Campag braze-on front mech to shift 61/46?

[chriscross1966]

For reasons I won't bore you with I need to get a mech that will reliably shift a set of TA Specialities 61/46 rings. Becasue the rest of the bike is Campag it needs to be too (they're on an old 135BCD Chorus crank that I'm assuming is 8-speed, but I guess could be 9 (but it just has a shield logo adn I thought the 9-speed had writing) .... I'm running it 7-speed so if I have to shim it I will, but does anyone know if I'll have a problem with just fitting any old Campag front mech that looks pretty (so basically shield logo and no writing), I'd prefer to avoid the triples and LX/Rallye front mechs, and I'm guessing the off-road ones will be for smaller rings

 

[fossyant]

Good luck finding something.

 

[chriscross1966]

They're old rings and 135bcd can only really be for Campag cranks, so I'm hopeful

 

[Ajax Bay]

does anyone know if I'll have a problem with just fitting any old Campag front mech that looks pretty

I've just measured my 80s Campagnolo Record FD and SR Apex chainset (54/40 fitted).
The critical dimension is the differential between the large and small ring and the vertical drop the FD cage allows. I have 54/40 and the differential between the rings is ~30mm. The cage allows this. Your 61/46 differential will be about the same. The curvature of the (road obv) FD will not align with the 61t ring, obviously, but the drop to its back will be the same so I think it will work. I would expect changing up will need more care but changing down will operate normally (care with limit screws). HTH

 

[chriscross1966]

I think I'm going to try with Victory mechs on it, they're somewhat crude, but they do have the advantage of looking nice and also have a reputation for shifting when you tell them to..... not quietly, and with significant recoil through the controls, but they WILL shift....

 

[rogerzilla]

Is the slot in the braze-on long enough to clear a 61T?

 

[Ajax Bay]

Each extra tooth on a chainring means a change (increase) in radius (and therefore FR cage height) of almost exactly 2mm (12.7mm /2Pi).

 

[chriscross1966]

Is the slot in the braze-on long enough to clear a 61T?

I've got a clamp on braze-on if you see what I mean, so that won't be an issue