My commuting bike has Shimano Deore M615 brakes. The front is good as gold. The rear screams like a banshee at the slightest touch of the lever. It’s so loud that every pedestrian, driver and dog in 100 metres stops and stares at me. I’ve got to the point where I avoid using it as much as possible.

I’ve tried new pads and discs (shimano disc, uber and shimano sintered pads). Stripped all the mounts and cleaned everything. Tried a smear of silicon grease on the back of the pad. Spent ages fiddling with the caliper alighnment. Nothing has come close to working. I was a bike mechanic for 8 years. IT CANNOT BE THIS HARD!!

Is there anything else I can try before I buy a new brake?

Sounds like the caliper is probably leaking for it to persist despite everything you’ve done? Probably a replacement.

No signs of leaks anywhere, pressure is good. Other than the noise it works perfectly. Driving me mad!

Caliper is leaking, it’s a known Shimano problem.

If you can’t see any oil you’re not looking hard enough.

https://www.chainreactioncycles.com/mobile/shimano-deore-m615-disc-brake/rp-prod208317?gs=1&sku=sku848100&utm_source=google&utm_term=&utm_campaign=&utm_medium=base&gclid=CjwKCAjw3MSHBhB3EiwAxcaEu3Aqw1szQDAeLpzleUhBriZ_N-iT1AQ0HdrO05MhPD-soFJbB7-fJRoCczkQAvD_BwE&gclsrc=aw.ds

£25 and you can probably sell the lever on?

Thanks @blitz
Dubious it’s a leaking caliper. Seen these before, and I wouldn’t expect it to make any diffence on a brand new set of pads and disc, straight away. The noise was there after the first squeeze of the lever. But for £25 it’s worth a shot.

You say the brake is on a commuter- Is it perhaps the case the pads haven’t bedded in properly? I had squeaking brakes when I put new pads and rotors on and then only used them on flat trails. Thus glazing up the pads so to speak. Took the bike out on some steep muddy routes and the squeaking stopped. Lather up the disc with mud and grit and do some aggressive stops. This might work.

Yes, I would try sanding the rotor and pads and bedding it in properly first. I had a similar thing with a spare commuter bike that hadn’t been ridden since before covid struck. A friend was interested in buying so I pumped up the tyres and got it running again. The brakes were howling and had no power until I gave them a run down a big hill and bedded them in again.

are the axle and freehub bearings all good?

I’d also go with caliper leak. None of the ones I’ve had produced anything visible but were fixed after replacing.

My mate had a simular issue until I gave him a spare Hope adapter to replace the unbranded cheapo lump of alloy that came with his bike I also faced his IS style frame mounts at the same time. So the frame mounts could be a bit off. I always blast my rotors with disc brake cleaner and rub new pads together under the tap to help bedding in.

Does the brake still have decent stopping power? If it does, it’s not a calliper micro leak. If it doesn’t then it likely is a micro leak. I speak from painful experience of having had 6-7 callipers from XTR down to R785 all fail in a similar way.

Leak detection is simple. Any wetness on the rear of the pad plate is a leak. Plus fluid on the pad material would affect braking performance, and he’s(as yet) not reported any issue there.
I’d suggest ,given its down to vibration, the problem lies in the pistons , maybe just a tiny bit of play in them.
As above, change the caliper for another.

FWIW i run ultegra calipers but some cheapass shimano rotors – organic pads only.

At the end of winter i swapped pads for some disco brake pads and instant howl like a banshee. Lower grade shimano rotors dont like any metal pads whatsoever.

Back to resin pads, a bit of squeal. A little brake caliper alignment and all good. Back to silence.

Swap the pads front and back – see if the noise moves. Then try swapping the rotors (as it’s a commuter I’m assuming they are the same size).

If power is good I’d say it’s more of a resonance / vibration issue. I had similar with a Trek Session 10 that I used to own. There was something about the brake set up that caused the rear brake to sound like horrible things were being done to Chewbacca and all the alignment in the world couldn’t stop it. There was no contamination and power was really good. In the end I dropped a rotor size and the brake went silent. You could try organic pads too as they will alter the vibration characteristics of the brake / rotor / frame.
Reminds me of V / cantilever brake days and the ‘correct’ way to keep brakes quiet was to toe them in. But that sometimes just didn’t work. Again one is just fighting the effects of vibration. I’ve toed brakes out, and even one in and one out. Whatever works works!

I was plagued with front brake squeal for a good while, sanded pads, cleaned rotor it just got worse. Finally noticed that the washer on the caliper mount bolts was in the wrong place and so the caliper sat too low on the adapter which also meant the rotor edge was slightly catching top of caliper on hard braking. Only reason I knew this was the rotor edges (Avid) are wavy and they had burnished at the far edges. Caliper was also mounted slightly off/askew so wasn’t 90deg to the rotor. Moved washers, centred caliper. Squeal went away.

pop your front brake on it and try slowing down whilst riding down the street. I had similar (different brake) and it still wailed. Turned out the hub cones were a tiny bit loose, and thats where the vibrations were coming from

I stand corrected. Does appear to be a tiny leak. I’ve swapped the caliper and all seems to be sorted.

I also found the original article about fixing the leak:
Link