What's that occasional thunking?

does the 'bump' occur in the same place through your pedal rotation every time? even when you change gears?

i have that exact problem...on a fairly new bike nonetheless [img]cyclingforums.comconfused.gifOpen ↗[/img]
It must be either the chain, the bottom bracket, or the pedals.

It could be your saddle height. I'm by no means an expert in biomechanics but incorrect position, especially seat height and fore-aft position of the saddle can create some major problems with your leg joints.

Darkhorse85 said:

does the 'bump' occur in the same place through your pedal rotation every time? even when you change gears?

i have that exact problem...on a fairly new bike nonetheless [img]cyclingforums.comconfused.gifOpen ↗[/img]
It must be either the chain, the bottom bracket, or the pedals.

Thanks, Darkhorse85. I'll suggest these areas be looked at when I bring it in. It really helps not to go in empty-handed. Interesting that your bike is also new.

diehard said:

Thanks, Darkhorse85. I'll suggest these areas be looked at when I bring it in. It really helps not to go in empty-handed. Interesting that your bike is also new.

P.S. Although I haven't carefully tracked it, yes, it seems to be occurring in the same place.

bobbyOCR said:

It could be your saddle height. I'm by no means an expert in biomechanics but incorrect position, especially seat height and fore-aft position of the saddle can create some major problems with your leg joints.

Although a "body scan" was employed for correct fit, the seat has been adjusted up and down, so that's worth checking. Maybe when it's right, I'll mark the spot with an indeliible marker. Thanks for the idea.

I think it would be unlikely to be you knee or hip. one possibility i can think of is that maby the free hub aint tight, and it turns slightly under load. which is normal on a new bike. As we say in maintenance, if you cant see whats wrong with it. just keep going till it realy breaks. Then youll know.

Hi Insaneclimber. Is "Wait till it really breaks..." the same as "If it ain't broke, don't fix it (yet?) I think I'm out of my league. I can imagine "it" eventually breaking as I go flying off my bike, knowing finally what he problem really was. Still, I'm glad to know you don't think it's me that's causing it. Thank you.

I notice that nobody so far has suggested checking the fit/tightness of the cranks on the bottom-bracket axle, for "float" in the bottom bracket itself, or even for a loose bottom-bracket cassette.

If either crank isn't really tight on the axle, this will always manifest itself at the left crank, for obvious reasons.

You can check for float in the bottom bracket by getting a mate (or bike-stand) to hold the bike while you rock either crank at right-angles to the plane of the b.b. axle. This will also show up whether the b.b. cassette (if you have one) needs a slight graunch with a spanner.

Anyway it's always a good idea to run over the bike with spanners, Allen keys and screwdrivers at least once a week, and especially if you've just re-built it.

Totally off the topic, I recall that many years ago Barry Hoban had appalling knee problems. They went on for weeks, and were finally tracked down to a a minutely out-of-plane pedal spindle.

As the old song says, "little things mean a lot".

Good Luck

:eek: John :eek:

Dear John. I'm impressed by the depth of your analysis on the basis of my somewhat vague description. This is great ammo to bring to the bike shop next week. I'll report back once I know something. Thanks for taking the time to respond.
M

john, youre right!

i just came back to this thread to report that i discovered that my bottom bracket was loose, and that is what was causing the thump. i can almost wiggle the crank arm in and out. under close inspection, it's the actual bottom bracket sealed cartridge itself which is moving.

...now all i gotta do is find out how to tighten it...

from wikibooks:

Quoted post said:

Symptoms of a bottom bracket needing overhaul

If your bike develops a periodic creak or ticking noise from the bottom bracket when under high or even normal load, it could be time to regrease the bottom bracket shell. The creaking can be caused by the on-set of corrosion (due to frequent exposure of the bottom bracket to water). Usually it's enough to replace the contaminated grease by removing the bottom bracket, cleaning it and the shell with degreaser and regreasing it with water proof anti-seize grease (Bicycling.com and ehow.com).

I must tell this "I was a pratt" story.

I built my first "real racer" in 1947/48 ("One piece at a time", as per Johnny Cash) based on a 1939 Dawes frame. I was 14 at the time.

Lubrication to head, hubs and bottom bracked was by grease gun: once you saw grease exuding, you stopped.

Each week the head (2 nipples) and hubs got a pump or two, but the bottom bracket always seemed to need more before the little tell-tale snot appeared where the axle poked out.

About three years later I decided to re-paint the frame. I stripped everything down, and took the paint off with a paraffin blowlamp (not too hot a flame). As I started burning the paint off the seat tube, there was a frying noise, and a large sausage of grease appeared in the bottom-bracket void.

I salvaged this and carried on: more grease appeared, and more, and more, and the same thing happened with the down tube.

Because the bottom bracket was open to both seat and down tubes, that's where the grease had been going - about a pound up each tube.

Yer live and learn!

😕 John 😕

Darkhorse85 said:

john, youre right!

i just came back to this thread to report that i discovered that my bottom bracket was loose, and that is what was causing the thump. i can almost wiggle the crank arm in and out. under close inspection, it's the actual bottom bracket sealed cartridge itself which is moving.

...now all i gotta do is find out how to tighten it...

from wikibooks:

Didn't you say the mechanic at the bike shop tested it, that guy must be a moron, i wouldn't go there again.

My old Dad used to say "Well boy, there's mechanics and there's muckanics...." - a fancy overall with a logo over the pocket doesn't always mean membership of the first group.

🙂 John 🙂

Insaneclimber said:

Didn't you say the mechanic at the bike shop tested it, that guy must be a moron, i wouldn't go there again.

Dear Insaneclimber and Darkhorse,

I don't believe I said he was a mechanic. He helped me when I was test-riding it and outfitting it before purchase; he also adjusted the fit. He is in no way a "moron," He just didn't experience the "thunking" when he rode it around the block, and it would be uncivil to call him that even if it were true.

Thunking appears to be caused by the rider, not the bike. As I suspected, uneven pedaling is the culprit. Thanks anyway.

Darkhorse85 said:

does the 'bump' occur in the same place through your pedal rotation every time? even when you change gears?

i have that exact problem...on a fairly new bike nonetheless [img]cyclingforums.comconfused.gifOpen ↗[/img]
It must be either the chain, the bottom bracket, or the pedals.

Hi Drkhorse,

Thunking appears to be caused by the rider, not the bike. As I suspected, uneven pedaling is the culprit. Thanks anyway.

bobbyOCR said:

It could be your saddle height. I'm by no means an expert in biomechanics but incorrect position, especially seat height and fore-aft position of the saddle can create some major problems with your leg joints.

Thunking appears to be caused by the rider, not the bike. As I suspected, uneven pedaling is the culprit. Thanks anyway.

John Knees said:

I notice that nobody so far has suggested checking the fit/tightness of the cranks on the bottom-bracket axle, for "float" in the bottom bracket itself, or even for a loose bottom-bracket cassette.

If either crank isn't really tight on the axle, this will always manifest itself at the left crank, for obvious reasons.

You can check for float in the bottom bracket by getting a mate (or bike-stand) to hold the bike while you rock either crank at right-angles to the plane of the b.b. axle. This will also show up whether the b.b. cassette (if you have one) needs a slight graunch with a spanner.

Anyway it's always a good idea to run over the bike with spanners, Allen keys and screwdrivers at least once a week, and especially if you've just re-built it.

Totally off the topic, I recall that many years ago Barry Hoban had appalling knee problems. They went on for weeks, and were finally tracked down to a a minutely out-of-plane pedal spindle.

As the old song says, "little things mean a lot".

Good Luck

:eek: John :eek:

Thunking appears to be caused by the rider, not the bike. As I suspected, uneven pedaling is the culprit. Thanks anyway.