My M785 XT rear brake makes an horrendous grinding noise when applied and vibration is so bad I can feel it in the lever. I have a 180mm Ice tech rotor and metallic pads.

I have checked all possible causes and drawn a blank.
Caliper is perfectly centered, as are the pads with no rub and an even bite. It is correctly bled with no air in the system and there are no leaks. I changed to these pads recently as the original one made the same noise and I bedded them in correctly. Finally I checked all bolts were correctly torqued and the frame has been correctly faced.

My front brake has been perfect with zero issues and the rear brake has great bite and loads of power but the grinding and vibration is awful.

The only thing I can see that’s obvious is that the pads move around a lot in the caliper, around 2-3 mm fore and aft and I don’t know if that’s normal.

Any ideas?

Definitely not normal to have that much movement, i’d expect a lot of similar noises if my pads moved that much. Have you got the correct pads fitted, some of the Avid and Formula pads look similar to the latest Shimano, maybe you’ve been given some of these by accident.

They were advertised as genuine shimano pads but that doesn’t mean they are! Will investigate.

Maybe compare with the fronts to be sure.

Double checked they are Shimano metal pads the correct type. Compared to the front pretty much the same pad movement until it bites but I think my estimate of 2-3mm movement was a bit much.

It’s as if the pad is contaminated as there is an awful lot of noise but can find no evidence of a leak and these pads are just 5 rides old.

Maybe give the EBC pads a go to see if it improves things.

Careless use of spray on chain lube is also a frequent cause of contaminated rear pads.

Never use sprays on my bike, only water and bottle oil on the chain.

Probably won’t be that then 🙂

Swap pads front to back to see if pads are the problem

Yeah thought of that but the pads I have were put in last week in order to see if it was the previous pads!

Maybe I have a dodgy rotor, which I have also stripped and cleaned with brake cleaner.

What type of rotor are you using(and is it fitted backwards), saw-tooths, waveys, massively cut away types, and ones where the pad overhangs the braking surface and catches the spokes often cause vibration too. Did you clean the rotor before fitting the new pads, or after?

What type of rotor are you using(and is it fitted backwards), saw-tooths, waveys, massively cut away types, and ones where the pad overhangs the braking surface and catches the spokes often cause vibration too. Did you clean the rotor before fitting the new pads, or after?

Using Shimano 180mm Ice Tech rotors correctly fitted and torqued. Cleaned the rotors before fitting new pads.

My next fix is to try a new rotor and 180 adapter to rule out a badly made part that doesn’t quite align.

If you’ve run out of ideas, you could check the bolts etc holding the caliper/adapter to the frame. I’ve had terrible vibrations from a rear Avid brake before, which turned out to be due to a cracked washer.

Try organic rather than sintered would be my suggestion to see if you still have the grinding noise. If you do it rules out the pads. I find that sintered do make more of a grinding noise than organics.

Also is the disc centered in the caliper slot?
Make sure that one piston isnt working more than the other and pushing the disc into the caliper or mount.

Try organic rather than sintered would be my suggestion to see if you still have the grinding noise. If you do it rules out the pads. I find that sintered do make more of a grinding noise than organics.

don’t get organic pads wet (or feed them after midnight…)

It was more a suggestion to rule out the source of the grinding noise.
I tend to run sintered all year round, but had a set of organic pads kicking about, so given it was nice and dry banged them in. They work well in the dry, don’t doubt they’ll last 5 minutes in the mud though.

That sounds like both annoying and frustrating and it would seem you are going through an appropriate process of elimination.

Have they always made this noise? The suggestion above of checking the rotation of the rotors was my first thought, even to the point of whether the spokes are laced correctly?

Have you checked your hub bearings?

You can unhelpfully wash the chain oil onto the back brake if you use some kind of spray washer sideways 😳

Have a go with MucOff disc brake cleaner (spray rotor & pads, sand pads, spray pads again) and sanding the top layer off the pads off with a little chamfer front and back to reduce judder.

Worked for me (same brakes, horrible squeal appeared out back and now is gone). I also gave the calliper a squirt when the pads were out in case anything got in behind the pads. As mentioned, a central calliper is important for it all to work optimally.

Do you ride where it’s sandy? Possible debris embedded in the pads?

Thanks for all the tips but as I said earlier I have tried ALL of these solutions with no positive outcome. The front brake is faultless and came as part of the f + rear set but the rear has vibrated from the start. Very frustrating as the power and bite is fantastic.

Today I tried a non-ice tech rotor and exactly the same issue, it’s a resonance that emanates from the brake right through the whole frame and I can even feel it through the pedals.

Rear wheel all ok and no hub issues.

Difficult to send back under warranty as to look at the brake has no obvious defect.

Have you tried the rotor on a different wheel to check it’s not the hub? Or even swap the brake to a different frame if poss? Not from experience but you seem to have tried most things.

my mate has exactly this problem on a new bike. i cant figure it either. tried most of the above except new pads and rotor. keep us posted if you find a fix

I have tried a different wheel with same outcome.

The next thing to try is a non shimano adapter.

Then finally the brake on another frame.

I had this issue with a rear shimano deore about 3 year ago it’s so frustrating I tried all the things you have tried with the same outcome. Eventually bought a new brake set as couldn’t live with the vibration. Would love to know the problem as it haunted me for about 2 month

I Had this problem when I fitted a new slx brake to my bike and tried all the tricks i knew but to no avail. What did work was to use a smaller rotor. I was running a 200 and dropped to a 180 and was perfect. Obviously changing adaptors at the same time. Bizzare but it was like I was over braked. It might be worth trying a 160?

Of the previous generation of shimano disc brakes – the LX, XT and XTR (960 and 970) All used the same pads. I’ve used all threemodels However the lx always howled/sqealed/ vibrated (2 pairs plus pair on my mates bikes) whereas the other models never did. Never discovered why despite incessant tinkering with different pads/discs/mounts.