Another noisy disc brake thread

[glasgowcyclist]

After 10 months of silent operation from new, my Shimano M396 hydraulic discs began squealing like banshees. I cleaned the pads and discs with brake cleaner, which briefly alleviated the problem but it came back.

I bought new Shimano pads (F&R), cleaned the discs again and fitted them - bliss! I had silent brakes again.

Two weeks on and the noise has crept back and I'm at a loss to explain it; I'm very careful about keeping possible contaminants away from the brakes.
Brake performance is significantly down too.

Anybody had a similar problem?

GC

 

[Crackle]

Yes. I cleaned them, dishwashed them, bought different pads, still the same and finally bought Superstar resin pads and they are perfect now.

 

[glasgowcyclist]

Yes. I cleaned them, dishwashed them, bought different pads, still the same and finally bought Superstar resin pads and they are perfect now.

Thanks, I'll have a google for those. I'm still puzzled as to what brought it on after 10 months...

GC

 

[glasgowcyclist]

Hmm, this bit bothers me in the Superstar pads' description.. "the downside is greater noise and less ultimate power than soft pads".

GC

 

[Crackle]

Hmm, this bit bothers me in the Superstar pads' description.. "the downside is greater noise and less ultimate power than soft pads".

GC

All things are relative and they are not talking about squealing. Mine are squeal free. They probably mean a general rubbing noise and the soft ones don't last so long.

 

[Custom24]

This article might help. The part about the rotor turning into basically a violin bow makes sense to me, although I don't see why bedding in initially with heavy stops avoids it.

http://m.pinkbike.com/news/Tech-Tuesday-Silence-That-Squeaky-Disc-Brake-2011.html

I was also going to suggest anti squeal compound on the back of the pads. Apparently, though, if you want to try that route, then you need to buy cycling specific stuff, and not copper grease, for example.

 

[Yellow Saddle]

Disc brakes squeal because of pad material that transferred to the disc unevenly. Disc brakes work by one of two mechanisms - abrasive friction (resin pads) or adherent friction (metal pads). Both pads have to transfer material to the disc during bedding in. If the bedding in was not done properly, pad material wasn't transferred evenly they will be noisy and ineffective. If you swap pads from resin to metal or vice versa, the same happens and you have to remove all pad material and start again. The only way to remove pad material from the disc is mechanically i.e. elbow grease. Sand the disc with garnet paper until it has a satin criss-cross pattern. If your disc is shiny, it will squeal. If it is shiny in bits and pieces, it will squeal. If you have swapped pads without cleaning the disc off first, it will squeal.
Bedding in is kinda complicated. Follow the pad supplier's instructions. Very, very, very few mechanics understand the process.
Resin pads can be used on metal-compatible discs but not vice versa.
Resin pads work well and quietly at low brake temperatures whilst metal pads work better at high temperatures and are always noisier. However, there is no reason to live with the turkey gobble and wolf howl.

 

[glasgowcyclist]

This article might help. The part about the rotor turning into basically a violin bow makes sense to me, although I don't see why bedding in initially with heavy stops avoids it.

http://m.pinkbike.com/news/Tech-Tuesday-Silence-That-Squeaky-Disc-Brake-2011.html

I was also going to suggest anti squeal compound on the back of the pads. Apparently, though, if you want to try that route, then you need to buy cycling specific stuff, and not copper grease, for example.

The whole frame resonates once the brakes start to squeal, so that violin bow analogy is spot on.

I did remove the pads and lightly sanded them and the discs tonight but I can tell it hasn't worked. I'll get a proper go at it at the weekend. Thanks for the Pinkbike link.

GC

 

[Yellow Saddle]

This article might help. The part about the rotor turning into basically a violin bow makes sense to me, although I don't see why bedding in initially with heavy stops avoids it.

http://m.pinkbike.com/news/Tech-Tuesday-Silence-That-Squeaky-Disc-Brake-2011.html

I was also going to suggest anti squeal compound on the back of the pads. Apparently, though, if you want to try that route, then you need to buy cycling specific stuff, and not copper grease, for example.

That article has good info.

 

[Yellow Saddle]

The whole frame resonates once the brakes start to squeal, so that violin bow analogy is spot on.

I did remove the pads and lightly sanded them and the discs tonight but I can tell it hasn't worked. I'll get a proper go at it at the weekend. Thanks for the Pinkbike link.

GC

Sanding disc brakes is hard work. Light sanding doesn't work. You need sharp, fresh paper, preferably garnet paper, a good block and plenty of effort. There should be no shiny bits left and it should all be scratchy satiny. The latter is a formal technical term I've just invented.

 

[glasgowcyclist]

Sanding disc brakes is hard work. Light sanding doesn't work. You need sharp, fresh paper, preferably garnet paper, a good block and plenty of effort. There should be no shiny bits left and it should all be scratchy satiny. The latter is a formal technical term I've just invented.

I did as suggested and the noise disappeared for a week before returning. I guess I hadn't sanded them hard enough.
I had another go yesterday using lots of 240 grit paper until I reached that satiny finish and also sanded the pads but the noise is still there, albeit only at the tail end of braking, and the efficiency is still way down. I can't lock the back no matter how hard I try.

Do I need a coarser sandpaper?

Also, I had to sand the discs in situ because they are not removable and appear to be riveted on. I've never seen that before, is it normal?

GC

 

[Yellow Saddle]

I did as suggested and the noise disappeared for a week before returning. I guess I hadn't sanded them hard enough.
I had another go yesterday using lots of 240 grit paper until I reached that satiny finish and also sanded the pads but the noise is still there, albeit only at the tail end of braking, and the efficiency is still way down. I can't lock the back no matter how hard I try.

Do I need a coarser sandpaper?

Also, I had to sand the discs in situ because they are not removable and appear to be riveted on. I've never seen that before, is it normal?

GC

If you sanded the discs in situ i.e. still on the bike, you may not have done a thorough job. You need to access both sides of the disc and sand everywhere. The idea is to remove all the cementite (pad material) and create a slightly keyed but even surface for a new and even layer of cementite to form. After sanding you obviously have to break in the set-up again. This break-in is what helps to deposit an even layer.

Photos of the disc may help.

Did you fit new pads and do the break-in?
Have you fitted metal or resin pads?
Is the disc metal-compatible?

Some discs are riveted onto a spider, some are simply a single sheet of stainless steel with a built-in spider if you like. Yes, riveting is common and should not affect the process at all.

 

[glasgowcyclist]

If you sanded the discs in situ i.e. still on the bike, you may not have done a thorough job. You need to access both sides of the disc and sand everywhere. The idea is to remove all the cementite (pad material) and create a slightly keyed but even surface for a new and even layer of cementite to form. After sanding you obviously have to break in the set-up again. This break-in is what helps to deposit an even layer.

Photos of the disc may help.

Did you fit new pads and do the break-in?
Have you fitted metal or resin pads?
Is the disc metal-compatible?

Some discs are riveted onto a spider, some are simply a single sheet of stainless steel with a built-in spider if you like. Yes, riveting is common and should not affect the process at all.

Photos of the disc may help. I'll post some later this evening.

Did you fit new pads and do the break-in? Yes, when I first sanded them a couple of weeks ago. I haven't replaced them again. Did several hard stops from 15mph but noise was present from the beginning, albeit only as the bike came to a halt.

Have you fitted metal or resin pads? Resin

Is the disc metal-compatible? No. Warning on disc to only use resin pads.

I have hydraulic disc brakes on one of my other bikes (x-country full sus Trek) and never heard about this bedding-in process before. Those brakes are silent and very efficient.

Thanks.

GC

 

[Yellow Saddle]

Photos of the disc may help. I'll post some later this evening.

Did you fit new pads and do the break-in? Yes, when I first sanded them a couple of weeks ago. I haven't replaced them again. Did several hard stops from 15mph but noise was present from the beginning, albeit only as the bike came to a halt.

Have you fitted metal or resin pads? Resin

Is the disc metal-compatible? No. Warning on disc to only use resin pads.

I have hydraulic disc brakes on one of my other bikes (x-country full sus Trek) and never heard about this bedding-in process before. Those brakes are silent and very efficient.

Thanks.

GC

Your problem is almost certainly incorrect breaking in. "Several hard stops" is exactly what is not to be done. I've posted details of a proper break-in here before. I'll see if I can find any official Shimano literature on the topic.

 

[Yellow Saddle]

Here you go.

My guess is that the mistakes were:

1) Brake too hard too soon.
2) Came to a complete stop with the brake lever still applied.
3) Not enough gradual stops before braking hard.