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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 08-07-10, 08:39 AM   #1
delux68
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crunching drivetrain?

i have a 12 speed 80,s trek 300 elance with light actoin derailleurs and sakae cranks. it shifts though all gears but when i pedal it makes a crunching sound in all gears except the easiest one on the big and small chain rings. i can also feel a shuddering in the pedals. what is the cause of this?
thank you for your time.
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Old 08-07-10, 09:03 AM   #2
wrk101
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Take it to a shop. Could be anything from pedal bearings, to bottom bracket bearings, etc. When is the last time you had the bearings replaced and regreased? And if you are having that done, its a good time to do the wheel hubs as well.

Sounds like BB to me, but diagnosing over the internet is limited.
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Old 08-07-10, 10:31 AM   #3
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Might be beach sand in the grease.
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Old 08-07-10, 10:55 AM   #4
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If you want to solve this for yourself the way to do it is to isolate the various parts that could be causing the issue. To do that first take the rear wheel off the bike. Check the wheel bearings by spinning the rear wheel's axle while feeling for how smooth it is. At the same time gently hold the cassette and turn it backwards to feel for how smoothly the freehub bearings are. Keep in mind that the freewheel pawls will be clicking but the rotation should be smooth and effortless. Next unloop the chain from the crankset rings and hold it so that it's not dragging on the sprockets. Gently turn the cranks and feel and listen for anything unsmooth. Then the pedals. All of these bearing points should be totally smooth and easy to turn with no sign of crunchy or gritty sounds. If any of them are not up to that then replace or service the parts that are rough feeling.

Next are the chain and derrailleur jocky pulleys. The chain should be clean, oiled and totally smooth. Any rusty, draggy or stucking links need to be cleaned with solvent and worked free. If you find any of that in the chain then it's also time to shop for a new chain since rust that makes links sticky will produce faster wear at those points even if you clean and oil them. But if you free them up it'll be fine for a few weeks or months depending on how much you ride. But don't just call it good and move on unless you don't mind the faster overall system wear that will occur. Check the jocky pulleys in the rear derrailleur as well. If those are stiff and packed with grunge then on some gearing combos the chain may well just hop over the stubby teeth and produce what you're describing. Take the cage apart and clean them if that's happening.
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Old 08-08-10, 10:56 AM   #5
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thank you for the reply's. i am a DIY kinda guy so ill try everything that BCRider has mentioned. i just got the bike about two days ago and it was pretty filthy. i cleaned it but it needs some more detailed cleaning of the drivetrain.

Last edited by delux68; 08-09-10 at 07:13 PM.
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