Squealing rear brake

ncn

I have recently fitted some Superstar Kevlar pads to my Shimano Deore M596 brakes and the fronts are fine.

The rear however are awful, when i brake they squeal like mad, I have tried the centering trick, loosen bolts, apply brake re tighten to no avail.

Anything else I can try?

Antm81

Sound like the pads and rotor are contaminated

cooldad

Do they work and squeal or not work and squeal?

ncn

Ah sorry the wife started whinging so I had to write quickly!

Yeah the brake works fine.

I have cleaned the disc with brake cleaner, so pretty confident it's not contaminated!

Also one pad seems to touch the disc before the other, even after centering, and it moves the disc a bit. So it causing resonance?

cooldad

Brakes can be noisy.
Softer pads (organic or kevlar instead of sintered) are quieter, other wise sometimes just riding them stops the noise.
If they work though, don't try anything drastic, like cleaning with odd things.
But if one pad is touching first the brakes aren't centred. Loosen the caliper, hold the brake on and tighten them up - the pads should touch at the same time, and not deflect the rotor.

The Rookie

Is it a high pitched squeal that is often more likely caused by some form of resonance, check all the bolts are tight but often the best way of changing the resonant frequency is by using a different type of pad.

ncn

cooldad wrote:

Loosen the caliper, hold the brake on and tighten them up - the pads should touch at the same time, and not deflect the rotor.

I have done this a couple of times^^^^

Also they are Kevlar pads and exactly the same set up on the front and the fronts have no squealing at all. I may have to investigate a bit more tomorrow before I go out. It's pretty annoying though haha!

The Rookie

If it's resonance, the system stiffness will be different at the front to rear.

So is it a high pitched squeal and only when breaking, possibly worse on light breaking than heavy braking?

ncn

Actually the opposite on light braking it's ok, just when you really jam them on, or just as you are coming to a stop.

Also it's more of a vibrating squeal as apposed to like on a car. I may have to try and video it haha!

The Rookie

That noise is symptomatic of a contamination, remove wheel, clean both sides of disc with IPAthoroughly and just wipe clean the surface of the pads, then refit.

ncn

Ok doke, I have some isopropyl in the garage so will set to work with that and see what happens!

Cheers

ncn

So took everything apart and cleaned it all up. Stuck it back together and it's still pretty much the same

I have however noticed that my piston looks to be weeping brake fluid when I squeeze the lever! Guess that's my problem....

poah

my superstar kevlar squeal but they work and the squeal disapears after a second or two. The uberbike kevlar didn't. putting it down to the fit/compound its no biggy.

Swap pads front and rear see if the front squeals

ncn

This is a constant really bad squeal, I swapped out the superstar for some stock shimano and they started doing the same almost straight away.

A quick google seems to show shimano can suffer with weeping seals, new caliper time it looks like.

parkinpants

you could just replace the seal kit, rather than getting a new caliper

ncn

There is no seal kit for this caliper unfortunately so it's new caliper time.

parkinpants

would a weeping seal not suggest it's losing fluid and therefore losing pressure? Therefore, if you're not losing pressure, might not be a weeping seal.

ncn

I think it is losing pressure, just been out to it and the first couple of pumps were really spongy. I'm just going to get a new caliper can't be bothered to mess about when I know it's dodgy.

The Rookie

Nothing you have said suggests you should no it is dodgy, if it's leaking it is obvious!

ncn

Sorry rookie, I think you are saying it's leaky so obviously change it?

The Rookie

No,, I'm saying that nothing you have said suggests it is leaking, if it's leaking it is obvious, if it isn't leaking don't change it!

ncn

Ah I have written I can see fluid weeping from the piston so the seal has definitely gone!

ryanincontrol

Had the same squealing problem with my xt m785.
Had it for a while before finding out the caliper is slowly leaking oil. It's only a tiny amount but enough to contaminate the pads.
Had replaced the caliper since, wiped the rotor and bought new pads. The problem is now gone.
I also reused the contaminated pads, the remedy was to burn them. Mine is organic and I left it infront of the cooker's blue fire for about 5 to 10 mins. Let it cool down then reuse.

Herdwick

Looks like you have found the problem with your brakes,
but almost every other time that there isn't a leak of brake fluid the reason pads are squealing is the friction between the piston caliper and the back of the brake pad when the brakes engage, I always apply a small quantity of copper grease on the piston caliper and the fit the brake pads, any annoying squealing then is gone, obviously take care not to contaminate the braking surface of the pad or you will run breakles

The same apply for cars and motorcycles, A good mechanic always has some copper grease on his bench....

The Rookie

Any grease like that is a bad idea.........

Not sure how a fraction of a second of movement causes a squeal!

Herdwick

not at all, squealing is caused between the friction of the back of the pad and the piston caliper when brakes are engaged or some times when slightly rubbing because the disc wants to drag the pad to the direction of turning and as it has no where to go it trembles under excessive force . any way I can't explain it in english but that's how it works, I do that on cars and motor bikes as well. no probs

Antm81

The front pads on my trance move, doesn't cause any squealing, just a clunk

The Rookie

Herdwick wrote:

not at all, squealing is caused between the friction of the back of the pad and the piston caliper when brakes are engaged or some times when slightly rubbing because the disc wants to drag the pad to the direction of turning and as it has no where to go it trembles under excessive force . any way I can't explain it in english but that's how it works, I do that on cars and motor bikes as well. no probs

Seeing as how the pad moves millimetres your theory is obviously very wron.

What grease does is act as an absorber. Car and bike brakes get hot enough to burn off contaminants, cycle brakes do not, which is why it's a very bad idea, a tiny bit of that grease in the friction material and you ruin the pad and can have no brakes.

Herdwick

All disc brake systems work the same way regardless of size, the squealing is a high frequency vibration.

http://www.aa1car.com/library/tr996.htm

The Rookie

Yes I know that, what has that got to do with greasing the pad, it's a bad idea on cycles as if the grease gets in the pad it's scrap.

Herdwick

copper grease won't get on the braking surface of the pad unless you put it there, the same way it never gets when I apply it to a car or a bike brake pad to silence the annoying brake noise. please read the link

eg When a door creaks you spray some wd40 or whatever lubricant to the hinges to shut them up, the same applies for the damn pads!!! carefully applying some copper grease on the BACK of the pads will help eliminate the squealing, copper grease wont melt but rather stick to the surface applied, and won't contaminate other critical parts.