The 'six-shooter' drum, concurrent with the steel fork sliders, was on the first two years of 650 Yamaha, then called the XS1 (and then XS1b in it's second year, 1971) It has a poor reputation, not for falling apart, like some of the Suzuki drums from the period, but for just being a not-very well-designed brake to begin with; the conecting rod for the second cam operates in compression rather than extension, and the the brake-cam arms have two different operating ratios, meaning they will never be working equally. Maybe Yamaha was also thinking, "it's not a motorcycle baby; it's a chopper" because it does at least look good, with it's cooling scoops and backside vents and so forth. A guy who had one in the day told me that when you grabbed a handful of front brake, the only thing that happened was a slight grinding noise from the front end, without any appreciable deceleration...
