Disc Brake Squeal

[concussion]

Hi folks, does anyone have suggestions for getting rid of disc brake squeal? I've tried everything I can think of: IPA, sanding, automotive brake cleaner, new pads, new rotors and nothing works for long. The noise is awful but I'm suffering a loss of power too. I'm on the road almost exclusively, is there a chance I'm picking up contaminants?

[Psycholist]

Are you running a Hope disk? The squeal is a feature of some of them.

Check the alignment of the caliper with the disk.
Check for strange wear patterns in the pads/disk.
The disk should be no less than 1.5 mm thick at it's thinnest.
Try putting copper grease on the back of the brake pads.
Try running the disk without the spring that pushes the pads apart in case this is rubbing or misaligning the pads.
Try different pads - I'm a big fan of Superstar's cheapest resin pads, they're surprisingly quiet even in wet conditions and they bite and hold better in the wet than the much more expensive kevlar compound they say is their best. If you're running metal pads try organic/resin if running resin try the opposite.
Check where you're storing/parking the bike - do other bikes/oily things get rubbed against the disk while it's left there? The loss of power is a dead giveaway that the disk is getting contaminated though. Any oily puddles on your spins?

Based on the very brown colour of my commuter bike chain I reckon I pick up more than enough contaminants from the road, but the Magura Louise I run up front has been flawless for years. When it hits 200ish degrees at the bottom of the large hill from the house in Cork there's a bit of howling, but I'll allow that...

[seanryan]

Are they fluid or mechanical disk brakes?
Could a leaking piston be the problem? Would explain why the noise eventually returns, and the loss of power.

[Psycholist]

Good point - some of the Shimano 2 piston disks (M765 era Shimano XTs and everything else with that style caliper) did leak really slowly onto the disk. Replacing the caliper was the only solution that worked in this case. Luckily there's http://bicikli.de/shop/SHIMANO-spare-parts - unluckily, the caliper is not available from Shimano as a spare part, so it'll have to be off ebay or similar .

[concussion]

Thanks for all the suggestions, looks like I have some investigating to do. Brakes are Shimano LX M585 with Shimano bog standard rotors and resin pads, can't remember the brand.

The calipers are about 8 years old so if leakage was an issue with this design then it's quite possible this could be the problem. One of the pistons on the rear is sticking and causing a lot of resonance when fully applied but it wasn't an issue when the front brake was working properly. I replaced rotors and pads a few months ago but since then it's barely left the shed so I was quite surprised that the front was losing power. It's quite possible that spraypaint was used in there so that might be an issue too.

I'll remove the springs and see if this makes any difference before I start ordering new parts. How does copper grease help when applied to the back of the pads? The interim solution is to rub mud onto the rotor, I get about 15 minutes of good power that way

[Psycholist]

If rubbing mud into the rotor fixes it then the disk is definitely contaminated. Take the disk off and give it a really good wash using washing up liquid, then follow this with a wet sanding with clean emery paper (Leaving a bit of washing up liquid on it is no harm for this either) and another very good wash. If you see water beading up on any parts of the disk rather than coating the disk surface with an even layer of water then it's still contaminated.

As for the pads, try cooking them at max temperature in the oven or on your cooker hob or better again on a hot plate in a fume hood until you no longer see smoke off them - this will smell bad and the fumes are most likely not totally safe to breathe, so if you have a blow-torch or a hot air gun it's better to use this outside rather than doing it in the kitchen...

Cooking the pads does reduce their remaining life, but it's better than throwing them in the bin.

[Psycholist]

To diagnose the possible slow leak in the caliper get everything in the caliper clean(ish) and dry, clamp a bit of kitchen paper between the brake pad and the piston on each side of the caliper and use a cable tie to hold the brake lever pulled in. Leave it like this for a few days - if the paper gets wet the caliper is leaking.

The copper grease sticks the pads to the pistons slightly and in doing so changes the resonant frequency of the assembly, so if the brake howl was a result of vibration at resonant frequency in the system then the grease would change it. I use this (sparingly - copper grease and ABS sensors don't get on too well apparently) on the car when changing brake pads, but have never needed it on my bike. I did find organic pads eliminated the brake howl I got from metallic pads on my Giant Trance in the Alps.

[concussion]

Thanks for the suggestions, great advice as ever!

Seeing as I haven't been on this forum in an age I skipped back through the years last night....there's some good stuff lurking in there. Good memories!

[concussion]

I was fully planning on trying to fix my brakes over the weekend but never got the chance. This is good as today I have far more movement in my front lever than before so I reckon it's time for a replacement! Think I'm going to swap out the M585 calipers with some M615's and keep my current levers - should be a (reasonably) inexpensive fix.

[Joejoebeans]

The enduro solution is to throw out the whole bike and buy a new one. If it's older than 6 months it's no longer enduro

[seanryan]

Are the brakes 12 speed metric? If not they're not worth repairing...


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[concussion]

12 speed metric? Only the best anodised drillium doo-wangles for me


They were M585's , now they're M585 levers with M615 calipers. Just have to rewash the rotors to ensure they're clean and bleed the lines and I should be done.

I do rather like the enduro approach, wish my wallet was in agreement!

[seanryan]

Yeah sram have released eagle which is its new 1x12 drivetrain, and now trying to introduce metric shock sizing which means in ~5 years all the current frame and shock sizings won't be compatible with the shocks being sold by them, so either you'll have to live with a 5+ year old frame and shock with God knows how many miles, or pay for a brand new frame with shock that cannot be interchanged with older models.


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[Psycholist]

Or man up and use a hardtail ... That's my method for getting decent life from my full suspension bikes anyway. The downside is that since nobody seems to be making reliable suspension forks either I'm chewing through a fork every 2 years or so...

It's already at the point that unless the frame is very special indeed (Or basically new) that it's often a better financial decision to buy a second hand frame with shock than to buy a new shock to keep an old frame going.

Even buying suspension forks these days is a nightmare. It used to just be a matter of matching the suspension travel and fork strength with your frame and the use required, now there are 3 steerer tube standards (Though thankfully 1.5 only shows up on seriously heavy duty stuff (And the odd Cannondale ) but frustratingly 1-1/8", the main standard since the '80s, has been all but killed off except for low end forks. Then there are 3 front axle standards (Though 20 mm and QR are getting rarer) and 3 wheel sizes, with 26" wheels dying off here, even though they've been standard since the first MTBs were mass produced (the very first Tom Ritchey welded MTBs were 650B though - nobody was calling them 27.5" yet, closer to 27" anyway).

Throw in all the headset options (External/the random internal standards and the three steerer sizes), press fit BB options (There are at least 2 'standard' frame diameters for this, this is still better than snap happy square taper BBs and guessing what length you needed so the cranks cleared the frame back in the day), the 27.5+ and fatbike wheel/tyre standards, the boost BB offset thingum and E13 and SRAM's new hub drivers, it's like the Cambrian explosion in MTB at the moment ...

The really bizarre thing is the idiotic 100ish year old standard for pedal threads, the most glaringly poor interface between parts on a bike, hasn't been touched at all - the pedal axles should be part of the cranks like was done with the BB axle years ago, then you pick the pedal style and bearings you like and bolt them to the pedal axle, much simpler and the load is carried on an interface that the crank manufacturer can control properly rather than an interface guaranteed to degrade over the normal life of the parts no matter how carefully it's made unless it's all done in steel like it was 100 years ago...

It's going to be a total nightmare in a few years time for people like me who want to keep their 26" bikes running to find parts that fit, not to mind parts worth fitting ... Though at the moment I have at least one 16, 20, 24, 26, 700C and 27.5" wheel in the garage - but no 29ers... That's where I draw the line ... Admittedly 700C is about the same as a 29er rim, but they're for road bikes... Are these my feet?

[concussion]

And I thought I had it bad trying to source 8 speed components for my last upgrade. I thought cycling was supposed to be easy!

New calipers have been fitted...is it normal for some drops of fluid to come out at the pistons when I'm bleeding them??

[Psycholist]

Definitely not. All the fluid should stay inside in all conditions - hopefully there was just a bit on the surface either from the bleed port or the brake line connection that you didn't notice till afterwards. I'd wipe it dry and leave it overnight with the lever pulled and look for more leaking in the morning.

[Joejoebeans]

Or man up and use a hardtail ...

I'm quite sure you were out on the squishy bike yourself this weekend. You must be getting soft in your old age Cormac

[seanryan]

Yeah Cormac I've actually forgotten about half of those there are more and more popping up every day!
Took me 6 months to find the revelation that i had on the Meta 55, everything was either tapered or not long enough or not the right axle type. But thats marketing, create the demand..

[Psycholist]

I was on the full susser because the hardtail fork bushings were falling apart. Hence the fork I bought in the car park ... The Anthem is lighter, faster and more efficient and comfortable than my hardtail, but I wouldn't give it more than 6 months before the frame breaks again if I used it for as many spins as I use the hardtail for. The anthem is kept for all day spins in dry weather and setting quick Ballyhoura loop times...

[Rock Souled]

I've run into a similar issue here with contaminated pads. 2nd or 3rd time in as many years. Replaced the brake the last time. I've decided to just buy a blowtorch. €70 for a kit in B&Q. If anyone else is in need of torching a set of pads, let me know and I'll give them a loan.
[edit]
I did look into the possibility of cooking the pads... but I was met with a deathglare so strong I'm concerned about my mother's health.

[rdhma]

I did bake pads before. It worked, but the kitchen smelled ...not so good... afterwards.

[Psycholist]

I picked up a blow torch type thingie from Lidl a couple of weeks back too. It's supposed to be for burning weeds and lighting the BBQ, but it'll do brake bads too... Also Irish weeds are too full of water to burn quickly or easily even under a propane-butane flame.

[concussion]

So....does the blowtorch do the job with the pads?? I replaced my levers, scrubbed down the rotors with ample amounts of brake cleaner and put on new pads. Result - the rear brake is perfect after three days, the front started screaming after a 15 min commute. This is probably the third time I've had to replace pads and wash rotors in the last year, to say this is vexing is an understatement. I may also have access to a furnace with and extractor at work - any ideas of temperatures and times for baking?

[Psycholist]

The blowtorch does a reasonable job on pads for me for XC/commuting use. It isn't good enough to get my trials bike disks back 100% but they're usable but slightly noisier and down on bite and hold, so there is a drop in performance as soon as contamination is involved. As for baking them, I've given mine about 200 degC in the oven and it has helped bring oil to the pad surface, but won't burn it off.

There is also the option of using something that reacts with oil like oven cleaner/caustic soda to chemically break it down - it should make the oil into some sort of soap, which can then be washed off, but I haven't tried this (Not sure whether it works for all hydrocarbons). I already keep oven cleaner around for removing the anodising from aluminium...

Since the disks are getting contaminated repeatedly, either you're hitting lots of oily puddles on the way to work, something oily is rubbing off the disk while it's parked at home or work or the brake is leaking very slightly. I've not had problems with oil on the road even on the section of the white Ballyhoura loop where they appear to have buried a few cans of oil in the ditch, so there's oil oozing across the trail all the time, mixing into the puddles, so it comes down to where the bike is stored and whether the brake is leaking.

[concussion]

I found a torch at work and gave them a blast - the power came back but there was still noise. Much heavy braking on the way home led to almost silent braking and enough power to for stoppies again

There's noise in the back brake but it's resonance so I'll check alignment. If that doesn't work I'll remove the spring or try some copper grease.

I'm at a total loss to explain this, it hasn't been raining so no road contamination. The bike is stored in a draughty shed which does contain paint etc but nothing is rubbing against it.

There's a big thread on MTBR about this, lots of complaints about phontom brake failures. If it takes a blast with a torch every few weeks I'll live with that...I just hope it's still good in the morning.

On the plus side, I'll be taking Emilia up to Ballyhoura on her balance bike soon....though she may need some help climbing the fireroads!

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