New Bike with that gurgling brake noise.

[billium]

My new Ride1Up 700 has that weird brake noise on my rear wheel - often described as gurgling or underwater or toilet flushing. Several threads here and elsewhere about the issue with some reporting success changing the pad material - but not really explaining why only some bikes have the issue.
Brake disk is true and clean - so are the pads.
Closer inspection revealed that pressing the brake is flexing the disk to one side by about 0.25mm ( measured with a dial indicator gauge) which 'might' be the source of the problem. Both pistons are moving but presumably one has more force.

I don't know enough about bicycle hydraulic brakes to tell if this is acceptable or if there is something wrong - it sure smells wrong to me since front brake disk flexes only 0.02mm when pressed.
I could see having air in the system making the brake spongy but even if air was in only in one piston chamber it would not change the pressure of the system so I am confused.

Any ideas what may be happening?

 

[Gionnirocket]

Could very well be that the caliper is not centered properly. In general the process is to loosen the bolts on the caliper, squeeze the brake fully and hold while tightening the bolts again. If you require a third hand use a cable tie or similar to hold the brake handle.
Additionally some brakes have other adjustments and try to locate the instructions for yours.
Lastly... New pads need to be broken in and applying heavy breaking before doing so can glaze the pads. Sometimes scuffing them up with sandpaper helps to remove the glaze.
There's quite a few videos on all this on YouTube... The Park Tool ones on this are pretty good.

 

[JRA]

Check the cutouts on the disc surface the pads contact for any raised edges and smooth out. If they are smooth check to make sure you pads are fully in contact with the braking surface. If not readjust the caliper via the bolts that hold it by taking out or putting in washer(s).

 

[billium]

I have tried centering the caliper using line of sight and the tighten while brake is applied methods. I have checked disk for sharp edges and inspected & sanded the pads with no change.
The core issue remains:
Applying the brake is pushing the disk to one side - something that is possible with one piston and a sticking floating caliper but should not be possible with dual pistons since the pressure is the same at each pad.
I suppose if the mount is not holding the caliper at precisely 90 deg to the plane of the disk then one pad's inner edge would catch first and then other pad's outer edge would catch first with more mechanical advantage but eyeballing it looks pretty square to me.

Here is a video of the issue - I am pumping the brake about once per second - look first at center right to see the white gap between the pads and the disk coming and going - then look center left to see the edge of the disk flexing down.
It was difficult to hold the phone steady in the best spot but at one point you can see the same amount of white gap between the pads showing caliper is well centered.
Same brake on front wheel does not visibly flex at all.

Brake

New item added to shared album

photos.app.goo.gl

 

[Gionnirocket]

Possible that some grime on one piston is causing it to not fully deploy?
Also sometimes the "proper procedure" doesn't always provide perfect centering results and manually cheating the caliper to one side is required.
Bicycle hardware is not built to NASA.. nor automotive specs/tolerances.
I wouldn't drive myself crazy expecting perfection. As for the noise... The pads are typically guilty whether contaminated, glazed, poor quality or defective.

 

[AHicks]

From an automotive perspective, the organic pads are far less picky and much less likely to make noise. Organics should be available for your bike.

Have you looked at break in procedures? This latest bike of mine started out quiet, but then started squeaking out of the blue while just going down the road. Mine would shut up for a while if I grabbed a quick hard apply and release. I used that brake only for a while (nice easy stops), and within 25 miles or so it's shut up completely. Now at 200 miles, it's behaving nicely. -Al

 

[billium]

Yes I have payed attention to break-in but this is not traditional squealing.
Here is a video from someone else with the same horrible noise.

I think the pads are not pressing flat against the disk and are twisting it and catching in the rain slots.
Organic pads are softer and may just hide the issue.
I tried loosening the caliper just for testing and its fixed! No more noise - which tends to confirm my theory since a loose caliper will settle and allow the pads to press flush. Of course I can't leave it loose.
Calipers are designed to adjust left and right at the bolts so any twist in the plane of the bolts can easily be corrected by loosening and holding the brake hard down while tightening but if the mounting bosses are leaning a little then the whole caliper leans and that cannot be corrected.
Still not proven yet - I need to find a really flat bar to lay in place of the caliper to actually measure the angle between mounting boss plane to the disk radial plane which should be 90 deg.
If I am right then the problem will go away eventually as the pads will wear themselves into a wedge shape to sit flush against the disk or I can file the tops of the bosses to correct the lean.

 

[Gionnirocket]

Good eye!
Like I said... not NASA tolerances

Watch this video.. especially the last minute:

And you seem knowledgeable and good with tools so here's another video that may be helpful:

 

[billium]

Thanks - excellent videos by Park.
The mere existence of the DT 5.2 tool says a lot...

I am a retired Engineer so I actually enjoy solving problems like this.
I will update the thread with any findings.

 

[AHicks]

Thanks - excellent videos by Park.
The mere existence of the DT 5.2 tool says a lot...

I am a retired Engineer so I actually enjoy solving problems like this.
I will update the thread with any findings.

You're going to make an excellent bike mechanic! No rocket science involved. Just a basic mechanical aptitude and a little patience will go a long way here. There's a lot of guys here, that have already been there, done that, that are more than willing to share their experience as well. -Al

 

[Gionnirocket]

Thanks - excellent videos by Park.
The mere existence of the DT 5.2 tool says a lot...

I am a retired Engineer so I actually enjoy solving problems like this.
I will update the thread with any findings.

I as well... Keeps the gears turning.

I'm sure that tool is expensive so possibly a local bike shop can help if you aren't able to make the necessary adjustments.
Or perhaps a bit of well controlled filing and/or some conical washers can get you there.
Good luck.. I have the feeling you got this one way or the other.

 

[Gracchus]

Hey, any up date to this? I have the same gurgling noise and trying to troubleshoot it.