Disc Brakes ineffective and noisy.

[Andy in Germany]

Elder Son is having Disc Brake issues. He rides a Canyon Neuro, and the rear brake has consistently been noisy, and ineffective:

He's cleaned the disc and replaced pads several times, but the problem always comes back, on occasion even though the bike wasn't ridden and just been stored for a a couple of days; if anything it seems to be worse if the bike isn't ridden: if he rides it frequently the problem returns more slowly.

He's replaced the rest of the system including the oil and the calipers.

Oddly, the only original part now is the disc, because everyone he asked claimed the problem "Couldn't" be the discs themselves.

Does anyone here have an idea what could be causing the problem? It would seem to be the discs, but it can't be dirt given that the brakes seem to deteriorate faster when left in a shed.

I've tried to take pictures but I'm not sure the details show:

 

[figbat]

Is that the right size disc for the caliper mount? It looks like the swept area is only 2/3 of the available area.

 

[chriswoody]

In general I haven't the foggiest I'm afraid, however, the first thing leaping out at me from your pictures is the wear marks on the disc itself. There seems to be a distinct line where the pads are only contacting the top part of the disc rotor, below this as well it is quite badly scratched. Are you sure that it's the right size disc?

Edit: Figbat types quicker than me, 😊 But basically what he said!

 

[bikingdad90]

Have the discs been recentred by backing off the screws and then braking and retightening or using a piece of business card either side?

 

[fossyant]

Check for a minor oil leak.

 

[chriswoody]

OK, having a quick squint at the Canyon Neuron on their website, it does state 180mm rotors, which you can see in the photos as well. So it seems that the rotors are definitely the right size, if I'm looking at the right bike.

There is still definitely something odd going on though, judging by those wear marks on the rotor and I would check that the pads are contacting the whole rotor and not just the top section.

 

[C R]

OK, having a quick squint at the Canyon Neuron on their website, it does state 180mm rotors, which you can see in the photos as well. So it seems that the rotors are definitely the right size, if I'm looking at the right bike.

There is still definitely something odd going on though, judging by those wear marks on the rotor and I would check that the pads are contacting the whole rotor and not just the top section.

Could it be wrong size adapter mount forthecaliper? The next size rotor would be 200 mm, so if the adapter was for a 200mm disc, it would move the caliper and the pads out by 10mm, which would explain the position of the pad marks.

Edited to add. Looking again, the pad marks seem to be out by less than 10mm, so my guess is probably wrong.

 

[chriswoody]

Could it be wrong size adapter mount forthecaliper? The next size rotor would be 200 mm, so if the adapter was for a 200mm disc, it would move the caliper and the pads out by 10mm, which would explain the position of the pad marks.

Edited to add. Looking again, the pad marks seem to be out by less than 10mm, so my guess is probably wrong.

It's not a bad assumption though. I recently changed some faulty SRAM calipers for Hope one's and the front wouldn't fit, it was too close to the adaptor and the pads weren't contacting the disc properly. I ended up spacing the caliper out to put it into the correct position relative to the disc. It is mentioned in the first post that the caliper itself has been changed, but we don't know if it was a like for like replacement.

Is the noise only when the brakes are applied, or all the time? If only when applied, then noisy discs can come about from contamination or not having bedded in the pads properly from new. I currently have a rear brake that squeals like a stuck pig when applied because I didn't have the time to bed them in properly before I used them, I decision I regret and a mistake I won't make again! If it's all the time, then possibly a pad is dragging on the disc and the caliper needs centering on the disc, as mentioned above. Release the mounting bolts on the caliper, squeeze the brake lever and with it still pulled in, re-tighten the caliper bolts.

Ineffective braking itself could be the result of the system needing a bleed. I've no experience of Shimano mineral oil systems, but with SRAM systems, after a bleed it's also advised to push some fluid back into the system at the end to re-pressurise the system or else the brakes will feel soft and ineffective. I don't know about Shimano systems though.

 

[Andy in Germany]

Thanks for all the thoughts. A couple of questions to clarify:

Have the discs been recentred by backing off the screws and then braking and retightening or using a piece of business card either side?

Have I understood this correctly, the procedure is to tighten the brakes with the piece of card on each side?

Check for a minor oil leak.

Would that account for the contamination? It's unlikely considering that Elder Son has changed the oil twice and the calipers are also new.

Is the noise only when the brakes are applied, or all the time? If only when applied, then noisy discs can come about from contamination or not having bedded in the pads properly from new. I currently have a rear brake that squeals like a stuck pig when applied because I didn't have the time to bed them in properly before I used them, I decision I regret and a mistake I won't make again! If it's all the time, then possibly a pad is dragging on the disc and the caliper needs centering on the disc, as mentioned above. Release the mounting bolts on the caliper, squeeze the brake lever and with it still pulled in, re-tighten the caliper bolts.

Contamination would seem unlikely given that Elder Son has cleaned the discs and the brakes and left the bike in the shed, then the brakes were already noisy and ineffective when he rode it two days later. In fact he reports that riding immediately seems to delay the onset of poor braking and noise.

Also remember he's replaced the pads, caliper and oil, cleaning the disc each time, which means he's centred the brake as part of that procedure. He's also successfully done the same procedure on dozens of bikes during his two year bike mechanics apprenticeship

Could you explain the process of "bedding in?"

I'll ask about the disc size and see what he thinks...

 

[chriswoody]

Could you explain the process of "bedding in?"

I'll ask about the disc size and see what he thinks...

Bedding in, removes the top surface of the new pads and primes them to work with the the rotors. It's a process that some will say doesn't really need doing, but all I can say anecdotally, is the only time I've had issues is when I've not done this.

For my calipers it's a case of get the bike up to a moderate speed on a flat surface and then pull the brake, not too hard and only to bring the bike back to walking speed, but not stopped. Repeat this 10 times, then ride the bike up to about 25 kph before pulling the brake hard, but again only down to walking speed, repeat this higher speed braking 10 times as well. Afterwards leave the brakes to cool down on their own before using them.

As mentioned above though, I do use brakes that have DOT5, I don't know for certain if mineral oil based brakes like Shimano also need to be bedded in this way, though I don't see why not.

 

[bikingdad90]

@Andy in Germany this is a really good video that explains the adjustment. It’s based on post mount but also applies to flat mount.

View: https://youtu.be/NmqGeLNcVIg

 

[chriswoody]

@Andy in Germany this is a really good video that explains the adjustment. It’s based on post mount but also applies to flat mount.

View: https://youtu.be/NmqGeLNcVIg

Unfortunately the video is for Cable operated discs, Andy"s son has Hydraulics which operate and adjust in a different way, I see there is a link in the video though to a video on Hydraulic adjustment.

 

[fossyant]

Check the hose is nipped up tight to the caliper - MrsF's leaked a little when not in use, enough to contaminate the pads - just a tiny bit from the hose joint, that's all it takes.

 

[Andy in Germany]

Check the hose is nipped up tight to the caliper - MrsF's leaked a little when not in use, enough to contaminate the pads - just a tiny bit from the hose joint, that's all it takes.

That would be consistent with the contamination being worse when the bikes is standing still; when the brakes are in use they'll be getting cleaned now and again.

 

[kingrollo]

Check the hose is nipped up tight to the caliper - MrsF's leaked a little when not in use, enough to contaminate the pads - just a tiny bit from the hose joint, that's all it takes.

Imo You're always up against up when someone starts saying "nipped".

"Just nipped it up a touch" - "Ive just nipped it up a touch - should be ok now"

Usually it's the prelude to needing a new and expensive part. !