Shimano XTR front brake makes strange noise on new bike

When bedding in the brakes of my new Haibike Lyke SE (purchased online), I noticed that the front brake was making strange noises. A kind of fluttering sound. Apart from the low performance, precisely because it hasn't been broken in yet, it doesn't feel bad in terms of pressure point or braking effect. Actually, it's just like the rear brake was at first, which, however, doesn't make any noise and now has much more braking power thanks to the process.

I've already checked several things.
The brake caliper is securely bolted, the disc is straight and runs smoothly. The inch bolt on the Fox 36 is tightened to the correct torque after multiple compressions. The rotor and brake pads are clean and show no signs of contamination or glazing.

The relevant specs:
- Shimano XTR M9120 brakes (front: 203 mm, rear: 180 mm, organic pads)
- Mavic E-Crossmax XL R Carbon wheelset
- FOX 36 Float Factory fork (quick release)

I tried to record this in a short clip.
Unfortunately, it's harder to hear in the recording than in real life.
You have to turn the volume up quite a bit.
Maybe someone has an idea what the problem could be based on this.

If you have Shimano XTR N03A resin disc brake pads with cooling fins, could be those 'fluttering'.

Sounds like cable rub on the tyre knobs. Check if front cable is rubbing. If it isn't.

Confirm it is coming from the pads or rotor, by removing the pads and riding. If it is. Then replace rotor and pads, one at a time, to see which it is. If still there. Then replace both.

If it isn't coming from them. Keep removing things that could be causing it, like the whole caliper, till you identify the source.

I have a very slight almost so soft that it is not able to be heard noise and sensation in the brake lever on my XT's that I believe is from the slots in the rotor. I wonder if you were to press the pads into the brake caliper so there is a gap to the rotor to see if it is "pad to rotor" noise.

same on mine on front, i suspect I ned to replace the rotor

Ndanger said:

I have a very slight almost so soft that it is not able to be heard noise and sensation in the brake lever on my XT's that I believe is from the slots in the rotor. I wonder if you were to press the pads into the brake caliper so there is a gap to the rotor to see if it is "pad to rotor" noise.

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I get the same noise with my front brake using a Galfer rotor, it's just the holes in the rotor, nothing to worry about

Same here with my hope floating rotors. Swapped them to a different bike to try and it’s the same. It must be the holes passing through the pads.

Thank you all very much for your assessments.

Unfortunately, however, they do not apply in this case.

I tested installing the front wheel of my Trek Rail 9.8 in the Lyke, along with its brake pads. (Also 4-piston Shimano brakes and 203 rotor, only SLX instead of XTR, brake pads the identical model).
And there were the same noises, which means that the rotor, the pads, and other sources such as the wheel can be ruled out.
The Rail doesn't make these noises – I tried it again just to be sure.

Furthermore, when replacing the pads, I noticed that they always have damp marks from the pistons on the OUTSIDE. I always wiped them off, but when I changed/checked them again, there were round marks again. None of this got onto the inside of the pads or the disc (nothing contaminated), but obviously some oil is leaking onto the pistons (checked every 10 braking operations).

There may be a connection.
Furthermore, running in the brakes has had no effect. There have now been at least 40 gentle braking operations, and the braking behavior has not changed, in contrast to the rear brake.

Since the sound of the brakes didn't come across very well in the previous video and was rather drowned out by the freewheeling noise of the motor, I got a Bluetooth microphone and placed it directly near the brake caliper.

As a result, the sound of the brakes in the new video is extremely loud, obviously much louder than it is perceivable when riding, but perhaps easier to assess now.

The following photos show the placement of the microphone and the marks on the outside of the pads.

Could you show the pad side of the brake pads to help see how the wear / alignment indications appear.

Ndanger said:

Could you show the pad side of the brake pads to help see how the wear / alignment indications appear.

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Of course. Here are three photos with different lighting.

When I looked at the rotors that you pictured in a post, for some reason it seemed to me that the pads were not positioned in the center of the rotor surface. That is the reason I asked about the pad surface. I got the impression that the pads were running too close to the slots at the bottom of the rotor as if the caliper was mounted too high.

In your photo of the pad surface am I seeing that the top ~10% of the pad is not touching the rotor? Regardless of what the alignment is from the factory I would be inclined to find a way to lower the caliper or find a disk that has a larger diameter as a starting point.

Agreed, it looks like your pads should be sitting a couple of millimetres lower on the disk. Do you have a 203mm adapter spacer on there by any chance? If not, you might consider getting your mount posts trued. Here’s a photo of what the rotor wear pattern should look like. Note: this rotor is worn to WAAAAYYYY below minimum thickness (enough that I’ve exposed the aluminum sub-layer on the back side), but it accentuates the wear pattern well.

I understand how you two came to this conclusion.
I have attached a few more photos, because I don't think the caliper has any room to go any lower. Or am I wrong? There are also some marks visible on the rotor that provide information about the positioning.

Could you confirm the bike has the correct caliper mount. I suspect that it is for a different bike that yours. Second would be to confirm the correct rotor for the bike. Eg 200 / 203

Ndanger said:

Could you confirm the bike has the correct caliper mount. I suspect that it is for a different bike that yours. Second would be to confirm the correct rotor for the bike. Eg 200 / 203

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Yes absolutely, It's the RT-MT900-L, which is the 203mm internal variant (Shimano does not even offer 200mm rotors, as far as I know).
And it's also the correct adapter SM-MA-F203P/PM - the right fit for the 180PM on the Fox 36.



I've also checked the number of washers and their positions, which are also perfectly right.