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When Tires and Patience Wear Thin

November 05, 1987|RALPH VARTABEDIAN | Times Staff Writer

Question: I drive a 1976 Chevrolet Van, modified into a camper with some extra weight. As a result, I am always operating near the high end of the vehicle's allowable gross weight. The front tires have consistently worn smooth on the inside edges, the sign of underinflation. I have changed from belted to radial tires and had the front end aligned, but I see no change in the abnormal wear. Any suggestions?--C.R.

Answer: The wear pattern you describe can indeed be caused by a front end that has a bad alignment. And although you have had the front end aligned several times, if an abnormal-wear pattern was established on the tires before the alignment it will probably continue after the alignment is corrected. This is why it is important to rotate tires, if you haven't already done so.

Assuming the van is properly aligned and the tires are still wearing prematurely, you have several options. You might consider looking for a wider tire, which would distribute the vehicle's544695657section of the tire. The new metric tire-sizing system should make it an easy job, because the width of the tire is part of the size. For example, P-225-70-13 means a tire has a width of 225 millimeters, its width is 70% of its radius and it fits on a 13-inch wheel.

If you change tire sizes, I advise you find a garage that is familiar with such work. Before making the decision, you should have the front and rear of the vehicle weighed to see how much you have changed the weight distribution. You may want to call a tire manufacturer and ask for the engineering or product-information department, which may help you find a new size.

You'll want to select a wider-profile tire, but one that has about the same diameter. The new sizing system gives you a great deal of flexibility. In some cases, you could go to a different wheel size and alter the aspect ratio and get a much wider tire that has the same diameter as the original tire.

Q: When I drive my 1984 Stanza downhill in first gear, it frequently shifts itself into neutral. This happened occasionally when it was a new car, but now it happens often. Nissan thinks it has something to do with the transmission. Any advice?--S.S.

A: The problem probably is that a part called a blocking ring has worn out inside your transmission. A block ring is a small brass part that is associated with the synchronizer assembly inside the transmission. The synchronizer is the system that allows the gears to be downshifted even though the car is in motion. It does this by equalizing the speed of different sets of gears or shafts so they can mesh together.

Your transmission is popping out of gear because when you decelerate hard, such as when using first gear going downhill, you put a lot of pressure on the blocking ring. When shifting up or accelerating, there is much less pressure on that brass ring.

This raises a new question. Why are you going downhill in first gear? Possibly, you are putting a lot more stress on your engine and transmission than you need to. Typically, the first gear would not be used at speeds more than 15 m.p.h., which is slow enough that it would be far better to just use your brakes. If the condition gets any worse or the transmission fails, you'll need to rebuild the transmission at a cost of hundreds of dollars.

You should also contact Nissan headquarters. If the problem started while the car was under warranty and you can prove that point, the company may be willing to fix it. The headquarters for Nissan USA is at 18501 S. Figueroa St., Carson, Calif. 90248-4504.

Ralph Vartabedian cannot answer mail personally but will respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, You section, The Times, Times Mirror Square, Los Angeles 90053.

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