Baf­fling ’Bird ’box

Classic Bike (UK) - - Classic Workshop -

Eddy Ham­ley is hav­ing trou­ble with his ‘swamp bike’, a ’58 Tri­umph Thun­der­bird in ‘un­re­stored’ con­di­tion. He says: “The gear­box (like the owner) was al­ways re­luc­tant to change, but now the gear pedal won’t move at all.” But if he pulls the clutch lever, the pedal moves slightly; while turn­ing the kick­start with the clutch held in, the bike creeps for­ward. “If I try to roll the bike it feels like it’s in gear, but if I re­ally force the gear pedal down, I can move the bike for­ward. Do you think I should strip the clutch or look into the gear case for the prob­lem?” he asks.

Well, firstly, if the bike moves for­ward kick­ing over with the clutch with­drawn, it’s in gear, not neu­tral. Sec­ond, since it’s a 1958 bike it prob­a­bly has a ‘Slick­shift’ gear­box, iden­ti­fied by hav­ing a chrome cover, se­cured by two screws, just be­hind the gear pedal. It was a short-lived (and in­ac­cu­rately named) ’box; a cam on the gear­lever mech­a­nism au­to­mat­i­cally lifted the clutch – a bit like a Honda step-thru. It was sup­posed to of­fer a backup to get around a bro­ken clutch ca­ble, but in prac­tice the ac­tion was so fierce it was more likely to cause an ac­ci­dent, so most were dis­con­nected. Eddy’s seems to be still work­ing, which ex­plains why the gear pedal moves slightly with the clutch and why forc­ing the pedal down dis­en­gages it enough to roll the bike in gear.

It sounds like it’s just stuck in gear, sug­gest­ing a fail­ure in the gear se­lec­tor mech­a­nism. I’d guess one of the springloaded pawls that en­gages with the quad­rant has turned or jumped out of its hous­ing, al­low­ing the pedal to move into first but not come back again into neu­tral. So Eddy needs to start by re­mov­ing the gear­box cover not the pri­mary chain case.

Pawls on gear se­lec­tor can be­come dis­lodged

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