What Are the Main Causes of Clutch Shudder?
4 Answers
Clutch shudder is mainly caused by: 1. Broken friction disc lining; 2. Excessive elasticity of the clutch compression spring, leading to clutch vibration. The clutch is a device that transmits the engine's power to the axle in an on-off manner, installed between the engine and the transmission, directly connected to the engine in the vehicle's powertrain assembly. The functions of the clutch are: 1. Ensuring smooth vehicle starting; 2. Achieving smooth gear shifting. The maintenance methods for clutch usage include: 1. Cleaning thoroughly before installation to remove anti-rust grease and debris; 2. Adding lubricating oil between friction discs when operating a wet electromagnetic clutch; 3. Ensuring axial fixation during coaxial installation to prevent axial movement between the driving and driven parts; 4. Maintaining coaxiality within 0.1mm between the driving and driven parts' shafts during separate shaft installation.
As a veteran driver with thirty years of experience, I've seen plenty of clutch shudder cases. The most common cause is a warped pressure plate. The pressure plate is supposed to evenly press against the clutch disc, but prolonged heat exposure or improper installation can cause deformation, leading to uneven force distribution and shudder during engagement. Another major factor is a worn or oil-contaminated clutch disc that slips. Even an unevenly worn flywheel can cause rough engagement. Sometimes, even deteriorated engine mount bushings can induce secondary vibrations. My advice is to pay attention to shift timing during normal driving—avoid prolonged clutch slipping in semi-engaged states, as it accelerates overheating and deformation. If shudder occurs, get it checked promptly at a repair shop to prevent costly transmission system damage.
Repair shops frequently encounter cases of clutch shudder. The core issue lies in the flatness deviation of the clutch pressure plate, which may be caused by manufacturing tolerances, deformation due to prolonged high temperatures, or even fracture of the diaphragm spring. If the friction disc surface is contaminated with oil or has burn spots, varying local friction coefficients can cause impact-induced vibrations. When the flywheel working surface wear exceeds 0.2mm, machining is required. Many overlook that a stuck release bearing can also interfere with the pressure plate's even release. When shudder occurs, it's recommended to first check if the engine mount rubber pads have collapsed - this contributing factor is often neglected. During diagnosis, we use a micrometer to measure pressure plate flatness; replacement of the assembly is needed if deviation exceeds 0.1mm.
Over the years of playing with modified cars, I've encountered many clutch failures. Shaking is usually caused by uneven contact surfaces of the pressure plate or flywheel, especially in modified cars where the pressure plate bears greater force and is prone to deformation. If the clutch disc wears unevenly or develops hard spots, the engagement moment feels like walking on cobblestones. If you notice shaking accompanied by a burnt smell, it's likely the friction disc is burnt. Operating habits like excessively long semi-engagement periods are particularly damaging to the clutch, such as frequently riding the clutch to control speed during hill starts. I make it a habit to regularly check the clutch pedal free play, keeping it between 15 to 20 mm is ideal. When replacing the clutch three-piece set, it's best to perform a flywheel surface inspection, and for modified cars, upgrading to a reinforced pressure plate is recommended.
