XT M785 brake squeal

Paul Stumpy FSR

Hi,
i'm having trouble trying to diagnose my brake squeal from my XT M785's on my Trek Fuel EX9 2012. They are doing it something chronic and drive me mad. After a few heavy stops, they are fine, but a few minutes later, they're at it again. Is really :oops:
I've cleaned the rotors with disc brake cleaner and also changed the pads from the resin ones to the metal ones, but still doing it.
I've had a good look at the crimp connector on the caliper and the pistons and cant see any sign of a fluid leak.
Does anyone have any pointers?
thanks
Paul

The Rookie

Oh dear, what disc brake cleaner?

Also what nature of squeal, is it a constant frequency but changing volume, or changing frequency, they have different causes.

Paul Stumpy FSR

Hi,
i'd say its a constant high pitched squeal that doesnt go away, only after a few heavy stops.
i used the bikehut (halfords) citrus disc brake cleaner.
thanks

The Rookie

Is that a bike or motorbike cleaner? Most disc cleaners are no good on bikes as the pads don't get hot enough to burn off contaminants, which is why rubbing alcohol (IPA) is recommended.

A contestant pitch is a resonance and not due to contamination, check all the mounting bolts for disc and calliper are tight, but sometimes you just have to live with it or change a part to something stiffer, it is worst with metal pads.

Paul Stumpy FSR

its bike cleaner.
i've take the caliper off the post mount, cleaned all the crud out and re aligned it all now so we'll see. not sure how it can be a resonance if it stops after a few heavy stops?
i'd say it probably is a tad worse with the metal pads. whats funny though is when i was bedding them in there was no noise at all, but the further into the ride i got, the noise returned!
think i'll give the rotor a proper clean with some other stuff.
cheers

Antm81

I may be being stupid but are you sure it's not water, general trail crud as you're riding, then burning off a once the brakes are used?

stubs

Sometimes these are the only cure I am afraid

Paul Stumpy FSR

Antm81 wrote:

I may be being stupid but are you sure it's not water, general trail crud as you're riding, then burning off a once the brakes are used?

maybe i did think that, but they've never been anywhere near this before. always been razor sharp whatever the conditions. perhaps a slight chirp on first application, but now its constantly until i've stopped. my mates ones you dont hear anything from, they are SLX and Elixr 3's.
think i'm just going to have to adopt the earplug method above and suck it up :evil:

ryanincontrol

Paul Stumpy FSR wrote:

Hi,
i'd say its a constant high pitched squeal that doesnt go away, only after a few heavy stops.
i used the bikehut (halfords) citrus disc brake cleaner.
thanks

Had the same problem with my M785's
I found there is a tiny leak coming out of one of the pistons. Not enough to make a mess that you would suspect but enough to contaminate the pads. After a few heavy stops the squealing goes away I presume due to it being burnt away.
If you have weak braking power then it's likely you have the same problem as I had.
Check your pads for contamination. If it's mineral oil it will burn off.
With mine, I put the pads directly infront of a gas stove fire for about 5 mins. I know people don't advise burning organic pads but what is there to lose if it's going in the bin anyway. My organic pads were fine after that and was pleasantly surprised with how much stopping power it has without contamination.

swod1

hmm, does anyone know what type pads come supplied with new m785 xt brakes bought from crc?

I've a similar problem with mine but this is when the brakes get wet there is noise which does go after repeated braking but in the dry the brakes are quiet and they are bedded in, I've learnt from that mistake before.

I think the pads are sintered from what I can gather, never tried organic pads do these make noise if water gets on the pads too?

Paul Stumpy FSR - give the discs a real good clean with isopropyl alcohol, you could try a small piece of paper towel in between the pad, the piston and you will know if there is a oil leak after pressing it a few times with the wheel in etc.

Paul Stumpy FSR

swod1 wrote:

I've a similar problem with mine but this is when the brakes get wet there is noise which does go after repeated braking but in the dry the brakes are quiet and they are bedded in, I've learnt from that mistake before.

exactly the same with mine
i've never had a problem in the dry too, only in these wintery months.
will have a look at that. I like the idea of a paper towel behind the pad. may have to give that a try.
My original pads were the resin ones, but have now changed to the metal ones. Hopefully they aren't leaking as that would be a pain.
I've cleaned the rotors with white spirit now. But I've also managed to put a slight kink in my rotor too which you can feel through the lever. i'm hoping to sort out.
cheers guys

The Rookie

White spirit leaves a residue, alcohol is better.

swod1

Paul Stumpy FSR wrote:

exactly the same with mine
i've never had a problem in the dry too, only in these wintery months.
will have a look at that. I like the idea of a paper towel behind the pad. may have to give that a try.
My original pads were the resin ones, but have now changed to the metal ones. Hopefully they aren't leaking as that would be a pain.
I've cleaned the rotors with white spirit now. But I've also managed to put a slight kink in my rotor too which you can feel through the lever. i'm hoping to sort out.
cheers guys

If they were leaking oil you would get the squeal noise constantly even in the dry and you would see traces of oil around the disc rotor.

I think its just the time of year as riding in the mud and grit isn't going to be good for brake pads anyway unless you use sintered metal pads which are more durable.

Paul Stumpy FSR

i've just changed to the sintered metal pads and its now really, really loud!
I must admit, i have seen no evidence on the backs of the pads or inside the caliper of oil leaks.
pesky things...

The Rookie

swod1 wrote:

If they were leaking oil you would get the squeal noise constantly even in the dry and you would see traces of oil around the disc rotor.

I think its just the time of year as riding in the mud and grit isn't going to be good for brake pads anyway unless you use sintered metal pads which are more durable.

If the pads get contaminated they make make a noise, not really a squeal, or they may just as well make no noise at all, your seeping statement simply isn't true I'm afraid.