Dim Light May Be Warning to Replace the Alternator

Question: I have a 1979 Buick Regal with very low mileage--30,000 miles. A couple of months ago, the generator light would not go completely out. It stayed on with a very dim light at any speed. The battery still seems to have enough charge to start the car and keep the lights bright for night driving. How long would this condition have to continue before a problem develops?--G.W.K.

Answer: The alternator and related parts of the charging system are probably putting out a positive charge, but it may not be adequate in the long run or during periods of heavy electrical usage.

The charging system is rated at about 65 to 70 amps, but with the dim light showing on the indicator, it might be putting out only about 45 amps. In some cases, that might be adequate, but not under a heavy load.

If you use the rear window defroster, the heater blower, the headlights and other accessories, you may drain the battery. If the drain is severe enough, the next time you try to start the car you won’t have enough charge.

The problem is most likely a failure in the alternator’s rectifier or diodes, which are supposed to prevent current from flowing in the wrong direction. The dim light that you see is an indication of that problem, though it could also be other parts, including the voltage regulator.

It is still possible to replace only those parts by taking apart the alternator, but the labor charge at most garages to fix the alternator would be higher than to simply replace it.

Q: I sometimes experience trouble shifting the manual transmission of my Nissan Sentra into reverse. I have to try a couple of times, and sometimes I really have to force it into gear. I don’t hear any gears grinding, and it doesn’t matter whether the engine is hot or cold. What is the problem?--A.R.

A: The reverse gears on almost all manual transmissions do not have synchronizers, which I have discussed in previous columns. They are devices that allow gears to be shifted even while they are in motion.

In the case of reverse gears, the car must be fully stopped and the clutch pedal must be fully depressed to shift. In order for these gears to shift when they are stopped, the teeth come to sharp points. The teeth on most forward gears have flat points.

The reverse gears need the points so that when two gears come together, the teeth can smoothly mesh together. If they were not pointed, the gears might get stuck on the flat portion and not mesh.

The problem you describe can result from damage or abuse of the reverse gears that caused their pointed ends to be torn off. For example, if you shift into reverse while the car is in forward motion, you can shear off the points.

There isn’t much you can do about the problem, except to tear open the transmission and replace the gears. You can possibly live with the problem by being careful. You shouldn’t try to force the transmission into reverse, because that will probably damage it even more. If it absolutely will not go into gear, pull forward a few inches and then try to get into reverse. By moving the car, you may get the flat portions to align correctly.

Q: I have a 1982 Honda Accord with a little over 32,000 miles. The problem is that every few days when I start the car in the morning, it will hit on only three cylinders. After driving a few miles, it clears up. What’s causing this?--J.P.

A: One of the spark plugs is probably misfiring. Instead of the spark jumping from the tip of the plug to the side electrode, the spark jumps out to the base of the plug. Sometimes, this condition is caused by a crack in the ceramic insulation.

Even without a crack, once a spark plug misfires, it will do it again. It is more common when a car is driven only on short trips and the engine doesn’t get a chance to fully warm up. If you have put on only 32,000 miles in six years, your car probably never fully warms up. A simple tuneup and new plugs should clear up the problem.

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.