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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 07-16-07, 03:09 PM   #1
GTX723
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Cannondale needs new cranks

I've been riding my '91 3.1 series for 16 years... but now I have to get a new crank. The pedal shafts wiggle in their sockets. Each year for the last four or so I've fugded it by making a shim from a strip of aluminum from a beer can, but I've had it this year.
What do I do? Does a SHimano fit on a Cannondale? I have a Shimano deralieur, 7 speed.
No idea what to buy. Ideas?
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Old 07-16-07, 03:42 PM   #2
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Where are you putting this shim? I'm a little confused about it's purpose. If the pedals, even after tightening, were still loose in the crank, it sounds like the crank threads are stripped. You don't necessarily need a new crank to fix this as you could either buy a kit to repair the threads (Helcoil or other type of thread insert kit) or have a shop do it (though this might cost the same as a new crankset).

If you could explain the shim a little more I might have another suggestion.

If you did end up needing to replace the crank, I believe that you have a basic square taper crankset on the bike in which case any non-Campagnolo square taper crankset will fit. Just find one with the same gearing as your current one.
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Old 07-16-07, 04:03 PM   #3
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Shim on the crank

Thank you for the quick reply!!!

The pedal arms are slightly loose in thier sockets.
The square tapers on the end of the pedal arm (is that the crank?) are loose in the square hole. I took the bolt out, then wrapped the square taper with a strip I cut off from a beer can so it would be tight in the square hole, then I put the bolt back in. Now the pedal arm isn't loose.
That doesn't last the year, of course.
I don't understand the stripped part. What would be stripped? I've been riding this for 16 years, but I'm only now learning all the parts vocabulary.
Paul in Merritt Island
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Old 07-16-07, 06:03 PM   #4
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Ok, I understand the problem now and the only fix is a new crankset. I was confused earlier when you said "The pedal shafts wiggle in their sockets." I interpretted this to mean that the actual pedals (where you put your feet) were coming loose from the crank arms (the parts that go from the pedals to the bottom bracket with the right side crank arm having all of the chainrings attached to it). The bottom bracket is that piece with the square tapered end that goes into the crank arms and the crank arms are then bolted to the bottom bracket. The square taper in your crank arms probaly wore out because the bolts came loose and seeing that the aluminum of the crank arms is softer than the steel of the bottom bracket axle, the crank arms deformed. Once the press fit is lost, the arms will never stay tight as you have found.

www.parktool.com is a good website which will help you learn the names of the different parts of the bike and how to fix the issues with those parts when something goes wrong.

So, the fix to your problem is a new crankset. Just be sure to properly torque the crank arms and check the torque after you put in a few hundred miles or so just in case. After that, I wouldn't expect things to loosen up at all.
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Old 07-17-07, 06:29 AM   #5
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The fix to your problem is a new crankset AND a new bottom bracket. You'll need to replace both after rounding off everything around the interface for several years. You'd probably need to get a new BB anyway, to match your new crank.
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Old 07-17-07, 07:48 AM   #6
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Thank you both for your quick responses! I'm at the Park Tool website, looking around. Looks like I'm getting new cranks, and I'll check out the BB, now that I understand what they all are.
My problem was I didn't know if each brand of bike builder used its own crank and BB, or if it was a standard size thing so different aftermarket brands fit, like replacing the Suntour shifters with Shimano shifters. Now I get it.
Thank you!
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Old 07-18-07, 07:53 AM   #7
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I've got a '93 Cannondale that I replaced the crank and BB on earlier this year. I put on an FSA compact crank and FSA BB. It was easy. Make sure you get a 68 mm size BB for your bike.

If you do it yourself, you'll likely need a specialty wrench to tighten the exterior BB cups on a newer style BB/crankset. Of course the wrench depends on the brand/style of BB you get.
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