Hi Jim, my brother has 5 of these IH/CIH 54/74/84/95/32XX series tractors. Many years ago the 454 was used on the manure spreader and when you came to the end of the field and slowed the engine RPM down but the beaters on the manure spreader wanted to continue running at the same speed we would hear a clicking noise from the clutch housing area. Other PTO implements had an overrunning clutch and you would never hear anything. When we had to replace the clutch on the 454 there was only about 1/16" inch tooth left on the pressure plate splines. The PTO input shaft was still good and the clicking noise disappeared when using the manure spreader. We have changed the clutch on the 684 twice and the 495 once. The 495 had no spline ware as the PTO is not used that much. The 684 had some spline wear but not significant. PS, maybe my description of the sound is not accurate but I can appreciate if the 454 clutch hadn't been replaced eventually the spline teeth would have stripped and the noise would have changed to a grinding noise.