So my newish road bike (not more than 1500 miles on it) has suddenly developed an alarming screeching noise, plus frame vibration, if I stomp hard on the left pedal at the top of the stroke when on the big chainring. Tracking it down is proving a headache…
Obvious guess 1: Chain grating against the side plate of a badly adjusted front mech – but extensive fiddling with the cable tension failed to make any noticeable difference.
Obvious guess 2: Excessive play in the bottom bracket, an FSA external bearing job with a very poor reputation – but all seems in order here.
Obvious guess 3: Rear wheel flexing and rubbing against the frame or brake pads – but I can’t see any sign of flexing, and it definitely feels and sounds like metal-on-metal, not metal-on-rubber.
Anything else I should check before I take it into the LBS with a sheepish expression?
Diagnosing a mystery noise, again
Re: Diagnosing a mystery noise, again
Rear axle broken? Still held together by q/r.
You may have already eliminated that possibility,depending on how you've determined that the rear wheel isn't flexing.
You may have already eliminated that possibility,depending on how you've determined that the rear wheel isn't flexing.
High on a cocktail of flossy teacakes and marmalade
Re: Diagnosing a mystery noise, again
Sometimes it is difficult to find a problem with the BB with the chain still fitted. With the chain removed problems become very apparent. Having a means of easy chain removal is important when maintaining bikes, hence the popularity of so-called quick links.
I should coco.
Re: Diagnosing a mystery noise, again
Chain-wheel teeth catching on chainstay? - your description "metal-on-metal" could describe something terminal if not located.
Your "obvious guess" 1 - it's front cage position to check, as well as cable tension - in fact I'm not sure that the latter in itself would be the problem.
"obvious guess" 2 - if you've checked the BB when the bike is at rest, you won't know what movement there is when pedalling, particularly when pedalling hard - and I've known very slight movement on bikes with very tight clearances cause chainrings to catch on chainstay, when at rest there looks to be enough clearance. You'll have to look very close for any marking on the chainstay to be evident, because it'll be hidden by the chainring.
If there are any tight clearances, then remember that the frame will flex under pedalling load, and clearances that are clearances when at rest can cease to be clearances when the frame is under pedalling load.
The same can go for the rear wheel - check that the tyre has enough clearance between it and the mudguards, particularly the stay-fixing brackets - the rear wheel can flex more than you think, again under pedalling load.
You will let us know when you've final found it, won't you?
Your "obvious guess" 1 - it's front cage position to check, as well as cable tension - in fact I'm not sure that the latter in itself would be the problem.
"obvious guess" 2 - if you've checked the BB when the bike is at rest, you won't know what movement there is when pedalling, particularly when pedalling hard - and I've known very slight movement on bikes with very tight clearances cause chainrings to catch on chainstay, when at rest there looks to be enough clearance. You'll have to look very close for any marking on the chainstay to be evident, because it'll be hidden by the chainring.
If there are any tight clearances, then remember that the frame will flex under pedalling load, and clearances that are clearances when at rest can cease to be clearances when the frame is under pedalling load.
The same can go for the rear wheel - check that the tyre has enough clearance between it and the mudguards, particularly the stay-fixing brackets - the rear wheel can flex more than you think, again under pedalling load.
You will let us know when you've final found it, won't you?
Re: Diagnosing a mystery noise, again
gaz wrote:Rear axle broken? Still held together by q/r.
Is there an easy way to check this, or does it involve taking the wheel to bits?
JohnW wrote:If there are any tight clearances, then remember that the frame will flex under pedalling load
Sure, but it’s a stiff aluminium frame which wasn’t previously causing any trouble. So I’m looking for problems that might have developed through wear and tear. No mudguards so no especially tight clearances.
Anyway, thanks for the suggestions. I’ll take the chain off tomorrow and have a close look at the BB and any possible contact between chainring and chainstay.
Re: Diagnosing a mystery noise, again
JamesE wrote:gaz wrote:Rear axle broken? Still held together by q/r.
Is there an easy way to check this, or does it involve taking the wheel to bits?....................
What I'd do is take the wheel out, remove the QR skewer and you'll find that the spindle will simply pull out of the hub at each end - pull at the locknuts and the two parts will come out..............that's if the spindle is broken.
The old, traditional rear hubs, with screw-on freewheel blocks were more prone to this problem, but current production freehubs, with the bearings more evenly spaced, are less likely to break spindles. You gotta try everything though.
Another thought - it's not a problem in your pedal bearing is it?
Depending upon how old you are, it could be your left knee
!Re: Diagnosing a mystery noise, again
I have an aluminium audax bike. I find it amplifies any minor noise to an alarming extent.
On one audax ride it developed a horrible creaking noise. There was no obvious fault with BB cranks or any other moving part and I was looking for a crack around the bottom bracket. Eventually I traced it to some slight movement in the mudguard bridge.
BTW on one occasion I found a creaking noise due to the rear QR being insufficiently tightened (vertical dropouts).
On one audax ride it developed a horrible creaking noise. There was no obvious fault with BB cranks or any other moving part and I was looking for a crack around the bottom bracket. Eventually I traced it to some slight movement in the mudguard bridge.
BTW on one occasion I found a creaking noise due to the rear QR being insufficiently tightened (vertical dropouts).
Re: Diagnosing a mystery noise, again
Problem tentatively solved. It seems to have been a combination of things: a bit of chain rub against a slightly misadjusted front mech cage, plus a bit of brake rub against a flexing back wheel, amplified by wet-weather riding getting road crud on the brake blocks and making them scrreeeechyyyyyyyy as hell. Not the first time a mechanical problem's been not one thing completely out of whack, but the cumulative effect of several things a bit out of whack.