Please help me solve this mystery

Notable hobbit

Just got a new (second hand) bike and the breaks are squealing (good price so can't complain). At the time I thought this would be an easy fix but having cleaned the rotors 4 times, replaced the pads (and bedded them in), straightened the rotors and aligned the callipers several times I can't get them to stop squealing and I'm out of ideas. Does anyone know of anything else I can do to stop them squealing.

What I don't understand is the brakes only squeal when going slowly. If I'm going quite fast they will slow me down really well then as I'm going about 5mph they squeal and I can't see why.
Thanks in advamce.

JGTR

You could try some copper slip on the back of the pads, sometimes they vibrate at low speeds, works in cars. Could also try adjusting the springs that hold the pads back depending on what brakes system you have.

cooldad

Brakes squeal sometimes. Stop faffing with them and just ride.

Notable hobbit

Thanks for the advice, I'll have to buy some copper slip.
I'd love to ignore it but it's very hard to enjoy riding/ride to work when every slow section or every set of lights you get an ear piercing howl.

Rigga

Sintered pads or organic?

Notable hobbit

Sintered

cooldad

Sticking grease on the back of the pads is more than likely to get on the pads. It's not a car. Sintered pads tend to be noisy. Get organic or kevlar.

LimitedGarry

Notable hobbit wrote:

Sintered

Well there's your problem right there.

Notable hobbit

I've just put copper slip on the backs of the pads and there is still no difference,
Ivr had sintered pads several times before with no such problems so I can't see why these would be any different,

The Rookie

It happens, if it's a fixed pitch squeal it's a resonance in the system, mounting stiffness, disc stiffness, QR tension etc etc all can be a factor or cause, sintered pads being stiffer than organic/Kevlar create less of a damping effect which is why it's always more likely with sintered. Avid CPS washers if you are using them seem to make it more likely as well.

Remove the copper slip before it contaminates your pads as noted above, really bad idea on bikes.

Notable hobbit

Just another update- I've rounded off the leading edge with sandpaper, cleaned the pistons, swapped the orbital washers around, bent the springs to make them more 'springy', put a washer between the callipers and the frame, refaced the callipers and in desperation taped a lead weight to the callipers (suggested on a us site).
Nothing has helped yet (lead weight removed since cause it's a stupid idea).

Notable hobbit

Also just noticed ( not sure if it helps) the pitch of the squeal gets lower the harder I pull the brakes

cooldad

99.98579898475% of all brake problems are caused by unecessary faffing. Actual proven fact.

Notable hobbit

The problems were there BEFORE I faffed so I very much doubt that's the cause

LimitedGarry

Notable hobbit wrote:

The problems were there BEFORE I faffed so I very much doubt that's the cause

He's pointing out the fact that the most obvious fix to your problem is getting organic or kevlar pads instead of sintered ones but you're still trying to fix the problem by doing everything else.

Dirtydog11

Was gonna suggest contamination but if that was the case they would squeel at all speeds and wouldn't slow you down particularly well.

Wooderson

It is all about stopping resonance. Given you've tried most things, the only other variable might be to try greasing the caliper bolt threads and re-torquing.

Notable hobbit

Another update, tried organic pads (no help) and have greased the calliper bolts. The vrakes only squeal at low speeds and putting water on them helps but does not cure the noise, i get a little judder when it squeals and also lose breaking power at the same time

LimitedGarry

Ok. Wow. If I was in your place, I'd be real pissed.

Has anyone suggested bent disc? Would explain the judder and why it only happens at slow speeds. My front brake squeals (quietly) but only at speeds above 25 km/h and when I pull hard (new pads).

Plodder82

FWIW,copper grease really does rot rubber brake seals,on my Defender (Landrover) and on my bike I use Silicon grease. Which is VERY good for rubber.
You can also look up "red rubber grease".

Plodder82

Also,organic pads are utter garbage sh*te,push iron,motorcycle or car.NOt worth a w*Nk!!

cooldad

May I suggest sir starts taking his medication again.

compuwiz_uk

LimitedGarry wrote:

Ok. Wow. If I was in your place, I'd be real pissed.

Has anyone suggested bent disc? Would explain the judder and why it only happens at slow speeds. My front brake squeals (quietly) but only at speeds above 25 km/h and when I pull hard (new pads).

i had brake judder on my brand new ( at the time ) cx bike

disk was true, & caliper looked properly aligned when looking from the top & the judder reduced as they got used BUT it turned out after they bed in some & needed adjusting ( manual adjust cable disks ) that although they were straight with the disk when you looked from above, they were slightly off when you looked at them from the edge & so were wearing the pads at an odd angle & thus got better as they wore in as they had better pad contact

sanded the pads flat again & re-aligned the caliper so it was square with the disk in both directions ( along the disk & up the disk ) & its been vibration free since, still howls nicely 1st use after riding through fog or drizzle though as it clears the water but soon shuts up ( a trait also common to my 29er, that thing sounds like a bus pulling up when i use it when its foggy )

only other time i have had noise/vibration issues on disk brakes is when i got muc-off bike spray ( that stuff with PTFE in it that makes the bike look shiney ) on the disks due to a well timed gust of wind ( was spraying the stuff onto a cloth away from the bike before using the cloth on the frame ), a little mist certainly went a god dammed long way that day, IPA & heat on the pads from a gas soldering iron wafting over them cured the disks & pads that day, more recently was when i spilled some tubeless sealant on the disk & just rinsed it off with tap water from the shower i was washing the wheel/tyre in at the time, stuck it on the bike & it screamed like a loon for the 1st few minutes of using the brakes, few good pulls from higher speeds soon cleared it though & it was back to normal service after that.