A Quick Guide to Flex Plates

In a manual car, the flywheel transmits and regulates power from the engine that goes to the manual transmission. But what is its automatic equivalent?

The flex plate is the closest thing to a flywheel in an automatic car. However, it’s not a one-for-one equivalent.

What Is a Flex Plate?

Also spelled as flexplate, the flex plate serves as the drive plate of an automatic transmission. This metal disk is bolted to the crankshaft. Furthermore, the torque converter is mounted on the flex plate. The flex plate’s position and physical connection to the engine and transmission enable the part to bridge the two automotive systems together.

The flex plate gets its name from how its thin shape flexes in response to the force applied by the crankshaft. Its flexibility can compensate for gear shifts, erratic power output, and minor misalignments between the engine and transmission.

Flex plates consist of two parts, the plate itself and the ring gear. The latter is a toothed gear that runs around the flex plate’s circumference. When you start your car, the ring gear engages with the starter motor, allowing the engine to crank up.

In some vehicle models, the flex plate also incorporates the pickup ring of the crankshaft position sensor. Also known as the tone ring, the pickup ring is a notched ring that relays firing commands to the powertrain control module (PCM). If the pickup ring develops an issue, you must replace the flex plate that incorporates the crankshaft position sensor.

In most vehicles, the flex plate is made of stamped steel. High-performance cars feature machined billets. Race cars use a two-piece billet, while dragsters have a one-piece billet.

What Does a Flex Plate Do?

The flex plate captures the energy created by the engine. It stores the collected energy in its large mass by spinning at an even and smooth speed. At the right moment, the plate releases the stored energy to the transmission. The transmission then splits the energy between the drive wheels to propel your vehicle.

If the flex plate has a tone ring, it helps the crankshaft position sensor determine the position and RPM of the crank. The PCM uses the readings from the crankshaft position sensor to set the right time for processes like ignition and fuel injection.

Common Flex Plate Issues

The flex plate is a tough part. It must withstand the significant forces imparted by engine power that the plate stores and transmits to the torque converter.

However, the part’s namesake flexibility can only take it so far. Cracks can form in the flex plate. If you continue driving without replacing the damaged plate, this part can fail.

Aside from the flex plate, the bolts securing the plate to the crankshaft can loosen up or break apart. Loose and damaged flex plate bolts will cause problems of their own. Fortunately, you can tighten loose bolts, although you must also tighten them in the correct sequence.

What Causes Flex Plate Problems?

There are several possible reasons behind flex plate problems. For example, the torque converter or engine might become unbalanced, which affects the plate’s alignment.

Alternatively, the starter motor can wear out or damage the ring gear when the two parts engage during the start-up sequence. If the motor can’t lock with the faulty gear, it might lead to issues like failure to start the engine.

Improperly installed flex plate bolts can also cause problems with the plate. You must apply the correct amount of torque to the bolts. Furthermore, you must tighten the bolts in the manufacturer-specified order.

Bad Flex Plate Symptoms

The flex plate is a vital transmission part. If it develops a problem, it affects the rest of the transmission. It’s a good idea to keep a lookout for the warning signs of a bad flex plate.

Here are some of the most common symptoms of a faulty flex plate:

Whining Noises During Engine Start

You can spot a bad flex plate when you start your car. Listen for a metallic noise when the starter motor engages with a toothed flex plate or the torque converter. That whining sound is a possible symptom that the flex plate has an issue.

Strange Noises During Engine Idle or Shifting Gears

If you leave your car idling in neutral or park, do you hear regular clicking or grinding noises? Or do your ears pick up knocking when you shift into forward or reverse gear?

Strange noises like clicking, grinding, or knocking while driving might indicate a misaligned or warped flex plate. The plate’s side has come into contact with other parts, which isn’t supposed to happen.

The most common cause of a misaligned flex plate is broken or loose bolts.

Vibrations While Driving

A bad flex plate can cause your car to vibrate. The faster you drive, the worse the vibrations get. In some cases, this happens because of a dislodged balancing weight.

Other Symptoms

The following are other possible symptoms of a bad flex plate:

• Engine runs rough
• Engine power loss at higher speeds
• Poor fuel economy
• Starter makes whining noise when starting the engine
• Starter bogs down or turns with difficulty

Usually, a faulty flex plate indicates another issue in the powertrain. It’s recommended to check the transmission for a separate that might have cracked or loosened the flex plate.

Fight Excess Vibration With a New Flex Plate

When cracks form on your flex plate, your vehicle can make grinding or knocking noises when shifting gears. The vehicle can also vibrate as you drive faster. This can be quite concerning since you wouldn’t want a broken flex to cripple your vehicle. If you have a damaged flex plate, you should have it replaced as soon as possible. Good thing you can get you a brand new flex plate with just a few clicks at CarParts.com.

When it’s time to shop for replacement parts, you can trust CarPats.com. We have a wide assortment of replacement parts from leading aftermarket manufacturers. Find the part you need by entering your vehicle’s specifications into our vehicle selector to start browsing compatible flex plates. You’ll also be relieved to know that our parts are affordably priced.

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