UKC

Juddering disc brake

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 Theho 03 Feb 2022

Hi

My cyclocross bike rear brake has developed a pretty bad squeal at low speeds which turns into a massive juddering event as you apply more pressure approaching a stop. I initially changed the pads and cleaned the discs and checked the brake calliper was tight. No improvement. The discs didn't seem worn and the thickness was still above about 1.65mm, but I've never changed it nonetheless. Still no improvement. Where do I go next - other than the LBS (as I wouldn't be asking on here!)

Any informed ideas would be appreciated.

John

 Yanis Nayu 03 Feb 2022
In reply to Theho:

Have you tried loosening the calliper and re-tightening while holding the brake lever down? That’s more a technique for stopping rubbing but I could imagine everything being slightly off-centre wouldn’t help. I don’t think it will work but only takes a few seconds. When I’ve had that thorough cleaning has been the answer. Is there a way of checking the rotor isn’t bent - uneven rub on the brake pads perhaps?

OP Theho 03 Feb 2022
In reply to Yanis Nayu:

There's no rubbing but you've made me wonder if the pistons are moving equally - I'll check and lube them if they're not and re-centre the calliper. I'll let you know how I get on.

Thanks

 TobyA 03 Feb 2022
In reply to Theho:

Rotor warped? Or loose somehow?

 Yanis Nayu 03 Feb 2022
In reply to Theho:

That’s a good point. 

 LastBoyScout 03 Feb 2022
In reply to Theho:

Assuming they are hydraulic, it could be air in the caliper - heats up under braking and expands.

You seem to have changed everything else, so that would be my next step.

OP Theho 03 Feb 2022
In reply to LastBoyScout:

Okay, i'll try that too.

thanks

1
 Mick Bradshaw 03 Feb 2022
In reply to Theho:

I recently tried to cure a very similar problem on a friend's bike - tried cleaning the disc (which was true) re-centring caliper, cleaned the pads and then changed the pads for new ones - nothing resolved it. Friend ended up going to the LBS who changed the disc and the pads together and fixed it. I still don't understand what was causing the squealing/ juddering but had never heard/ felt anything as bad as that.

 gethin_allen 03 Feb 2022
In reply to Theho:

Seems to be a bit of a recent thing, my front brake started doing the same on the weekend, maybe the wear of all the winter crud has finally caught up with us.

My plan when I finally bite the bullet and go into the freezing cold garage is to sand down the pads and the discs a bit with some aluminium oxide paper, give it a squirt with cleaner and hope that does the job.

 gethin_allen 03 Feb 2022
In reply to Theho:

Just back from the garage for a review.

As I mentioned above, sanded and cleaned the pads and rotors. Rear brake now superbly sharp. Front brake work identified that the headset is loose/full of skank and this was part of the judder issue. Maybe worth checking.

 Mikek 03 Feb 2022
In reply to Theho:

After a recent road ride I probably hadn't cleaned my bike sufficiently as next ride 2 weeks later my front disc was really squealing. My go to cure has always been to clean disc with meths but this time I could only find car windscreen de-icer so squirted this on and cleaned including all the cut outs which appeared to have a thin layer of maybe salt particles. Then push bike with brake on, clean again etc and seems OK now - so I guess winter road crud is to blame and me not being vigilant enough?

 Monk 03 Feb 2022
In reply to gethin_allen:

> Seems to be a bit of a recent thing, my front brake started doing the same on the weekend, maybe the wear of all the winter crud has finally caught up with us.

> My plan when I finally bite the bullet and go into the freezing cold garage is to sand down the pads and the discs a bit with some aluminium oxide paper, give it a squirt with cleaner and hope that does the job.

If it's a front brake, check your headset/ bars are tight enough. The pressure from braking can exacerbate any play

Edited to acknowledge that you already discovered this! Took me a while first time it happened

Post edited at 20:28
 coachio 03 Feb 2022
In reply to Theho:

I had this for nearly two years. Tried centering the caliper, cleaning the brakes after every run, changed the rotor, bled the system and then put it into lbs. No improvement. Eventually changed the full set up. Turned out it was a miniscule leak from the caliper. It left a very very fine residue that you would probably only pick up when knowing what to look for.

 fire_munki 03 Feb 2022
In reply to Theho:

Don't lube the pistons, only found this out today reading an interview with a Magura bod.

There needs to be friction on the rubber seals as that is what drags them back into the calliper.

 Jon Greengrass 04 Feb 2022
In reply to Theho:

Organic or sintered pads?

Do you wash your bike regularly?

 Baz P 05 Feb 2022
In reply to Theho:

On a car this is caused by vibration of the pads which is cured by smearing a small amount of Copperslip grease on he back of the pads. Never tried this on the bike but if you’ve tried everything else ——


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