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Rear derailleur: Noisy smallest sprocket
#1
Hi everybody out there!
This is my first post here.

I have a Trek 3700, no mods, with the original free wheel sprockets MF-TZ31 and Altus rear derraileur, 7 gears, and Shimano EF50 Shifters.

I think my RD is properly adjusted, all the gears shift ok, but when using the smallest sprocket, and exerting a huge torque on the pedals, i hear a noise, like when the chain is getting out of a sprocket and trying to shift to the next one, but i think my gears are well adjusted. The limiter screws are adjusted, the guiding pulley is aligned with the smallest sprocket and the barrel is adjusted so my gears shift ok, but i still get that annoying sound.
I think the problem is in the guiding pulley, that it seems slightly out of plane with the sprockets (tilted in the vertical axis), but i don't know if this is normal. It's strange that the sound appears only when applying a powerful torque. With adjustment the sound went off for a time, but it came on again.

Do i need more fine adjustments?, can be something wrong with my derraileur? (the technician told me it was ok), May i need to adjust the B screw???

Thanks...
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#2
Are you sure it's not the chain rubbing on the front deraileur cage? When you put a lot of pressure on the pedals the frame and crankset flexes and is deflected a little, sometimes enough to make the front chainring and the chain move enough to rub on the front deraileur cage.
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#3
Xerxes might be right and it could also be the chain hitting the inside of the large chainring. Does it do the same thing when you are in the large in front or only small? But a few other thoughts: If the pulley sits at an angle, it could be that the pulley itself is worn. Not sure why that would make noise, but it's possible. If it is the whole derailleur that sits at an angle and not just the pulley, it could be a bent derailleur or derailleur <i>hanger</i> on the frame.
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#4
Hi.... Thank for your answers. They gave me a lot of new things to check to try to find the problem. DaveM, it sounds only when the chain is in the large front chainring and the smallest sprocket.
Yesterday I rechecked the hi limiter screw, and adjusted it so the chain gets away from the 6th sprocket. Also, rechecked the front derailleur settings, and it looks ok, because there is a big clearance between the chain and the derailleur cage, even in the extreme positions. Time ago, a technician checked my derailleur and it seemed ok, and it isn't misplaced. Tomorrow i'll take my bike to the street to stress it and check if it's better now. Thank you all.
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#5
Check that the cassette is on correctly. Secondly check your high limit screw. In a stand, let all the slack out of rear shifter. chain now in small cog. The chain should instantly drop into the small cog as you pedal with you hand and push up on the derailleur and then let drop down.
GO RIDE...
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#6
Hi!
Guys you're awesome. I finally repaired my bike by using your advices. The problem was that the front derailleur was deflecting and rubbing on the chain. With little stress that didn't happen, but today i put a lot of pressure on the pedals while applying brakes, and the crankset and derailleur flexed enough to rub the chain and make that weird noise. Finally, i adjusted limiter screws and barrel tensor, so that the chain-cage clearance got higher than recommended by Shimano. The noise stopped, and it still shifts ok. The deflection is really greater than i expected. I suppose that I stomp the pedals heavier that most of people.
Now my bike is riding smoother than ever, and I love her again.
Thanks a lot, Greetings from Chile.
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