What Is a Distributor in a Car?

Dustin Hawley | Feb 14, 2021

A distributor is an essential part of any mechanical ignition. They’ve been in use since 1910, on millions upon millions of vehicles.

classic car distributor.jpg

If you’re younger than a certain age, there’s a high likelihood that you have never seen a distributor because mechanical ignitions have fallen out of favor since the late 1990s. Most modern vehicles today use a computerized engine control unit (ECU), which controls either a capacitive or inductive electronic ignition.

That being said, there is still good reason to understand what a car distributor is and how it works, not the least of which is that they’re an essential component of any classic car. The following is a short guide to help educate you on what exactly a distributor is.

How Does a Distributor Work?

A distributor is an engine component that supplies power to each of the vehicle’s spark plugs. The basic concept is simple and straightforward; the ignition coil delivers power to the distributor cap, sending it to each individual spark plug via the spark plug wires.

The complicating factor is that the spark plugs need to fire in the correct sequence and timing in order to operate effectively. This is where a distributor comes into play, as it does this mechanically. A gear is located at the bottom of the distributor and then connected to an additional gear on your vehicle’s camshaft.

As the camshaft turns, the internal distributor components turn accordingly.. Because the distributor speeds up and slows down with the engine, it should remain set once the timing has been calibrated. Older vehicles often allowed you to adjust the base timing, while later models typically had a fixed timing.

As the voltage from the ignition coil enters the distributor cap, it is transferred to a rotor located in the center of the distributor housing. This rotor is the part that turns along with the camshaft, keeping time with the motor. The spinning rotor makes contact with terminals on the perimeter of the housing, and these terminals connect to the individual spark plugs. Ensuring the correct firing sequence requires that the spark plug wires be connected to the distributor in the right order.

Some types of distributors also include additional components. Most newer distributors contain pickup coils that actuate when the rotor contacts them, which communicates the engine firing to the ignition control module. In other models, the control module is inside the distributor. This is one reason it’s essential to use the correct distributor for your vehicle.

Some cars also use the distributor to drive the engine oil pump since the distributor is already timed to the motor.

Symptoms of a Bad Distributor

Now that we know how a distributor works, it’s time to discuss what happens when it doesn’t work as intended. There are several possible symptoms of a bad distributor, but these are some of the most common:

  • Your car doesn’t start. This happens when there’s no connection between the ignition coil and the spark plugs. Usually, the cause is a loose distributor cap, although ignition failure can also occur if the cylinders are out of sequence or one or more wires have failed.
  • Your engine is rattling, tapping, or clicking. This noise is the result of one or more cylinders failing to fire. The engine is still working, but it’s not working at optimal efficiency. Misfires will also put added stress on your camshaft, resulting in premature wear and tear.
  • Your Check Engine light is on. The dreaded Check Engine light can be triggered by just about any vehicle component. You can use an OBD or OBDII scanner to read the codes and see if the error displayed has anything to do with the distributor.
  • You failed your emissions inspection. A misfiring engine is far less than optimally efficient and can cause you to fail your state emissions test.

Common Causes & Solutions to Distributor Failure

  • The most common cause of distributor failure is damage or loosening of the distributor cap. The cap is a relatively flimsy piece of hardware and is subject to a lot of stress due to heat and engine vibration. Thankfully, caps are relatively cheap and easy to replace when they’re damaged. Another related cause is carbon buildup on the distributor cap’s terminals. You can easily clean these terminals with a wire brush.

    When you do have to replace your distributor cap, make sure to reconnect the spark plug wires in the right sequence. Most caps will have a marking at the number one cylinder wire. Take note of this wire and mark all the others in the same sequence as you remove them.

    When you attach your new distributor cap, attach the number one spark plug wire to the number one connection. Reconnect the others in the same sequence they were removed, and everything should function properly.
  • The distributor itself can also be damaged by water infiltration. Suppose your vehicle runs through a deep puddle or flooded road. In that case, water may enter the distributor housing, causing the electrical current to short out and redirect the current to the vehicle frame - likely leaving the engine unable to turn over.

    To fix a flooded distributor, you’ll need to dry it out thoroughly. Always start by removing the cap and rotor, then wipe everything down with a shop towel, or you use compressed air to get the job done faster. WD-40 is another quick and easy way to force the water out of the distributor. Some distributors have a gasket between the cap and the main housing to prevent water from getting in. Keep in mind that this is part of the distributor, not part of the distributor cap. So when you change your distributor, make sure to hold on to the gasket and reuse it.
  • The distributor can also fail due to contamination by dirt, oil, and other materials. If your distributor is dirty, it can be cleaned easily with brake cleaner, electronics cleaner, or another petroleum-based solvent.

Summary

A distributor is the part of your ignition that sends electricity to the spark plugs and causes the cylinders to fire. It’s always unfortunate when you run into mechanical issues with your vehicle. But luckily, if you experience issues with a distributor, it’s one of the more manageable automotive parts to replace. If you want to learn more about your vehicle, read more of our helpful guides!

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