I was taking my elderly mother to visit her cousin in my recently acquired '68 GTO convertible and in the course of conversation, she asked me what "synchromesh" meant. I replied that it meant you could put the transmission into any gear without double clutching or matching the engine RPMs. And then proceeded to demonstrate. We were coming down out of a canyon and were going about 60. I pushed in the clutch and downshifted the transmission into third, then second, and all was fine. As I attempted to shift from second down to first, there was some resistance, but I persevered, and when it finally went into gear, I was rewarded with a loud bang from under the hood. The clutch would no longer engage.