transmission noise

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transmission noise

Postby Tom » 23 Apr 2020, 11:55am

Hallo yet again,

Thorn Sherpa.

Still looking for a a mysterious noise I think is coming from my transmission every rotation of the cranks, I have replaced/checked all I can think of,including replacing my bottom bracket bearings Shimano UN 54 square axle type I've checked, replaced front mech Shimano 9 speed XT the sound is like the chain is slightly catching the front mech as the crank rotates once, have double checked this, on my bike stand no prob even tried the old dodge of applying rear brake slightly to rotate the the crank under pressure nothing doing, tried another seat my seat Brooks, tried plastic one, checked chain rings for tightness, rings no buckle on any of them
All seems ok until I go for a ride and put pressure on pedals Just ordinary pressure,

Forgot to say I bought a new frame from Thorn Cycles and have been rebuilding it, could the Bottom Bracket that I bought be slightly to long or short causing slight chain problems.

Yours at a loss Tom

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Re: transmission noise

Postby mig » 23 Apr 2020, 11:57am

changed pedals? changed shoes?

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Re: transmission noise

Postby reohn2 » 23 Apr 2020, 12:31pm

Left or right pedal on the down/power stroke?

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Re: transmission noise

Postby Brucey » 23 Apr 2020, 12:59pm

Tom wrote:…. checked chain rings for tightness,...

IME you can't be 100% certain it isn't the chainring bolts until you have removed the chainrings, cleaned everything, and then carefully reassembled.

When you reassemble the chainrings, use grease in two places only;

1) on the chainring bolt threads and

2) a small amount on the head of the chainring bolt (the part that moves when you tighten it)

do not use it on the chainring interfaces or on the outside of the female part of the bolts.

The other thing that is always worth doing is removing the pedals and cleaning/regreasing the pedal threads.


Posts: 212
Joined: 23 Jan 2007, 7:54pm

Re: transmission noise

Postby Tom » 23 Apr 2020, 1:55pm

well chaps thanks for your suggestions,

Already did the pedal checks didn't change things,changed the rear mech still the same,upgrading chain set anyway next Brucy so fingers crossed

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Re: transmission noise

Postby peetee » 23 Apr 2020, 1:59pm

If you are using SPD shoes check to see if the reinforcing plate in the sole has fractured.
Winter had arrived in the land of Kernow. Along with it came wet roads and cool winds.
“Oh, my wheels and coupling rods!” Peetee exclaimed.

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Chris Jeggo
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Re: transmission noise

Postby Chris Jeggo » 24 Apr 2020, 12:49am

Does it only happen in top gear? I had that happen once, a click once per crank revolution. I was using track cranks (with a single chainring) with gears, and when everything flexed a bit under pressure, the clearance between chain and crank became negative. It took me a while to find. The little marks near the end of the RH crank were what eventually gave it away.

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Re: transmission noise

Postby francovendee » 24 Apr 2020, 7:18am

I had something like this back in the winter. I couldn't pin it down and tried replacing pedals, bottom bracket. Stripping, cleaning and re-assembling the chainrings. I checked all other screws for tightness. None of this cured it and I ended up just putting up with it.

The noise just disappeared on it's own. I've still no idea what was the cause and just hope it won't come back.

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Re: transmission noise

Postby sjs » 24 Apr 2020, 7:45am

Headset, stem, or spacers in that area? Seatpin/frame interface? Wheel/dropout interface (perhaps loose quick releases)?

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Re: transmission noise

Postby Tigerbiten » 24 Apr 2020, 11:36am

Sometimes it's not where you think.

A transmission noise I tracked down was caused by my clipless pedals.
Under power my feet rotate sideways a little per stroke.
If a little grit got between the pedal and my shoe, it caused a creak.
A quick polish of all surfaces and no noise.

Luck ............ :D