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Maintenance Q&A
Maintenance Q&A

By Paul Abelson
senior techincal editor


Q: Has Freightliner changed something in its windshields? My 2006 Columbia had three cracks in less than a year. What can I do to stop this?

A: Unfortunately, not much. On your Columbia, the windshield is bonded to its frame. It becomes a structural part of the cab, helping to resist twisting and flexing. It also helps support the roof.

Replacing windshields has become more complicated than it was before we had an understanding of the structural role of glass.

There is a comprehensive Technology & Maintenance Council Recommended Practice, RP 429 Windshield Replacement and Repair, which was written by OOIDA member Gail Bristow.

The old way of mounting windshields, with rope gaskets, allowed the windshield to float in its frame. It wasn’t as highly stressed.

With bonded windshields anything that alters the surface integrity of the glass, such as a stone chip, can be a stress point that can initiate a catastrophic failure. You could hit a bump or pothole, and the cab flexing will crack or even shatter the glass starting at the point of damage.

If you have a choice, opt for a two-piece gasketed windshield. An advantage of two-piece windshields is that when they do crack, it’s easier and cheaper to replace only one side at a time.

Q: This winter, the air filters on my 2004 International collapsed after only 15,000 to 18,000 miles. I use a filter gauge and had been getting more than 75,000 miles last summer.

 Now, the gauge hasn’t even started to read high, but all of a sudden the engine has started smoking black and it has lost power big time. The filter just got sucked in. It happened twice. What can I do?

A: When we spoke in greater detail about your problem, you mentioned you ran from Chicago to London and Toronto, Ontario, all year long. The problem started in December when the snows came. All along your route, the various highway departments use aggressive snow removal chemicals, and that provides a possible answer.

Unfortunately, yours is not an isolated case. A number of TMC members complained about collapsed air filters at this year’s annual meeting in February. It seems that the new chloride mixtures go into the solution with the water from the snow. Tires throw spray into the air where it gets sucked into the air intakes and into the filters. The filters absorb and hold the salts.

As the water evaporates, crystals build up on the filter surfaces. Eventually, they weaken the paper and choke off the airflow. Then the vacuum, drawn by your twin-turbo Cat engine, overcomes the filter frame’s ability to resist.

Your Filter Minder probably detected the increased resistance, but you have an underhood gauge, not a dashboard readout. Because the increase was so accelerated, you weren’t alerted to look for it and didn’t notice.

A maintenance director I know had a driver call in that his truck lost power and started smoking. He told the driver to remove the air filter, which restored power. The driver bought a replacement at the next truck stop.

Next winter, keep an extra air filter in your truck. It will probably happen again.

Q: Another driver from my company told me that one of my trailer tires was going flat. When he passed me on the Interstate, he heard that telltale “whup-whup-whup” that soft tires make. But when I gauged my tires, they were all at 95 psi or more.

We traded seats until the next rest area, and I heard it too when I drove his truck past my trailer. If my tires aren’t soft, what is causing the noise?

A: There are many things that can generate that distinctive sound, or something close to it. Uneven wear, such as cupping or diagonal wear will also generate noise, especially when coupled with lack of shock absorber control.

The TMC publishes the “Radial Tire Conditions Analysis Guide.” It’s also included in the Recommended Practices Manual that you get free with an owner-operator membership in TMC. The guide illustrates three types of unusual trailer tire wear: diagonal wear, multiple flat spotting wear and erratic depression wear.

Diagonal wear has localized flat spots worn across the tread at about 25 to 35 degree angles. They are often repeated across the tread. Multiple flat spotting is similar, but the pattern is around the circumference of the tread. Erratic depressions are random, not regular. There are several common causes, and some causes unique to each.

Wheel hub bearings out of adjustment coupled with worn shock absorbers can contribute to erratic wear and multiple flat spotting. Mismatched air pressures between dual tires will intensify all three conditions. A flat spot caused by a locked wheel, possibly because of using the trolley valve, can start the uneven wear process, especially when operating with light loads at high speeds. With worn shocks, tires bounce. Trailers that bogie out of line and shifted axles can also contribute to diagonal wear.

Correct the cause of the unusual wear, and continue to use the tires unless wear is excessive. Remember, you measure at the area of minimum tread depth, not maximum. If the tire casing is otherwise undamaged, you may want to salvage a tire with deeper tread by truing it on a tire lathe. Diagonal wear can be reduced by reversing the direction of rotation. Retreading, which involves turning and buffing the tire, removes tread problems and, in today’s economy, should be considered as an alternative to new tires. LL

Paul Abelson can be reached