Bad Flywheel Symptomsby Richard Rowe
Clutches are complex mechanisms and can fail in any number of ways. The most difficult part about troubleshooting clutch problems is that several different types of failure can manifest similar symptoms. Diagnosis isn't exactly rolling the dice, but it certainly does require careful observation and some understanding of the mechanism.
The most common of clutch problems isn't usually in the flywheel; it's in the clutch assembly itself. All clutches eventually wear out and begin to slip, but that's not the problem. Allowing a clutch to slip excessively will affect your flywheel the same way that riding the brakes will affect your discs and rotors; it'll overheat the metal, weaken, warp and crack it. Even slippage because of oil, grease or water contamination can damage the flywheel. A soft pedal and a delay in engagement after release are the basic signs of slippage.
Clutch drag is the opposite of slippage, a phenomenon that occurs when the clutch fails to release completely. Clutch drag will cause the clutch assembly to remain closer to engine rpm during shifting. This will start out as mild grinding when shifting and may eventually result in a failure to engage first gear when starting. Clutch drag isn't a result of flywheel failure per se, rather, failure of the pilot bearing or bushing in the flywheel or crankshaft assembly will cause the clutch to drag and refuse to fully release.
Because flywheel and clutch assemblies are similar in function to disc brake assemblies, they'll also exhibit similar symptoms after warpage. A certain amount of warpage or "run out" is normal, a result of constant heating and cooling. There's no hard and fast line between the flywheel with an acceptable run out, and one that's just warped; the distinction is in the symptoms. A warped flywheel will cause a steadily worsening pulsation in the brake pedal, accompanied by an intermittent rise and fall in engine rpm in later stages of warping.
Clutch chatter is a common problem, and it could arise from a number of malfunctions in the assembly. Clutch chatter is what happens when the clutch "skips" on the flywheel, rapidly grabbing and releasing instead of engaging smoothly. Clutch chatter can come from burned or glazed clutch disc friction material, a worn pilot bearing or bushing, or damaged or distorted clutch disc. Grooves in the flywheel and missing or damaged flywheel dowel pins can also cause chatter, but flywheel-related symptoms also mimic the symptoms of a bad engine mount.
Dual Mass Flywheel Problems
A dual-mass flywheel is a two-part unit. A smaller-diameter flywheel bolts to the engine and sits inside of a drum-brake-like outer flywheel. The smaller flywheel engages the larger one via a set of springs. This design offers a bit of buffering between the engine and transmission to enhance smoothness during clutch engagement. A failing dual mass flywheel will first rattle when depressing or releasing the clutch, then proceed to exhibit symptoms similar to clutch chatter even after full engagement. This malfunction will typically occur during initial engagement and while shifting through the lower gears.
- "Heavy Duty Drivetrains: System and Component Application"; Charles R. Jones; 1991
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