perplexed by new rubbing after bike shop repairs

Quick background, newish ebike, done only 800 miles. It developed a creaking sound when pedaling, but only when doing so with reasonable intensity to engage the freewheel pawl, and no creaking when coasting. I took it to dealer's workshop for repair. I suggested it might be the motor or rear hub but couldn't be sure, they tried their own process of elimination, and agreed with me and replaced the motor under warranty. When I called to chase up the work, they explained the motor was a mess and a gear inside had slipped and wrecked the inners. What baffles me is when I later went to collect it, they told me it was never the motor at all, there was nothing wrong with it (crossed wires with staff?). The mechanic who handed me the bike back said after fitting it a new motor they determined it was actually the rear hub that needed greasing. Expensive mistake on their part... Anyway, the motor was under warranty, so no fee for me and they claimed it was sorted and fine to take home. It definitely got a new motor because the serial number changed in my display!

I brought the bike back home in the boot of the car, but had to take the front wheel off to get it in. I was sloppy and left the wheel propped up against the side of the boot, on the way home, it fell over and bashed the derailleur and bent the hanger. No biggie, I have the tool and was able to get the derailleur aligned once again. Only now I'm riding it again, the original constant creak which I had assumed was the motor has gone, but now I'm experiencing a strange intermittent rubbing sound. It almost sounds like a leaf or debris rubbing between the tyre and mudguard, but it's happening too often to be a one off like that.

The rubbing seems to starts if I'm moving at high speed, but not when moving at a sedate pace. Sometimes a hefty bump in the road seems to trigger it, other times it just starts on its own accord. It's not disc rubbing, I'm certain of that. When it starts, it is constant, and doesn't go away when I'm coasting downhill, even at a slow speed. But it will go away if I come to a complete stop. If I stop jump off and spin the wheels at the side of the road, I can't reproduce the rubbing sound. Nor can I reproduce it in the bike stand. I'm completely baffled as to its origin. Any thoughts on what might do this? It went in with one problem, and seems to have come out with another, although I can't rule out my own handy work with the derailleur, but there's nothing to suggest it's the derailleur at all. Unless they did an extensive test ride on the bike, they may not have realised it came back with a problem, it's infuriating!
 
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fossyant

Ride It Like You Stole It!
Location
South Manchester
Welcome to the world of tracing noises. Check your QR's are tight on the wheels, check tyres aren't rubbing, and yes, it could be the discs/pads rubbing.
 
OP
confusedcyclist

confusedcyclist

Veteran
I'm not new to the strange world of curing rubbing, creaking and grinding, sadly, but this genuinely baffles me.

This bike has thru-axels, and there's no signs of tyre rubbing. Discs spin freely with no rub in the stand. Even when I apply the brakes just the pads contact the disc, discs are true as an arrow, so that cannot be the source.

What kind of rubbing stops when you stop a bike, but resumes once you pick up speed? :wacko: It feels much like mud guard rub, but as I mentioned above, there's no debris and tyres are not showing signs of abnormal wear.
 
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Foghat

Freight-train-groove-rider
If it happens when coasting as well as pedalling, then it won't be the motor, gears or pedals. To be doubly sure with the motor, presumably the sound persists when the motor is turned off?

This leaves the wheels. If you're sure the mudguards are not close enough to rub the tyres under any circumstances, it must be the hubs or disc brakes.

Given the work was done on the rear hub, you need to consider that. Maybe the mechanic didn't refit a seal/cover properly or rebuild the hub correctly.....although the intermittent nature in this case seems odd. Have you removed the rear wheel to inspect the hub and check for any obvious things like play in the bearings or an ill-fitting seal/cover?

To help rule out the brakes - have you tried applying the brake levers slightly when it's making the sound, to see if doing so changes the sound in any way. If there is a change in the sound, then the brakes are still a candidate for the source. Are the thru-axles tight? Are the caliper bolts tight?

Does the sound change or come and go when you shift your weight around on the bike?

If the front wheel fell over and hit the bike with enough force to bend the rear derailleur hanger, then the wheel may have suffered some damage too - so give the hub, rim, spokes and rotor a good inspection.
 
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confusedcyclist

confusedcyclist

Veteran
Thanks Foghat, that really helped me narrow my search.

I think I have worked out where the sound is coming from, I spun the rear up to high speed then swung the rear of the bike side to side and reproduced the sound. Its definitely coming from the hub or rear disc area, despite my earlier confidence that that wasnt the issue, I have a strong suspicion that the disc is bent from the fall in the boot, will confirm soon and report back!

I think the intermittently is a result of a very slight bend that reverberates at speed.
 
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confusedcyclist

confusedcyclist

Veteran
OK, I went back for a closer look. True to my prior experience, the rubbing sound is frustratingly unpredictable and still intermittent. I wasn't able to get it to happen again, no matter how fast I spun the peddles and jerked the frame about, as I was peddling by hand furiously and swinging the bike in the air, the postman walked by, he must think I'm a nutter. :laugh:

By the naked eye, I can't see the disc wobble at all, but when the wheel is rotating at speed and I gently apply the rear brake, there is obviously some slight bend as it will ping against the pad a little on each rotation, though this may not be outside the normal tolerance for trueness. It's only happening as the brakes are applied, maybe 50% or so. So that doesn't necessarily explain rubbing that occurs out on the road when brakes are not applied. Is it possible that the calliper is self-actuating, or getting stuck in a partially applied state? What might cause that? And why might it release again when I come to a stop?

I'm well aware I could well be barking up the wrong tree entirely.
 
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Foghat

Freight-train-groove-rider
The next things I would do to pin the sound down, in order, are:
  • Check the brake pads retract properly after the lever is released - you may have sticky pistons that need cleaning
  • Loosen the brake caliper bolts and try re-aligning in case the calipers are not straight in relation to the line of the rotor, then re-tighten - best done by viewing from both front/rear and above/below to check and ensure straightness
  • If you can get hold of one, try a different (and preferably known to be well-adjusted) rear wheel to test and see if the noise persists - you may need to transfer your rotor to ensure the right size
  • Ditto a different front wheel
  • If you can borrow a disc mount alignment/facing tool (such as the Park Tool DT-5.2), check and ensure the caliper mounts are properly square in relation to the thru-axle and rotor. You may need to get a suitably equipped shop to do this (note that not all bike shops have the necessary tool)
 
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confusedcyclist

confusedcyclist

Veteran
Sadly no spare wheels available to me, as it's my only 27.5" wheeled bike and no one I know locally has one, but I'll certainly work through the other suggestions, thanks again!
 

Ajax Bay

Veteran
Location
East Devon
no spare wheels available to me, as it's my only 27.5" wheeled bike
A 622 wheel with rotor, if necessary without a tyre on, would fit, I'd have thought.
 

silva

Well-Known Member
Location
Belgium
I hunted a noise for 6 months, and finally discovered the reason at nearly fatal time, a rim that was about to give up. Also 27.5" wheels, 62 mm wide tyres, pressurized to 3 bar. The outer wall was cracked throughout all spoke holes, the inner wall had a crack 10 cm long at one side, at the edge of sidewall-inner.
At that latter, the rim wall, depending on bikes load and tyre pressure, got pushed outwards, causing it to hit brake pad, and the tyre deformed different, causing it to touch things that it was clearly apart from when unloaded (alike bike upside down to check). Sometimes, without a clear reason, the noise disappeared for a month to then reappear for a month. Alike after an inner tyre replacement. Reason was the tyres pressure and/or the bikes load.
 
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