Discussion
Hi, I've had my bike for about 3 years and I've had no issues with brake squeal but lately I can't get rid of it. I've been tearing my hair out with it, so I bought 2 new sets of pads, lightly sanded the discs down then cleaned them and the calipers with muc off disc brake cleaner. I installed the new pads without touching surface then bedded them in properly. The brakes were sweet again, silent with full stopping power.
I then went out for a ride got to the bottom of the first decent hill and sure enough the squeal starts again from both discs!! The brakes are shimano deore M615's. Does anyone have any idea what the issue might be? Could the discs need changing, I've inspected them but there is no 'lip' around the edge or could the caliper be weeping fluid from inside?
Any ideas appreciated
I then went out for a ride got to the bottom of the first decent hill and sure enough the squeal starts again from both discs!! The brakes are shimano deore M615's. Does anyone have any idea what the issue might be? Could the discs need changing, I've inspected them but there is no 'lip' around the edge or could the caliper be weeping fluid from inside?
Any ideas appreciated
I'm new to disc brakes on a bike, however I've been driving/riding and maintaining vehicles with them for over 35 years.
Squeal is the audible output of mechanical vibrations in the braking system, normally the pads vibrating against the disc and caliper.
You have already tried to make sure there is no change in braking friction on different sections of the disc so look at the following.
The leaf springs around the pads are threre not only to hold the pads in place, but to damp out vibrations so it is worth checking they are seated/fiited properly and are not worn.
In car and bike applications you sometimes need to apply some anti-seize compound, coppaslip is the old traditional choice, but there are more modern ceramic compounds too. This prevents friction between the pads and pistons, but you need to be very careful not to get any on the front of the pads so I'm not sure this is a good idea on push bike brakes due to the size.
It is possible that the ends of the pistons are no longer perpendicular to the sides, this will allow movement, i.e vibration, in the pads.
Similarly if the pistons or caliper bores are worn this will allow movement and vibration.
Have you checked the runout on the discs? By this I mean do the discs wobble as you spin the wheels. Best done with a dial gauge, however if you can cobble together a way to hold a pencil point on the disc that may work or simply look carefully at the disc position in the caliper as you rotate the wheel.
All a bit general I'm afraid, hopefullty someone with specific cycle disc brake experience may be able to help more.
Squeal is the audible output of mechanical vibrations in the braking system, normally the pads vibrating against the disc and caliper.
You have already tried to make sure there is no change in braking friction on different sections of the disc so look at the following.
The leaf springs around the pads are threre not only to hold the pads in place, but to damp out vibrations so it is worth checking they are seated/fiited properly and are not worn.
In car and bike applications you sometimes need to apply some anti-seize compound, coppaslip is the old traditional choice, but there are more modern ceramic compounds too. This prevents friction between the pads and pistons, but you need to be very careful not to get any on the front of the pads so I'm not sure this is a good idea on push bike brakes due to the size.
It is possible that the ends of the pistons are no longer perpendicular to the sides, this will allow movement, i.e vibration, in the pads.
Similarly if the pistons or caliper bores are worn this will allow movement and vibration.
Have you checked the runout on the discs? By this I mean do the discs wobble as you spin the wheels. Best done with a dial gauge, however if you can cobble together a way to hold a pencil point on the disc that may work or simply look carefully at the disc position in the caliper as you rotate the wheel.
All a bit general I'm afraid, hopefullty someone with specific cycle disc brake experience may be able to help more.
Piginapoke said:
Likely faulty seal letting hydraulic fluid past piston onto disc
This is what I'm starting to suspect, the squeal just gets worse and worse and then the brakes start to fade with use. Suppose i'll have to pull out more money, wouldn't care I've just replaced the full drivetrain and bought new tyres etc. There was me thinking Shimano stuff was indestructible 
youngricharduk said:
This is what I'm starting to suspect, the squeal just gets worse and worse and then the brakes start to fade with use. Suppose i'll have to pull out more money, wouldn't care I've just replaced the full drivetrain and bought new tyres etc. There was me thinking Shimano stuff was indestructible
Not sure this is your issue.If fluid got onto the disc, you would have ZERO braking effort.
Do you put your bike on a boot rack to go places? If so that’s a good cause of brake problems particularly dirty diesels exhausts they are great at contaminating discs.
You only need a bit of chain lube (why I dispare at people who spray GT85 etc on their cassettes) or similar to contaminate a disc to cause squeals and crap performance or a bit of air in a calliper. I suspect about 70% of riders are running round with contaminated pads and discs or bad bleeds as so many say had a go on <a friends bike> and his other make brakes were amazing or they whinge at lack of power on brakes I know are really powerful.
I just sold a bike with basic deores but with 203mm rotors and sintered pads, levers set for one finger use. The guy test riding it almost took his nuts out on the stem bringing it to a stop, said he’d never used brakes as powerful.. They were just clean and well bled.
Deores did used to have a reputation for leaking calipers so if you have been fastidious and know you’ve not contaminated them and the bleed is or was good it is likely the seals have gone, still £24 for a whole deore brake on CRC at the minute.
You only need a bit of chain lube (why I dispare at people who spray GT85 etc on their cassettes) or similar to contaminate a disc to cause squeals and crap performance or a bit of air in a calliper. I suspect about 70% of riders are running round with contaminated pads and discs or bad bleeds as so many say had a go on <a friends bike> and his other make brakes were amazing or they whinge at lack of power on brakes I know are really powerful.
I just sold a bike with basic deores but with 203mm rotors and sintered pads, levers set for one finger use. The guy test riding it almost took his nuts out on the stem bringing it to a stop, said he’d never used brakes as powerful.. They were just clean and well bled.
Deores did used to have a reputation for leaking calipers so if you have been fastidious and know you’ve not contaminated them and the bleed is or was good it is likely the seals have gone, still £24 for a whole deore brake on CRC at the minute.
youngricharduk said:
Gary29 said:
Not sure this is your issue.
If fluid got onto the disc, you would have ZERO braking effort.
True, I also haven't lost any noticeable pressure in the lever, but what if it was a minuscule amount? Just enough to contaminate the pad?If fluid got onto the disc, you would have ZERO braking effort.
I have had several leaks of various causes recently.
If you are just getting a really small amount of fluid leakage then you can get a lot of squealing with some reasonable braking initially with it getting worse the more you are braking...often dropping to almost no braking by the time you have stopped. In one case my braking was actually BETTER in the wet!
My issues were leaking seals, leaking bleed valve and contaminated pads/disc. Not all at the same time I must add!
greenamex2 said:
youngricharduk said:
Gary29 said:
Not sure this is your issue.
If fluid got onto the disc, you would have ZERO braking effort.
True, I also haven't lost any noticeable pressure in the lever, but what if it was a minuscule amount? Just enough to contaminate the pad?If fluid got onto the disc, you would have ZERO braking effort.
I have had several leaks of various causes recently.
If you are just getting a really small amount of fluid leakage then you can get a lot of squealing with some reasonable braking initially with it getting worse the more you are braking...often dropping to almost no braking by the time you have stopped. In one case my braking was actually BETTER in the wet!
My issues were leaking seals, leaking bleed valve and contaminated pads/disc. Not all at the same time I must add!
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