Increased gear rattle noise may occur when changing to an aftermarket performance clutch and/or flywheel, including ACT’s products. The most common gear rattle noise occurs when a vehicle is idling in neutral after a long drive or on a hot day. It sounds like a light knocking or growling sound. Gear rattle is an audible noise transmitted from the impacts between the transmission gear teeth. A vehicle engine’s torsional vibrations (momentary angular acceleration) pass through a transmission causing the separation and resulting impact of the gear teeth. Gear rattle is not to be confused with clutch chatter or out-of-balance vibrations; both of which are conditions mostly felt and generally, not heard. In general, gear rattle is not harmful to the transmission, but can be an annoyance to the driver. It can become a serious concern if misdiagnosed as a transmission or engine problem. Traditionally, automakers have dampened torsional vibrations by using a clutch disc with a spring-centered design and a heavy flywheel. More recently, however, many have started using a dual-mass flywheel to silence the gear rattle in the transmission. Typically, when a dual-mass flywheel is used, the clutch disc features a solid, or rigid-hub, instead of a spring-centered. When changing from a dual-mass flywheel to a solid flywheel, a spring-centered clutch will help dampen the torsional vibrations and reduce, but not eliminate, gear rattle noise. Other contributors to increased gear noise include: dual-mass flywheel to a single-mass flywheel conversion, a solid or rigid-hub center instead of a spring center, stronger dampening springs in the clutch disc, increased engine performance modifications or a lighter flywheel or clutch assembly. Gear rattle is a commonly accepted trade-off for performance.
Gear rattle noise is not a manufacturer’s defect and ACT will not accept warranty claims because of increases in gear rattle noise.