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Grinding noise. when shifting to low gear on bicycle? |
I bought a bike from walmart and decided to give the bike a test drive......the chain seems to rub against the drive train when i shift to a lower gear (faster, lightest peadling)....there is a lot of grinding and it doest go away. What is wrong and what do i do? The bike has a front and a rear derailleur that pushes the chain over the gear sprockets when you shift. Grinding occurs when the derailleur is dropping the chain into a position it thinks is DIRECTLY over the sprocket but the alignment is slightly off. There are a few possible remedies - the first thing you have to do is determine if the grinding is coming from the front derailleur or the back. Each derailleur has screws that control the minimum and maximum reach of the derailleur. These were set in the factory but sometimes need to be adjusted when the bike comes out of the box. As another answerer suggested, if the bike has index ("click") shifting the control screws are harder to find and adjust, but these usually don't fall out of alignment as easily, so the problem is usually caused by a bent or out-of-position derailluer. (it isn't as serious as it sounds) Here is a trick that I used to fix most grinding derailleurs that came into the bike shop - it fixes the problem almost every time: stand behind the bike so you are looking directly down the chain. For a grinding rear derailleur, look at the position of the derailleur to see if it is straight up and down - the derailleur will grind if it is feeding the chain to the sprocket at an angle (even a slight angle). Use a large set of pliers to GENTLY bend the derailleur until is is straight. They often get bent when they are put in the box or layed down on the gears. For a grinding front derailleur, make sure the arm of the derailleur is parallel to the chain. If it is angled, loosed the derailleur where it is clamped to your seat tube, realign it and re-tighten. (you shouldn't need to bend a front derailleur unless it has been dropped and damaged) To keep your derailleurs from bending, always lay a bicycle down GEAR-SIDE-UP. Good luck. Source(s): I used to be a bike mechanic at Frank's Spoke-n-Wheel There are usually two derailleurs on the bike: one up front for the chainwheel, and one in back for the rear cassette. If the grinding kicks in as you shift to the bigger cogs on the rear cassette, most likely your front derailleur is dragging against the chain. That's a common glitch; try shifting the front derailleur around a bit. If your bike has "index" shifting, where each shift is a "click" on the selector, you'll want to have a bike mechanic adjust the derailleur so it doesn't drag on the chain. It's your knees. You should be in a wheelchair, not on a bike. |
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