Maintenance Q&A
Shimmies and squeaks

By Paul Abelson, Land Line senior technical editor

I recently bought a brand-new Kenworth. Almost immediately, I started to feel a shimmy. I took the truck back to the dealer. They balanced the steer tires and aligned the truck. That didn't help. By the time I got a few thousand miles on it, the vibration was pretty severe.

I brought it back in to the dealer. My dealer checked the hubs to see if they were causing or contributing to the problem. The hubs were all well within tolerance at 0.003 inches or less. The Meritor X30 drums should have been at 0.02 or less. However, some were measured at 0.028. The dealer acquired replacement drums, mounted them, and I went on my way.

The vibration was still there. When I got back, the dealer measured the new drums and found 0.024 to 0.032 run out. The dealer installed a second set of replacements. Come to find out some of those were out of spec.

After you alerted OOIDA and Land Line to your problem, we contacted Meritor directly and your problem was quickly resolved.

However, it's important to note that there are two takeaways from a situation like this.

First, just because a part is replaced - even with an OEM or aftermarket part - does not guarantee the problem is solved. Suppliers all the way to the second- and third-tier can have problems.

Second, just because someone tells you he's done all that could be done and you'll have to live with the situation, don't believe it. There are always paths up the chain of command to the manufacturers.

In this instance, Meritor took the problem seriously as soon as we alerted them and made things right straight away. The member reports that the vibration is gone and the truck rides as well as any he has owned. He is happy with the results.

If you have trouble getting "to the top," anyone can use the resources open to them in the trucking industry - OOIDA, Technology and Maintenance Council and others. As with all reputable suppliers and OEMs, Meritor said all customer complaints are taken very seriously.

Specific to this situation, Meritor reminded us that with the reduced stopping distances now required, the entire brake system is under far more stress, and certain tolerances are more critical than ever before.

This summer, my fan belt started squeaking. I changed the belt. It surprised me how expensive those all-in-one belts are. A few weeks later, the squeaking came back. I thought it might have been caused by the air conditioner, but it comes and goes even with the air conditioner off. Should I replace the belt again or is there something else that went wrong?

I agree that the new poly-V belts are expensive, but there are reasons. Belts with multiple grooves do more work than the old V-belts. They need to be stronger and tougher. Under-hood temperatures are far greater with the EPA-era engines equipped with exhaust gas recirculation, so the compounds in the belts must be more temperature resistant. But to understand what contributed to your belt squeal and why the poly-V belts are better, let's look at how a belt functions.

Accessory-drive belts have V-shapes that sit in similarly shaped pulleys. Friction between the tapered sides of the belt and the sides of the pulleys transmits power to the belt and from it to the accessory being driven. The diameter of the pulleys varies from outside to inside, causing partial slippage. Over time, this wears the rubber-like material, usually a synthetic like Neoprene or EPDM (ethylene propylene diene monomer). These have different wear patterns.

Neoprene wear is more obvious, with visible cracks and chunks of ribs missing from the working face. This starts after as little as 50,000 miles. EPDM belts may not show visible wear until well over 100,000 miles, but that doesn't mean they don't wear. The wear causes loss of traction as belts slip. That causes the squeak or squeal you hear when load, such as an air conditioner compressor clutch coming on, is added to the drive belt. Air conditioning works with defrosters, so you can get squeal whenever the HVAC system operates.

Slip can also increase belt temperatures up to 50 percent. Heat flows through pulleys to accessories, leading to bearing failures. When a worn belt bottoms out on a pulley, any splash or spray can cause a belt to hydroplane and lose drive traction. And normal belt stretch over time can loosen contact with pulleys eventually causing accessories to fail. To compensate, automatic belt tensioners help maintain proper tension on the belt. They should be replaced every time a belt is changed because their springs lose tension over time.

TMC has a Recommended Practice, RP320C, Inspection, Maintenance and Tension of Accessory Belt Drive Systems. Gates Rubber offers a pocket gauge on its web page. It's about the size of a loyal shopper tag that fits on a key chain. Just fit it into the grooves on the belt. If you can wiggle it, replace the belt. If not, you're good to go. Finally, always make sure pulleys are in alignment when replacing belts. That's a significant contributor to belt wear. LL