Wheel covers, air dryers and alternators

May 2019

Paul Abelson


  1. Q. This is going to seem weird, but is there a relationship between aerodynamics and truck stability? I ask because last August I put flat, aerodynamic wheel covers on my drive wheels to cover the deep dish. Lately, my truck seems to wander a lot more, especially when I’m braking. I’ve had it before but never this bad. My truck is a 2014 Cascadia with an automated transmission. Is there something going on I should know about, something they discovered or something I can do?A. Your question is far from weird. In fact, it represents one of a number of problems observed since the introduction of aerodynamic wheel covers a few of years ago. These prompted TMC to study the situation and issue a recommended practice on the subject, RP261. The wheel covers do improve fuel economy but may have unintended consequences on wear and maintenance. Some covers are transparent, allowing easy observation of wheel hubs and lug nuts. Others must be removed for inspection of these critical components, either of which could lead to what you describe as “wander.”

    While they smooth airflow on the outside of the wheels, they may restrict the flow of cooling air to the brake drums. This may result in uneven drum heating, leading to what you feel as wander or a tendency to drift from side to side under braking. Disc brakes lessen this tendency to wander but don’t fully correct it.

    If wheel ends are not regularly inspected for proper lubrication, one end could drag more, resulting in the perception of wander. It could loosen lug nuts that cause enlargement of bolt holes, especially in aluminum wheels. A loosening wheel could also feel like wander.

    Q. I own a 2016 Mack Pinnacle with all Mack running gear. A few weeks ago, I started noticing water coming out of the spitter valve near the drives. I changed the cartridge in my air dryer when I winterized in October. I’ve been trucking for more than 20 years, and this is the first time I’ve seen more than a few drips come out. Did my dealer sell me a defective dryer?

    A. The first thing you did was go back to the dealer, and he checked his records and assured you that you got genuine original equipment manufacturer parts. This matters because some offshore or bargain-priced cartridges may not have the right quantity or type of desiccant material and may not have oil-coalescing material. Knockoff products also may be poorly machined and may not seat properly. It always amazes me that someone with well over $100,000 invested in a truck will try to save $5 to $10 on parts crucial to the truck’s safe, reliable operation.

    First, make sure the cartridge was properly installed and that all gaskets are seated well. Then check all air lines and connections for damage and tightness. With the system at full pressure, listen for leaks. Make sure the discharge line from the compressor to the dryer slopes continuously downward. An arc in the line could trap condensed water. Even if it doesn’t freeze, it can restrict air flow.

    Some water condensation may be due to changes in ambient temperature, especially if greater than 30 degrees. The excess moisture expelled may just be temporary, caused by the temperature change.

    In severe cold, drain the tanks daily. It’s not so much to make sure water doesn’t accumulate (not a good thing) in the tanks but to make sure the valves operate properly.

    Unless the system is actually frozen, avoid adding alcohol or de-icing solutions that contain alcohol. Any components downstream of where the alcohol is introduced, especially seals, may be attacked by the alcohol. If it’s used, check for leaks at O-ring seals and valves. If leaks are found, you may have to replace the O-ring and possibly the valve.

    Q. I own a 2010 Peterbilt with Cummins 500 power. In the past year, I replaced two alternators with rebuilds, and it looks like I’m going to need another one soon. Should I get a higher amp alternator? Do I need to go with a factory new one instead of a rebuilt? What do you advise?

    A. There are many factors that affect alternator life, including the quality of the rebuild and the loads put on the alternator. Before looking to replace another one, first check external things that affect its performance. Remember, the first rule of maintenance is that if all you do is replace the affected part, you’ll replace it again and again. But if you find the cause and correct that, you’ll never have to worry about it again (except for normal wear).

    Before replacing another alternator, check all wiring, including heavy-duty cables, for abrasion, corrosion and tightness of all connections. Cycling from hot to cold and regular truck vibration can loosen fasteners and connections. Check for voltage drop that can signal internal damage in wiring. Pay special attention to connections at the battery and starter. Make sure the battery is capable of holding the charge sent to it. According to TMC RP129, voltage drop in the charging and starting system should be no more than half a volt (0.5v). To maintain proper connections, torque all fasteners as published in your owner’s manual. If that’s not handy, check with your dealer.

    Be sure the alternator’s fan is free of dirt and debris. They can accumulate and block cooling, lowering the alternator’s efficiency.

    If you’ve altered your operations in a way that would increase alternator work load, such as increasing urban stop-and-go driving, or if you added electric idle reduction or hotel loads, consider increasing alternator amperage. Not having enough amps stresses the alternator and weakens batteries, while increased output reduces stress and prolongs life.

    Most rebuilt alternators are brought up to original equipment manufacturer output specifications, but I believe remanufactured units using OEM parts are a safer bet. Remanufacturing offers better quality control and stronger warranties. LL


Paul Abelson, senior technical consultant, is a longtime contributor to Land Line. He’s a member of the Society of Automotive Engineers and a member of the Technology and Maintenance Council. In 1995, TMC awarded him its Silver Spark Plug award. In 2006, he received the Lifetime Achievement Award from the Truck Writers of North America. Although he’s “retired,” he still makes a popular contribution to Land Line readers with “Maintenance Q and A.”