Or have I?

New pads swapped disc front to back (front still squeals, rear still doesnt) lubed pistons… What else could it be?

Brake is working well btw – Shimano XT M785

Cleaned discs, checked alignment, copper grease on back of pads?

Yes, yes and no. Will see if I have any copper grease

Tested for leaky piston seals by placing a piece of tissue between the pistons & pads, clamp the lever in and check in the morning?

I saw this recommended on here the other day & need to test mine. Should show up any small leak that would then contaminate the pads.

copper grease on back of pads?

Don’t do this.

Sounds like it could be the shimano issue of the seals letting by a tiny amount of fluid, contaminating disc and pads.
If so, the only fix is to replace the caliper.

Don’t do this.

Have never done this and always thought it sounded like a bad idea anyway, but curious, why do you suggest not doing it? I just assumed there was potential for contamination of the pads…

Ta

It’s an old wives tail.

Heat

Copper slip

The carrier grease melts out of it onto your disks and pads.

Car brakes mask contamination alot better bike brakes do not.

Ok cheers all such a ball ache I might just buy a new brake.

If brakes both work well and the squeal didn’t move from front to rear with the pad swap, then it doesn’t sound like a leak/contamination. Had the brake mount faced?

My guess is a ‘lazy piston’. One side if effecting less force on the disc. I would check to see if the disc is deflecting slighlty when the lever is squeezed.

Have you tried bleeding the system? Most of my squealy brake problems seem to relate to a small amount of air getting in when changing pads. My brakes are quite old (Hayes stroker gram) and after removing the old pads I usually try to push the drums out a bit and apply some dot 4 to keep things working, which is the point at which some air might be getting in. It’s an easy job to fix though.

Again, curious, why do you think air in the system results in squealing?

I’ve had this with the same brake set and was all but ready to chuck them. Check the hose to caliper connection is definitely tight.
Clean again, including some metho on a string around the piston. Clean the discs really well.
It finally worked for me!

Did the problem continue immediately after swapping discs and pads? Or only after a bit? Did you use the new pads on the old disc at all? Is there a loss of power with the squealing?

I’d recommend the tissue in brakes overnight suggestion above to find out if they’re leaking.

Are we talking a mildly annoying noise that goes away with firm braking, or an horrific unstoppable squeal whenever you use them?

I was going to suggest rim brakes, assuming this was a road bike question.

But I see you’ve got Shimano XT-M785. I solved this exact same problem by purchasing some Hope brakes. They still squeal if they get really wet but I think that’s inevitable.

What pads are you using?

Assuming no leak I’ve always found that the type of pad you use has the biggest effect. Best option for me with good performance, durability and quiet operation is Uber Bike Race Matrix pads.

I have used coppaslip without getting contamination. the point is you use a tiny tiny bit

So much that it’s completely pointless.

It dries out and causes gumming more than it prevents squeeling.

But what ever placebo you believe in from the 1970s. Most if not all (I’ve not checked alllll but I’ve consulted the paperwork for those that I use regularly ) manufacturers warn against this practice.

I don’t do it regularly. I have done it once but it caused no issues.

Try loosening the caliper mounting bolts; does that cure it? If so, it’s an alignment problem

What discs are you using? Really lightweight flimsy things with funny wavey designs?

Squealing straight away after swapping pads and disc. (Brand new EBC pads and a disc swapped front to back) No time for it to get contaminated.

Squealing loudly as soon as the brake is anywhere near on!

check to see if there is any leakage on pads or around caliper. check the disc for signs of contamination too. Got one Zee caliper leaking from the hose join.

Pad spreader spring not seated correctly or bent out of shape during installation?

Over-exuberant use of WD-40 / GT85 etc elsewhere on the bike (e.g. chain) causing overspray contamination?

New bike time.

WD40 fixes every squeal I’ve had, worth a go I guess?

Been through this 2x so far now on 3rd event so on the basis that there is a permanent irreparable leak in/around the caliper what non Shimano brakes that won’t brake the bank hopefully in stock somewhere thanks

@jag61

Been through this 2x so far now on 3rd event so on the basis that there is a permanent irreparable leak in/around the caliper what non Shimano brakes that won’t brake the bank hopefully in stock somewhere thanks

Everyone has their favourite brakes I guess. Got Sram Code R’s on both bikes –
All relatively cheap on eBay that had been taken off new bikes to be replaced with Hope bling. Love them – never any issues – hardly ever need bleeding – relentlessly powerful. Brand new from CRC they’re £110 an end though so possibly not cheap.

Guide RE are nearly as powerful but a less nice lever and no bleeding edge port on the caliper so slightly fiddlier to bleed.

Guide RS are less powerf than both the above but have a nice feeling lever and they’re still 4 pots so pretty decent.

Other make wise Hope E4 generally get positive comments about reliability but perhaps lack a bit of initiative bite – plus ££££.

THERE IS NOTHING WRONG WITH YOUR BRAKES.

Brakes sometimes squeal (I work in brake design for a car manufacturer)…

…and sometimes even one hundred Engineers with access to all the production tools and Computer Aided Engineering can not change the calipers, pads or discs in a way that fixes the problem.

Your cheapest and easiest solution is to try some pads from a different manufacturer or made from a different friction material.

It happens on PORSCHE too :o)

Resin pads in that brake I found to
Be squeak free.