What are the symptoms of a broken engine flywheel?

[SanDiana]

Engine flywheel failure symptoms include: crankshaft fatigue, longitudinal cracks in the flywheel housing, etc. The flywheel is a disc-shaped component with significant rotational inertia, functioning as an energy storage device. For four-stroke engines, only one power stroke occurs every four piston strokes—meaning only the power stroke generates work, while the exhaust, intake, and compression strokes consume energy. This results in periodic torque fluctuations from the crankshaft and unstable crankshaft speed. To mitigate this, a flywheel is installed at the rear end of the crankshaft. Positioned at the crankshaft's power output end (connected to the transmission and working equipment), the flywheel primarily stores energy and inertia outside the engine's power stroke. In four-stroke engines, the energy for intake, compression, and exhaust strokes is supplied by the flywheel's stored energy.

[LaEvangeline]

Last time, my friend's old Passat had a flywheel issue. When starting the car, there was an extremely harsh metal grinding noise from the engine bay, like the screeching sound of scraping a plate with a piece of iron. Pressing the accelerator caused severe body vibrations, especially noticeable when climbing hills at low speeds—you could feel the clutch pedal shaking along. The most obvious symptom was when idling at a red light in neutral; the engine RPM would fluctuate up and down on its own, as if it couldn't catch its breath. Once, during a long drive, we noticed the car struggled to accelerate on the highway—pressing the gas pedal hard didn’t translate to speed, and the tachometer needle swung wildly. The mechanic said the damping springs in the dual-mass flywheel were broken, and failing to replace them promptly could wreck the transmission gears. In the end, it cost nearly five thousand yuan to fix.

[AylaLynn]

Having driven manual transmission for ten years, I once encountered a flywheel failure. The most typical symptom was loud banging noises from the entire chassis when engaging the clutch. Cold starts were relatively normal, but after warming up, the car would inevitably shudder during takeoff, resembling rhythmic vibrations like going over speed bumps. The moment of releasing the clutch after shifting gears was particularly noticeable, feeling as if the engine compartment was pounding against the frame. A mechanic once taught me a makeshift diagnostic method: pull the handbrake, engage first gear, and slowly release the clutch. If the RPM doesn't drop but the car body shakes violently, it's almost certainly due to broken flywheel engagement teeth. This kind of failure accelerates wear on the transmission mount bushings, and on one occasion, it even cracked my AC piping due to the vibrations.

[McNevaeh]

Last time I helped my neighbor check his Wuling Hongguang, I discovered a flywheel issue. The starter motor was turning with great difficulty, clicking seven or eight times before the engine fired up. At idle, there was a regular buzzing sound coming from the driver's seat floor, making it feel like stepping on a massage chair. When driving, acceleration was weak, and the tachometer would suddenly drop by 500 RPM when climbing hills in third gear. The most dangerous part was reversing into parking spaces—the car would lurch forward and backward uncontrollably the moment the clutch was released. The repair shop found that the flywheel surface was warped, with half-millimeter-deep grooves worn around the circumference.

[StDavid]

My best friend's automatic Honda Fit had a flywheel failure last year, causing a constant low humming noise inside the cabin. When exceeding 60 km/h, there was low-frequency vibration similar to being on an airplane. During traffic jams, a rattling 'clunk-clunk' sound came from the rear when braking in D gear, which disappeared when shifted to N gear. During sudden acceleration, the ESP light on the dashboard flashed erratically, and the acceleration process became jerky. The dealership inspection revealed broken damping springs inside the dual-mass flywheel, with metal fragments even scratching marks on the transmission oil pan.

[MaddoxLee]

The worst nightmare for car modders is flywheel failure. During a track day, my RWD car suddenly had clutch slippage at launch - revs soared to 5000rpm but speed wouldn't increase. Between gear shifts, metallic clanking sounds came from the engine bay, and weird gurgling noises occurred during aggressive downshifting. Teardown revealed the locating pins on my lightweight racing flywheel had sheared, causing the entire flywheel to wobble on the crankshaft flange and grind grooves into the engine block. This damage disrupts crankshaft balance and in severe cases can score cylinder liners.