When your Plymouth clutch begins to show signs of slipping, blame it on the physics of heat and friction. No matter how well-engineered your Plymouth clutch is, the components cannot endure the pressures of heat and friction indefinitely. 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 are key to making a long-lasting clutch, since the constant heat and friction that Mercury clutch components endure will eventually wear down on them. That friction material is pretty similar in composition to the friction material on the pads of a disc brake, or the shoes of a drum brake. When most or all of the friction material wears away, you will notice a slipping clutch that will eventually stop transmitting any power from the engine to the wheels. Improvements in the engineering and design of Plymouth clutches 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.