Valve May Unlock Braking Problem
Question: I have a 1981 AMC Spirit. When I brake suddenly, the back end tends to swing around. Once, while braking for a sudden slowdown on the freeway, I actually spun over. I’ve had the brakes checked, and there doesn’t seem to be a problem. Can you suggest something?--R.C.
Answer: You certainly have a problem, regardless of what you have been told. AMC has recognized that some Spirits have problems, although so far it doesn’t appear serious enough to warrant a national recall.
Your rear brakes possibly may be locking up before your front brakes, which will cause a loss of control. If your rear brakes lock up, the car will have a tendency to fishtail.
Your Spirit has front disc brakes and rear drum brakes. Such setups are common in many cars, but they require a somewhat more complicated hydraulic system than cars with similar brakes at all four wheels.
When you depress your brake pedal, hydraulic fluid is pumped to all four brakes, but the pressure required to activate the two front disc brakes is not the same as that required by the two rear drum brakes. So, a proportioning valve is installed in the system to allocate a different amount of hydraulic pressure to the front and rear.
AMC has developed several different solutions to the problem and has issued technical letters and service bulletins to its dealerships on the matter. One solution is to install a different proportioning valve to decrease the hydraulic pressure sent to the rear brakes.
You should take your Spirit to a dealership for this type of service. It is possible, depending on the mileage and the judgment of the individual dealer, that the work will be performed at no cost. You should raise that possibility with the dealership’s service manager when you take the car in.
Q: I own a 1979 Oldsmobile Toronado with a 350-cubic-inch, four-barrel carburetor engine. While driving and coming to a stop at an intersection, the engine acts as if it is dropping one cylinder and wants to quit running. At higher speeds, it is normal. I have put in new spark plugs, wires, distributor cap, rotor and ignition modules. What could be the cause?--W.J.W.
A: It’s likely that your engine is not “dropping” a cylinder when you stop, but missing all the time, and you simply don’t notice it at higher speeds.
One possible source of your problem is a vacuum leak, which can cause a very rough idle that will disappear at high speeds.
The 1979 Toronado has a vacuum-operated ignition advancing system. In 1980, Oldsmobile began using an electronic advance system. A leak in this system could be one source of your trouble.
Q: How many miles should a car be driven before it becomes advisable to replace a coil?--P.S.
A: A coil is one ignition part that is almost never routinely replaced. The coil is a transformer that converts your car’s 12-volt electrical energy to 20,000 volts, which is sent to the spark plugs.
The coil consists of 200 windings of primary wire and about 22,000 windings of secondary wire, all wound around an iron core.
Coils are one of the most durable parts of the ignition system and are capable of lasting more than 100,000 miles. Usually, they are replaced when they fail. You’ll know when that happens because your car won’t start.
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.
