoe table, causing the linings to crack over the edges of the high spots.
This process, called “rust jacking,” is becoming more pronounced, noted panelists. While it is more often found in shoes that have been relined without being properly prepared and painted, it can occur in OE shoes as well.
Increased incidence of rust damage in brakes and other components can be traced to new chemicals used to melt snow and ice on our roadways. TMC devoted a separate session to the problem at its fall meeting.
While plain old salt does a good job melting ice and snow (and corroding metal), highway departments have discovered that other compounds – calcium chloride and magnesium chloride, for example – do a better melting job and are far cheaper. They are also far more corrosive.
Rust problems also have been exacerbated by the introduction of long-life brakes, according to Roy Gambrell, director of maintenance for Truck-It Inc. in Franklin, Ky. “The linings last longer,” he acknowledges. “But that means brake shoes spend a longer time exposed to the elements.” The situation probably will get worse as more snow-prone states discover that they can clear roads faster and save money by using the new chemicals.
What can a fleet operator do to minimize rust jacking? For starters, said panelists, visit the shop that produces your relined brake shoes. Make sure they properly measure shoes for conformity and discard those that don’t make the grade. Look at surface-preparation, painting and riveting techniques. Shoe tables should be smooth and protected from corrosion before linings are installed. Rivets should be tight, and linings firmly and uniformly in contact with the entire shoe table, with no movement possible.
Finally, although he admits he’s no fan of brake dust-shields, Darry Stuart of Transportation & Fleet Management Resources in Wrentham, Mass., revealed that all the Pennsylvania snow-belt truck fleets he inspected had rust-jacking problems – except one. “That one used dust shields,” Stuart says.
Fleet managers were as fascinated with TMC’s “Failure Analysis Roadshow” as antiquers are with its television counterpart. The roadshow has already become a regular feature in the TMC lineup.