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Getting In Gear Over Bad Transmission

February 27, 1986|RALPH VARTABEDIAN | Times Staff Writer

Question: I own a 1982 Corvette with a special four-speed automatic transmission. The car lugs and the engine rpm's drop below 1,000 when the car shifts. At 39,000 miles, the first gear became ground metal, resulting in a $1,500 bill for a new transmission. I don't want to repeat the problem. What's wrong?--J.M.W.

Answer: Your problem, in a broad sense, is that General Motors produced a lot of bad transmissions in the late 1970s and early 1980s. Thousands of General Motors car owners have had to lay out huge sums of money for one or more transmission overhauls.

I had the opportunity recently to ask General Motors Chairman Roger Smith about the transmissions. He said GM has invested more than $100 million to improve manufacturing processes at its Hydra-matic transmission plants and had stepped up attention to workmanship and design.

"There's no question that we had a problem," Smith said. "But with the new transmissions and the improvements we made in current transmissions, the problem is basically behind us. I'd say we're on the down slope of the curve."

That's all fine and well for new car buyers, but what about the millions of GM car owners who have trouble-prone transmissions in existing GM cars, which often provide less than 100,000 miles of service before failure?

The answer is that most likely you qualify for potentially large monetary compensation under an arbitration program that GM instituted with the Better Business Bureau. But reports from GM car owners who have successfully won awards indicate you have to be dogged in your efforts against GM.

The specific GM transmission in your Corvette, a turbo Hydra-matic 400, is a good example of one type of defective transmission that some GM owners have to deal with. You probably have two specific problems.

Not Random

First, the ground-up gear was not a random event. The original-equipment "output ring gear" for first gear in the transmissions was made of a soft alloy that did not hold up well.

GM introduced a new output ring gear with hardened metal during 1985 and recalled all the old gears. The new gears carry identification markings that distinguish them from the old gears. If you got the new gear, you shouldn't have further problems.

Second, the lugging problem may be attributable to several factors. The transmission may be shifting to a higher gear at too low a speed. If that's the case, then an adjustment is needed in the "governor," which measures road speed and tells the transmission when to shift.

But more likely, the problem is with the computerized lock-up control. Transmissions typically transfer power through fluid couplings. But your transmission has a device that creates a mechanical linkage from the engine to the drive shaft.

This lockup occurs at certain speeds and with certain road conditions. It is all governed by a memory chip in a computer in the engine compartment. That chip, called a Programmable Read-Only Memory, is calibrated to expected road conditions in different parts of the United States. One transmission expert claims that there are more than two dozen PROMs for your transmission.

Your lugging problem may well result from a disparity between what the memory chip in your car expects in your geographic area and your actual usage. If that's your problem, only a top-notch transmission expert is going to be able to help.

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