Auto Care

Flexplate – What does it do ? – What happens when it fails ?

Flexplate - What Does It Do ? - What Happens When It FailsFlexplate - What Does It Do ? - What Happens When It Fails
Flexplate – What Does It Do ? – What Happens When It Fails

In vehicles with automatic transmissions, a metal disc called a flexplate, connects the crankshaft to the torque converter.

So, a flexplate, as the name implies, serves as a flex-shock device; between the torque converter and the engine crankshaft.

A flexplate consists of a steel circular disk with perforated holes. And, is also balanced to improve, smooth running. Consequently, flexing allows it to respond to small differences of alignment, between the engine and the transmission.

Flexplates actually consist of two parts. The flexplate and the ring gear, fitted to the outside of it.

Ring GearRing Gear
Ring Gear

The starter motor, engages this starter ring gear to start the engine. There may be times that you have to remove it. But, if you have to remove the flexplate, it must go back on the same way. Because, balancing is very important.

What Happens When It Fails

The bolts are torqued in a crisscross pattern, according to the manufacturer’s specifications. The torque converter used with an automatic transmission, acts like a flywheel, smoothing out engine pulses.

Flexplate Cracking On Various Engine Applications Is Common

The cracking on these flexplates can be seen, either around the crankshaft or torque converter bolt hole patterns.

Flexplate Cracking Around Bolt HolesFlexplate Cracking Around Bolt Holes
Flexplate Cracking Around Bolt Holes

What Can Cause, A Cracked Flexplate:

  • Out of balance engine or torque converter.
  • Bad starter drive, can cause teeth or ring gear to wear rapidly or break off.
  • Teeth can also break, when engine is running and starter is engaged.
  • Failure to torque the bolts, to proper specifications and in proper sequence.
  • Failure to use starter shims, where required.
  • Poor quality parts.
  • Missing Dowel pins.

A loose bolt on a flexplate or a crack between it’s bolt holes can result in a; knocking or rattling sound. The sound is very similar to a bad connecting rod and is often, misdiagnosed.

The flexplate can become cracked over time. As a result, this can cause the it, to wobble. So, you might notice rhythmic clunking or grinding noises, while the engine is running.

Visible CracksVisible Cracks
Visible Cracks

A misaligned flex plate, can also keep the engine from running smoothly. So, if you suspect you have a flexplate problem, there are a couple ways to investigate further.

So, if you listen to the transmission bell housing with a stethoscope, while the engine is idling; any sounds coming from inside the bellhousing indicate, flexplate problems. Some bell housings have an, inspection port. If so, remove the inspection port and shine a shop light on the flexplate for a, visual inspection.

Starting Problems

A warped flexplate won’t engage properly with the starter motor. So, when you are starting your engine listen for, rhythmic bogging down of the engine, during starting. Consequently, the teeth of the ring gear, can become damaged over time, causing a grinding sound.

Damaged Ring Gear TeethDamaged Ring Gear Teeth
Damaged Ring Gear Teeth

Ring gear problems can damage the starter motor as well. So, if you find you have to replace your flex plate, you might want to check your starter as well.

Damaged Flexplate Causing NoiseDamaged Flexplate Causing Noise
Damaged Flexplate Causing Noise

A cracked flex plate is almost always, a sign of other problems. So, if not properly diagnosed, it will occur again and often damage to the transmission may follow. The same things that caused the flexplate to crack, can also cause transmission problems. In addition, damaged and leaking front seals; and front transmission pumps are common symptoms.


So, a engine making noise when starting, often indicates either a; starter failure or broken teeth on your transmission flex plate. Also, some cars require several hours to replace the starter and hundreds of dollars, for a replacement part.

However, if your car needs a new flex plate, it’s a much bigger issue. Because, the transmission must come out, to replace the flex plate. For instance, it’s $1,500 and up, to replace a flex plate, in most vehicles.

Thank You !

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