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front shifting woes - braze-on issue?
In the two years I've had my bike, the front shifting (shimano STI triple),
has never been great. The major problem has been that the front derailer bottoms out against the seat tube before it can push the chain onto the granny. And while I've had success getting it to work, the adjustment is _extremely_ sensitive, such that when I make any sort of drivetrain change, it can be a nightmare to get working properly again. My question is - is this likely an issue with my braze-on? This is a hand-made frame, so could it be that the braze-on is not allowing the proper distance between f.der and seat tube? I've tried two different deailers with the same result. I could go with a wider bottom bracket, but that would mess up my chainline. Is there a 'standard' for the seat tube to derailer (say, the mounting bolt) distance? I'm seriously considering removing the braze-on so that I can use a clamp-on front derailer. I'm sure an hour or so with my hacksaw and dremel would take care of it nicely, albiet leaving a nasty scar on my beautiful frame. Any tips? I've considered going to friction or Campy front shifting, but if the derailer can't move in far enough, those solutions won't help. Thanks, Kyle |
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#2
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On Fri, 03 Sep 2004 22:34:11 GMT, "Kyle.B.H" wrote:
In the two years I've had my bike, the front shifting (shimano STI triple), has never been great. The major problem has been that the front derailer bottoms out against the seat tube before it can push the chain onto the granny. And while I've had success getting it to work, the adjustment is _extremely_ sensitive, such that when I make any sort of drivetrain change, it can be a nightmare to get working properly again. My question is - is this likely an issue with my braze-on? This is a hand-made frame, so could it be that the braze-on is not allowing the proper distance between f.der and seat tube? I've tried two different deailers with the same result. I could go with a wider bottom bracket, but that would mess up my chainline. Is there a 'standard' for the seat tube to derailer (say, the mounting bolt) distance? I'm seriously considering removing the braze-on so that I can use a clamp-on front derailer. I'm sure an hour or so with my hacksaw and dremel would take care of it nicely, albiet leaving a nasty scar on my beautiful frame. Any tips? I've considered going to friction or Campy front shifting, but if the derailer can't move in far enough, those solutions won't help. Thanks, Kyle Shimano triple chain line spec is 45mm +/-1.5mm. If yours is less, then a longer spindle is a good idea and should help reduce the problem. Shimano spec for the lateral distance between the bike's center plane and the center of the braze-on slot is somewhere around 25mm. This is from memory, so might be +/- a millimeter or so. But braze-on position doesn't sound like the issue; you say the derailleur hits the seat tube. Moving the braze-on won't move the seat tube out of the way. ;-) Considered filing the derailleur? You might be able to get another millimeter or two of travel. Considered asking the builder to add a careful dent on the seat tube? Many new bikes come with intentional dents from the factory. |
#3
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On Fri, 03 Sep 2004 22:34:11 GMT, "Kyle.B.H" wrote:
In the two years I've had my bike, the front shifting (shimano STI triple), has never been great. The major problem has been that the front derailer bottoms out against the seat tube before it can push the chain onto the granny. And while I've had success getting it to work, the adjustment is _extremely_ sensitive, such that when I make any sort of drivetrain change, it can be a nightmare to get working properly again. My question is - is this likely an issue with my braze-on? This is a hand-made frame, so could it be that the braze-on is not allowing the proper distance between f.der and seat tube? I've tried two different deailers with the same result. I could go with a wider bottom bracket, but that would mess up my chainline. Is there a 'standard' for the seat tube to derailer (say, the mounting bolt) distance? I'm seriously considering removing the braze-on so that I can use a clamp-on front derailer. I'm sure an hour or so with my hacksaw and dremel would take care of it nicely, albiet leaving a nasty scar on my beautiful frame. Any tips? I've considered going to friction or Campy front shifting, but if the derailer can't move in far enough, those solutions won't help. Thanks, Kyle Shimano triple chain line spec is 45mm +/-1.5mm. If yours is less, then a longer spindle is a good idea and should help reduce the problem. Shimano spec for the lateral distance between the bike's center plane and the center of the braze-on slot is somewhere around 25mm. This is from memory, so might be +/- a millimeter or so. But braze-on position doesn't sound like the issue; you say the derailleur hits the seat tube. Moving the braze-on won't move the seat tube out of the way. ;-) Considered filing the derailleur? You might be able to get another millimeter or two of travel. Considered asking the builder to add a careful dent on the seat tube? Many new bikes come with intentional dents from the factory. |
#4
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Kyle.B.H wrote:
In the two years I've had my bike, the front shifting (shimano STI triple), has never been great. The major problem has been that the front derailer bottoms out against the seat tube before it can push the chain onto the granny. And while I've had success getting it to work, the adjustment is _extremely_ sensitive, such that when I make any sort of drivetrain change, it can be a nightmare to get working properly again. My question is - is this likely an issue with my braze-on? -snip- Any tips? I've considered going to friction or Campy front shifting, but if the derailer can't move in far enough, those solutions won't help. That's a regular situation with Shimnao fronts. Campagnolo fronts have a different issue- the anchor hits the frame when you shift to high gear. It is really tough to remove material as the spring mount is what hits. A slight chainline adjustment, adding a 2mm spacer under the right cup, may help. Changing to bolted format won't help. I'm no fan of braze fronts but that isn't the cause of this. It's sometimes possible to judiciously bend the cage such that the outer plate hits the chain sooner at a point toward the rear of the cage. An experienced mechanic can do that quickly. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971 |
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Kyle.B.H wrote:
In the two years I've had my bike, the front shifting (shimano STI triple), has never been great. The major problem has been that the front derailer bottoms out against the seat tube before it can push the chain onto the granny. And while I've had success getting it to work, the adjustment is _extremely_ sensitive, such that when I make any sort of drivetrain change, it can be a nightmare to get working properly again. My question is - is this likely an issue with my braze-on? -snip- Any tips? I've considered going to friction or Campy front shifting, but if the derailer can't move in far enough, those solutions won't help. That's a regular situation with Shimnao fronts. Campagnolo fronts have a different issue- the anchor hits the frame when you shift to high gear. It is really tough to remove material as the spring mount is what hits. A slight chainline adjustment, adding a 2mm spacer under the right cup, may help. Changing to bolted format won't help. I'm no fan of braze fronts but that isn't the cause of this. It's sometimes possible to judiciously bend the cage such that the outer plate hits the chain sooner at a point toward the rear of the cage. An experienced mechanic can do that quickly. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971 |
#6
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none- The major problem has been that the front derailer
bottoms out against the seat tube before it can push the chain onto the granny. BRBR My question is - is this likely an issue with my braze-on? BRBR Issue with the seattube width/BB shell placement. Try a spacer under the right BB cup, a 'small' dent in the seattube, a grindaway on the front der where it hits the seattube. Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302 (303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene" |
#7
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none- The major problem has been that the front derailer
bottoms out against the seat tube before it can push the chain onto the granny. BRBR My question is - is this likely an issue with my braze-on? BRBR Issue with the seattube width/BB shell placement. Try a spacer under the right BB cup, a 'small' dent in the seattube, a grindaway on the front der where it hits the seattube. Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302 (303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene" |
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