Rear Disc Rubbing - Annoying Noise

[brw0513]

The rear disc on my 900e has started making an awful rubbing noise. I've made a short video here:


I've used white paint pen to try and highlight the lateral movement in the disc relative to the caliper. The sound level in the recording is low, and of course the dog was eating kibble in the background. Sheesh.

The wobble in the disc could be the disc itself or the hub, or perhaps something else. I was going to remove the disc and re-orient it 180 degrees on the hub. If the rubbing indication stays in the same place on the disc, then it's likely to be the disc; if it stays in the original location then I'd be suspecting the hub.

This rubbing hasn't always been there. And it's only there now about 90% of the time. But it makes an awful racket at certain speeds and is driving me loopy.

I've recently changed the brake pads and bled the hydraulic circuit. But I bled the circuit before fitting the new pads (bike shop took a while to get them in). I'm wondering if I've actually got too much fluid in the system and the brake pads are prevented from withdrawing away from the disc. The old pads had a mm or so of material remaining and the new pads were a little difficult to fit.

Any suggestions?

Good advice appreciated.

 

[VWsurfbum]

Did you re-centre the caliper?
that amount of disc movement (not the hub) is annoying but not the end of the world. you could try straightening it?

 

[RustyMTB]

These & a little at a time.

I'm not kidding either. The Park tool offering works on exactly the same pricinciple & won't be lying about in your toolbox.

 

[Akelu]

#1 reset the pistons (they slowly inch inwards 'permanently' as the pad material is worn away)
if that doesnt work
#2 true the rotor with above tool

 

[RustyMTB]

If you want to go full belt & braces, then remove the caliper & take the pads out. Use a piece of wood or plastic to keep one piston flush whilst pulling the lever to advance the other a few mm. Don't over do it, the piston can pop out altogether.

When it's extended, use a cotton bud soaked in IPA or brake cleaner & rub it around the piston sides.

Once it's cleaned, use another bud dipped in Mineral fluid if they're Shimano brakes or DOT fluid if SRAM & again, wipe round the piston sides to lube them & push the piston back into the bore. Repeat the extension/retraction a few times until you're sure the pistons are moving freely & repeat for the other side.

When done, be sure to wipe any brake fluid from the piston surfaces & interior of the caliper. Then refit the caliper & centre it both top & bottom by eye so the disc is equidistant from the caliper sides & then wash your hands before refitting the brake pads. Don't be tempted to put the pads in, pull the lever & do up the caliper bolts, it won't centre it.

If it's still rubbing, then your disc has a warp & you can use a tool to straighten it. You can straighten the disc first but if you follow the steps in order, then you'll know your brakes are serviced & working as they should do which will give you a clear view of where the problem lies.

 

[brw0513]

Thanks for all the advice. It was very helpful.

It seems the pair of pistons, on the wheel side of the caliper, are sticky. So I'll spend more time to thoroughly treat the external areas as suggested above.

I'd like to disassemble the caliper and overhaul it. But it seems Shimano don't sell a seal kit. Surely this can't be true?