That annoying 'chatter' or grinding noise you hear when you shift your GMC clutch is a sign that it might be failing. Your clutch, after all, undergoes tremendous pressure and heat stress every day, and eventually the three main parts of the GMC clutch - the flywheel, disc and pressure plate-- will begin to wear down the friction surfaces of these parts until the surface is too thin to transmit enough torque to move the car normally. Some of the new technology improvements in clutches can be seen in the friction materials used to build the clutch components, and updates in the pressure plate, including centrifugally assisted diaphragms. Some of the new extremely strong units are made from steel or high-grade aluminum alloy. Those improvements have made it possible for most clutches to last more than 80,000 miles, compared to the norm of 50,000 to 60,000 miles that was seen in cars through the 1970s. But the same concept applies to clutches since they were invented: The GMC clutch works to help the engine's spinning parts engage - or disengage - with the turning wheels. The clutch acts to join or disconnect the transmission from the car's wheels, and is activated by the pressure of your foot on the pedal. That pressure pushes the pressure plate against the disc, which then presses against the flywheel.