You may have heard a greybeard point knowingly to an old H-D^® and mention something about “the mousetrap”. This curious term describes a neat evolutionary item in Harley-Davidson's technological march. The mousetrap, (in Harley^® vernacular a “clutch booster assembly”) is the ominous looking contraption you can find bolted to the frame under the fuel tank of some Panhead and early Shovelhead motorcycles.

In 1952, when Harley-Davidson began offering foot shifting as an option on motorcycles, actuating the existing clutch by hand presented a few problems. The handshift clutch was originally designed to be operated by a rider's leg, which is a much stronger appendage for an average motorcyclist compared to the average hand. Because of that, the geometry of the linkages was originally developed in a way that was incompatible with hand operation for riders who did not possess superhuman strength by simply placing a lever on the handlebar. Since footshifting was optional for quite a few model years, the mousetrap is the genetic link that married the handshift era to the footshift one, by allowing riders to operate the same clutch using different actuation methods, depending on what motorcycle they ordered.

The mechanism uses a very strong assist spring under its decorative chrome cover, and it snaps quickly “over centre” when actuated. The unit requires occasional adjusting to keep it in good working order. If one is not careful or knowledgeable about how to make the adjustments, the nasty pinched finger that results pretty well explains the nickname!