Bicycle Mechanics - Bent tab
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06-03-10, 05:09 PM
My wife has a 80's model Miyata Tri Cross that she loves to death. She's had it since it was new. She bought herself a Merceir road bike to use in triathlons but didn't feel quite right on since it has been a long time since she was on a bike. She wants to restore the Miyata and use that to train on and get compfy with and then switch back to the Merceir. Here's the problem. On the bottom of the chain stay where the rear derailer attaches to the frame the tab (for lack of a better word) is bent in approximately 1/4 inch casuing the derailer to rub against the spokes. I was just going to place it into a vice and straigten it back out however she said that it would not be safe to ride. I was going to do this very slowly so as not to cause any more stress on the metal if there even is any. Any thoughts? Can I do this with out causing any damage?
So if she won't let you straighten it, how does she propose that it be fixed? Magic?
Is it a steel frame? Aluminum? In general these are safe to bend back, provided (in the case of aluminum) it's not bent too bad. But the problem is getting it truly parallel to the wheel. Bike shops have special tools that let them bend it and measure the result against the wheel rim. You can get it close enough to ride, but the shop is the ultimate solution.
Btw, why isn't she comfortable on the Mercier? Does it fit her?
06-03-10, 05:54 PM
"80's model Miyata", that says "steel frame" to me.
Bending the derailleur hanger back is a fairly simple job but, as in all things, the devil is in the details.
If you can't bend it back by hand with the derailleur in place, see if you can clamp a big adjustable wrench around the derailleur and hanger together. If you remove the derailleur before attempting to straighten the hanger, you take the risk of ovalizing the derailleur hanger hole. I don't know how to fix that.
You want the hanger to be parallel to the bike's main frame. The more closely spaced your rear cogs, the more accurate the hanger alignment has to be. On a 5, 6 or 7 speed bike I can eyeball the alignment adequately. With 9 or 10 rear cogs, I use an alignment tool. If you're not confident doing it yourself, it should only be a $15.00 or $20.00 job at any average or better bike shop.
06-03-10, 06:16 PM
Take it to the shop. With the proper tool straightening a derailleur hanger only takes a minute.
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