Question: I took my 1991 Chevrolet S-10 Blazer to a Goodyear shop for service to my anti-lock brakes. They replaced my front disc pads and rotors. Ten days later, my power booster blew and I almost had an accident. I took the car back and they found they had inadvertently installed a rotor for non-anti-lock brakes on the right side. They also insisted that it had nothing to do with my power booster failing. --P.R.
Answer: The installation of an incorrect rotor is a sign of incompetence on the part of the mechanic. But it is unlikely the wrong rotor caused the failure in the power booster, the system that provides the force in power brakes.
Nonetheless, the repair shop should have made some kind of a goodwill gesture to absorb at least part of the cost of the booster repair. At least I give the shop credit for 'fessing up to its mistake.
The installation of the wrong rotor resulted in the anti-lock system being electronically disabled, though it should not have affected normal braking. You are lucky, because slapping the wrong brake part into a car can cause a potentially deadly safety problem.
The correct rotor for an anti-lock system has a small wheel mounted on the vehicle side of the disk, which sends out signals to a nearby sensor. Those signals tell a central computer whether the wheel is locked or turning, thereby allowing the computer to prevent brake lock up. But with no signal coming from the wheel, the computer goes into a fail-safe mode and shuts down the anti-lock system.
Other than the signal system, the rotors for the anti-lock and non-anti-lock systems are the same. You could drive for years with the wrong rotor and have a false sense of security.
What is odd about this problem is that you should have seen a brake caution light on your dashboard indicating a malfunction in the anti-lock system. The mechanic should have caught his mistake, either when he installed the rotor without the anti-lock signal wheel on it or when he road-tested the car.
The power booster failure also should not have caused a total loss of brakes. You should have still had manual braking, though it would have meant the pedal went nearly to the floor. Power boosters can fail totally, often as a result of a leak in the vacuum diaphragm.
A motorist who's dissatisfied over incompetent repairs should notify the corporate headquarters for the repair company and the state Bureau of Automotive Repairs at (800) 952-5210.
* Vartabedian cannot answer mail personally but will respond in this column to questions of general interest. Do not telephone. Write to Your Wheels, 1875 I St. N.W., No. 1100, Washington, DC 20006 or e-mail to Ralph.Vartabedian@latimes.com.