Friction damper, 1951 MV Agusta 150 Sport Racer.
It's interesting how this bike fits into the evolutionary chronology of shock absorber design. The red and silver tube looks like an enclosed tube shock or shock/spring unit, but all it contains is a coil spring. The polished silver scissors linkage to its right is the shock, or more properly the friction damper. The two arms interlock under the big diamond-shape wing nut and six-pointed hand adjuster, interleaved with a pair of oiled leather washers to tame the spring's action. Want more damping? Crank down on the adjuster, increasing pressure on the leather washers to create more friction and resistance.
Articulated friction dampers of this type were de rigeur for early automobiles and motorcycles through the 1930s, before falling out of favor and being replaced by hydraulic lever shocks in the post-WWII era, which were in turn displaced in the 1950s and 1960s by the telescopic hydraulic units you see today.
I like how the evolutionary pathway wasn't a straight-up leap from articulated friction damper to tube shock. The technology progression had to first morph the lever arm friction design into a hydraulic version with a lever arm, and then adapt the hydraulics into a telescopic design—a form factor presaged by the enclosed coil spring you see mounted here, right next to the lever shock. (In fact, the following year's MV Agusta dispensed with the friction damper, replacing it with the now-familiar coaxial coil spring and tube shock.) With thanks to Moto Talbott's curator, Bobby Weindorf, for being fabulously informative and accommodating, and especially for the tidbit about the 1952 MV Agusta.
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