Baffling ’Bird ’box
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Well, firstly, if the bike moves forward kicking over with the clutch withdrawn, it’s in gear, not neutral.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