WHERE AUTO DEFECTS COME FROM

THE U.S. prides itself on having the world's most efficient industry. If that is the case, why have auto manufacturers, long regarded as star performers, lately been recalling cars at a faster rate than they have been building them? Last week General Motors called back 1,100,000 vehicles--1965 and 1966 Pontiac cars and late-model Chevrolet and G.M.C. trucks, buses and highway tractors--because of possible defects in the braking systems. Only three weeks earlier, G.M. had recalled a record 4,900,000 vehicles, including 2,500,000 Chevrolets built between 1965 and 1968. Although less than 5% of all autos involved usually turn out to be defective, such recalls underscore the fact that Detroit's quality control is not all that it might be. Says G.M. Chairman James M. Roche: "We'd be the first to admit that a better job can be done."

Car buyers, especially those who may spend anywhere from $2,000 to $8,000 for a lemon, would certainly agree. Yet the same buyers make improved quality control difficult by insisting on speed and styling at the lowest possible price. In the hot competition for customers, the need to squeeze every last dollar out of production prompts automakers to cut costs in designing their cars. An innovation that endangered 2,500,000 of the cars in last month's G.M. recall was a cam used to regulate the engine's idling speed. It was designed in plastic, which enabled production engineers to hold down tooling costs. The trouble was that the cam broke off on some vehicles and dropped into the throttle linkage, jamming the accelerator. The company is now substituting a stronger, metal-reinforced cam.

Less Pride. In G.M.'s latest recall, another engineering error involved air brake valve hoses that were placed close to the left front tires on certain highway tractors. The hoses at times rubbed against the tires and wore through, causing brake failure. Chrysler last year mailed new gasoline tank caps to 25,000 of its customers to replace a faulty one that posed a safety peril. The old cap had a rubber seal that, because it tended to swell up and cover the cap's air hole, could have caused the gas tank to collapse.

Whether problems are created on the drawing board or crop up during manufacture, human error is almost always involved. Auto executives privately complain that today's assembly-line workers, who earn $5.50 an hour in wages and fringe benefits, tend to take less pride in their jobs than their elders. American Motors had to recall 750 cars over the past year because workers carelessly installed the wrong alternators, which did not generate enough current to keep the batteries fully charged under heavy loads. To overcome lax workmanship on the production line, G.M.'s Buick Division not long ago outfitted torque wrenches with horns that sound off whenever workers fail to fasten nuts and bolts tightly enough. Quality control is becoming an increasingly big headache on Mondays and Fridays, when high absenteeism forces management to rely heavily on backup men.

A more fundamental cause of defects than engineering or labor failures is the sheer complexity of today's cars. The average auto has as many as 15,000 parts, 1,400 of which are subject to friction because they move. The proliferation of model changeovers and optional equipment increases the many chances of error. To ferret out flaws, Detroit has put increasing reliance on technological innovations, many of them borrowed from the aerospace industry.

Automakers now use sound waves to detect defects in axle shafts, connecting rods and many other parts. Ford uses computers to program simulated road conditions for testing new wrinkles before they are incorporated into its new autos.

Bumpy Roads. Auto recalls are scarcely new. Back in 1916, Buick called back touring cars and roadsters after their gas tanks, attached to the body by straps, showed a disturbing tendency to fall off on bumpy roads. From 1960 until Auto Critic Ralph Nader's safety crusade led to the federal Highway Safety Act of 1966, Detroit called back 8,700,000 cars. In the 30 months since, however, 11,400,000 vehicles have been called back.

"It is virtually impossible to guarantee that no defective vehicle will ever reach consumers," says William Haddon Jr., former director of the National Highway Safety Bureau. The ways that autos can go wrong are varied and subtle and, no matter how hard the auto companies work to root out potential defects, there will probably always be some bugs. Nonetheless, the auto companies are more aware than ever that added vigilance is needed to eliminate such defects. In a sense, the growing number and size of recalls is itself a sign of the industry's increased vigilance.

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