Tracking Down Another Automotive Pest: The Intermittent Rattle
Question: My Honda Accord has a rattle that is driving me nuts. It occurs only at about 2,000 rpm engine speed and seems to be coming from beneath the car or from the front end. It doesn’t do it all the time, either. It sounds like one part is vibrating against another part. My mechanic suggests it might be the catalytic converter, but he isn’t sure. I don’t want to drop a bundle on a guess. Any ideas? --T.T.
Answer: Rattles that occur only intermittently when the car is in motion are indeed curses, because they can be impossible to eliminate.
The first step is to have the car inspected carefully for loose parts, both inside the engine compartment and from below. Heat shields, which are flimsy pieces of sheet metal, are often the culprit, because they vibrate against other parts or simply vibrate by themselves, creating a tremendous racket.
Another suspect item is the hood itself. Parts inside the engine have a way of vibrating against the underside of the hood, which acts like a percussion instrument, amplifying the sound of the most harmless rubbing.
A Honda’s engine compartment is packed full and there are a lot of parts that ride close to the hood. Look carefully at the inside of the hood to see if you can find any spots where rubbing may be occurring.
You can, indeed, drop a bundle of money if you start replacing parts based on guesses as to what may be wrong.
Q: I have a 1993 Ford Tempo. The left front brake pads wear out twice as fast as the right pads (8,000 to 10,000 miles). Someone told me that the caliper might be sticking. I have changed both calipers twice to no avail. Could it be the master cylinder? --J.Q.
A: You definitely have a problem if you’re eating up an entire brake pad in 8,000 miles. It should have been easy enough to determine if the caliper was sticking without going to the expense of replacing it once, let alone twice.
There are other possibilities, including a warped disk, which would also cause a pulsing sensation when you apply the brakes. Or it could be a problem with one of the brake system metering valves, causing it to apply too much hydraulic pressure to that brake.
The problem is probably not the master cylinder, although a good brake mechanic would examine that, along with all the other key components in the system.
Q: My local Firestone dealer mailed a coupon for a free tire rotation and inspection. When I decided to take advantage of the free offer, I found that the front left tire was swapped for the rear left and the front right swapped for the rear right. Is this correct? The owner’s manual suggests an X pattern rotation, in which the left front tire goes to the right rear, etc. --S.N.
A: The dealer should have discussed the rotation pattern with you before doing anything and should have consulted the owners manual.
Seldom does an independent shop or tire dealership know everything contained in an owner’s manual. Yet often, recommendations on things such as rotation and tire pressure matter a lot to vehicle safety.
Tire-rotation practices have changed a lot. An X pattern rotation was normal for decades, until the early days of radial tires. Then, many manufacturers recommended against the X pattern. A tire going from the right front to the left rear, for example, changes direction of rotation and there was great concern that such a change could weaken the structure of the tire.
Most tire makers no longer warn against X pattern rotations, however. The whole point of tire rotation is to change the wear pattern, and that is maximized by going with the X. The exception is for uni-directional tires, usually mounted on high-performance cars such as the Chevrolet Corvette. These tires are designed to roll in only one direction and should never be swapped in an X pattern.
So there’s nothing wrong with the rotation you received. But after several thousand miles, it would make sense to rotate the tires again, following the recommendations in your owner’s manual.
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Ralph Vartabedian cannot answer mail personally but responds in this column to automotive questions of general interest. Please do not telephone. Write to Your Wheels, Business Section, Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012. E-mail: ralph.vartabedian@latimes.com.
