Bicycle Mechanics - Bent Dura Ace Cage
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07-03-11, 06:35 PM
I just picked up a complete dura-ace 7700 9 spd group set for a good price with quite a few extras (couple seat posts, extra front-d, saddle, crankarm..) However The rear derailleur cage got bent while in his garage. And I was wondering if it would be possible to bend it back (my first plan), use it as is, get a replacement cage, etc. I think if Im careful I should be able to bend it back because its only a slight bend with no creases. Ive heard that the cages are pretty interchangeable on several models, but I cant seem to find replacements for any of them. Any ideas?
07-03-11, 10:42 PM
What do you have to lose? Just try and bend it back. Worst case is that the cage is aluminum and cracks. Best case, it's steel and is close to like new after a slight tweak. Replacement parts are likely impossible to find but you can probably buy a used 7700 rear derailler off Ebay and swap parts as necessary.
For the bending operation, I'd recommend removing the cage first so that you don't inadvertently stress any other part of the derailler while tweaking the cage. A vice and a straight edge to use as a guide will be useful tools for the repair.
You really can`t use it as is. A bent derailleur cage will give the same issues as a bent hanger.
Suggest you strip it down and see what you can do. Doubt there`s any steel in any DuraAce derailleur so take your time and don`t heat anything. The parts are probably heat treated.
If you have good eyes and hands you should be able to bend it back, to just about as good as new. About the only cages that can't be straightened are carbon fiber ones. Steel and aluminum cage plates both respond very well to some gentle persuasion.
It's key that you get both pulleys into a common plane, then the cage as a whole square with the pivot bolt (in plane with the wheel). Take it slow so you're not working back and forth and the structure shouldn't suffer.
While others may say aluminum can't be straightened, note that you have little to lose trying since it's not usable as is, and worst case scenario if it does break isn't so serious. After all it's not an airplane part.
07-04-11, 08:59 AM
unfortunately it is aluminum which is why I haven't jumped right into straightening it. But like I said, its pretty mild and I have access to a good shop, so I think its possible. The guy had an extra outer cage he gave me, but I must have left it at his house and its an hour drive away. Im hoping he sells me the bike in the corner of his garage so I have an excuse to go back and get that outer cage. Are the cages from any other model shimano derailleurs interchangeable? Ive seen really cheap 105's, etc. Thanks.
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