Can you help me diagnose a knocking sound as I peddle

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gingemonster
Posts: 2
Joined: 16 Sep 2020, 1:32pm

Can you help me diagnose a knocking sound as I peddle

Postby gingemonster » 16 Sep 2020, 1:39pm

I need help diagnosing a knocking noise as I peddle, here are the symptoms:

  • Ribble gran fondo with new SPD-SL pedals
  • As the left hand peddle starts to come over the top of its path there is a knocking sound that is reasonably loud
  • It happens more and is louder the harder I push, especially if I stand up when going uphill
  • If I freewheel with my left foot and only peddle with my right it stops instantly
  • It seems to happen more at lower speed but changing gear makes not obvious difference
  • It happens if I am clipped in or not
  • It seems to reduce or go away completely after about an hours riding
  • It really feels like the knocking is directly under my foot but of course may just be transmitting through the crank


What I have tried

  • tightening the crank on the left
  • tightening the clip tension

I'm very new to taking cycling seriously and road bikes at all this so please excuse my ignorance especially in the names of components etc. Thanks for any help and advice

Jdsk
Posts: 2373
Joined: 5 Mar 2019, 5:42pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby Jdsk » 16 Sep 2020, 1:52pm

Welcome.

What an excellent description.

Get hold of the pedals by hand and give them a good wiggle in all directions including towards and away from the bike and rotating them. Is the L looser than the R?

Were the pedals done up tight against the cranks?

Can you add some photos of the pedals?

Sheldon Brown: "Bicycle Pedals":
https://www.sheldonbrown.com/pedals.html

Park Tool Repair Help for pedals:
https://www.parktool.com/blog/repair-help?query=&area%5B%5D=57

Jonathan

gingemonster
Posts: 2
Joined: 16 Sep 2020, 1:32pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby gingemonster » 16 Sep 2020, 2:02pm

Hi

Thanks for the quick reply

Yes peddles were done up tight but not overly and seem plenty right now when I checked previously, pretty sure they are not moving but I will double check when I get home. Here are photos I took this morning

Thanks
Brian
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roubaixtuesday
Posts: 3290
Joined: 18 Aug 2015, 7:05pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby roubaixtuesday » 16 Sep 2020, 2:15pm

Random thoughts and suggestions.

It's pretty unlikely to be the pedal itself. Do you have access to another pair of pedals to swap in and test?

Bottom bracket may be most likely? Take the chain off and rotate and wiggle the cranks. Any play there?

Issues with rear wheel could manifest in this sort of way too. Any play in the bearings? Is the QR securely tightened?

Brucey
Posts: 40543
Joined: 4 Jan 2012, 6:25pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby Brucey » 16 Sep 2020, 2:50pm

LH crank is possibly loose. Retightening the pinch bolts is often like bolting the stable door; often the spline in the crank is damaged (from being ridden on, it doesn't take long) and no amount of retightening will fix it.

I would suggest that you remove the LH crank and assess the wear on the spline. A new LH crank may be required.

OTOH it might be something else entirely....

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

greyingbeard
Posts: 826
Joined: 24 Mar 2015, 10:41pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby greyingbeard » 16 Sep 2020, 2:55pm

It will be a council official tapping his clipboard and tutting loudly if you don't have a Peddlers Licence.

simonhill
Posts: 3070
Joined: 13 Jan 2007, 11:28am
Location: Essex

Re: Can you help me diagnose a knocking sound as I peddle

Postby simonhill » 16 Sep 2020, 3:53pm

Have you had the pedals off?

I have had a tiny bit of grit in the pedal threads cause a clicking sound. Yours sounds more than that, but could be worth checking.

Remove pedal and ensure both threads are completely clear. Grease and refit.

peetee
Posts: 2346
Joined: 4 May 2010, 10:20pm
Location: Cornwall

Re: Can you help me diagnose a knocking sound as I peddle

Postby peetee » 16 Sep 2020, 5:03pm

Is this with cleated shoes? If so ride in a pair of trainers and see if the prob is still there. If as you have suggested it’s not to do with the cleat it could be the shoe sole.
Current status report:
Back on two wheels in deepest Pastyland and loving every minute. Mission: to enjoy big, bad hills again.

slowster
Posts: 1605
Joined: 7 Jul 2017, 10:37am

Re: Can you help me diagnose a knocking sound as I peddle

Postby slowster » 16 Sep 2020, 5:13pm

Check that all the chainring bolts are tight. Check also that the cassette lockring is tight and that there is no side to side play of the cassette sprockets on the freehub.

chris_suffolk
Posts: 485
Joined: 18 Oct 2012, 10:01pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby chris_suffolk » 16 Sep 2020, 7:29pm

Sounds like bottom bracket to me, had the same symptoms on a couple of bikes. Could never feel any roughness in the cranks, but once I took the bearings out they were clearly rough and needed replacing.

Jdsk
Posts: 2373
Joined: 5 Mar 2019, 5:42pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby Jdsk » 16 Sep 2020, 7:32pm

chris_suffolk wrote:Could never feel any roughness in the cranks, but once I took the bearings out they were clearly rough and needed replacing.

I was very surprised by precisely that recently. Shimano SM-BB51.

Jonathan

rogerzilla
Posts: 1423
Joined: 9 Jun 2008, 8:06pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby rogerzilla » 16 Sep 2020, 9:11pm

How did you install the pedals? The recommended torque is 35-55 Nm. A 6mm allen key can't do it, and an 8mm barely can. I use an 18" torque wrench with a 3/8" allen bit, and even that takes a fair bit of oomph.

hoppy58
Posts: 278
Joined: 9 Mar 2011, 3:07pm

Re: Can you help me diagnose a knocking sound as I peddle

Postby hoppy58 » 17 Sep 2020, 1:49pm

We had the same problem on our tandem and I went through all the same checks, pedals, chainrings, crank bolts, bottom bracket, stiff chain links etc etc, but still a click every pedal revolution. Do you know what it was in the end...the brake cable loop was sticking out slightly and the stokers heel just clipped it every revolution!! I adjusted it and now we cycle in perfect silence!! Moral of the story is just to check unlikely sources for the noise.