right, i think i’ve eliminated the headset, forks, wheel bearings, caliper mounting bolts etc. the only thing i can find that is loose is one of the brake pads moves backwards and forwards on it’s mounting pin. haven’t got any spares to test, but do you think this could be the culprit?

Not clear if you’re talking about disc or rim brakes.

If it’s the former, it could be a warped rotor. Spin the wheel while looking edge-on to the disc and it should be obvious if there’s a wobble. You can fix it by clamping a clean adjustable spanner over where the warp is and just bending it out.

If mine get even the tiniest spot of oil on the pads or disc I get a horrific judder and braking at low speed results in a noise like a goose being assaulted

What brake is it? I’ve found some rotors (such as the older avid ones) judder just by virtue of their shape.

My Hope Mono brakes judder, its the pads binding on the rotor arms. Can’t feel the rear doing it whilst riding but if you roll the bike along its obvious.

Changed the front rotor for a Shimano XT one which solved it for a few months but its back again now…might try sticking the Hope rotor back on and just alternate them if it fixes it.

Anyone know if a Magura rotor will fit a Hope mono? 160 rotor. (Maguras have some patent thingy which means they can produce a wavy disc without that has the same surface area all the way round)

But we are told disc brakes are fit and forget!

Try lightly deglazing the pads with emery cloth lad on a flat surface. Clean the rotor thoroughly. First with a dry clean rag to get exces crxp off, then use neat washing up liquid and rinse with hot water, then rinse again until absolutely gunge free. Dry off and try again. If you are still getting juddering, you might have an unevenly worn rotor. The only fix is to replace the rotor. I had one replaced FOC by Hope. (Hope after sales support is first class btw). If it’s only one of the rotors that judders, try swapping them between front and rear (assuming you have the same diameter discs). If the fault moves with the rotor, you have your diagnosis.

I had something simular…turned out to be a crap wheel QR. The thread on the end nut wasn’t square with the shaft so even though the wheel felt tight under heavy braking the wheel could move a little…causing the brake to judder.

they’re avid juicy’s so it could be the rotor shape i suppose. sadly front is 185 and rear is 160 so can’t do an easy swap. it’s really starting to irritate me now though. think i’ll spend most of saturday trying to work out what’s going on.

the rotor is one of these:
http://www.chainreactioncycles.com/Models.aspx?ModelID=15263

That rotor should be fine. It was the ones before that that were a problem.

Re the advice above about cleaning the rotor – I always find that that makes any problems worse. I never clean mine (other than with the hose when hosing the whole bike down).
Worth trying a rotor/wheel swap if you can though.

Perhaps you could swap the pads between front and rear. That would be a simple exercise and will eliminate your loose pad concern. Thinking about it, the pad seems a likely offender. That’d be a relatively cheap fix if it proved to be the cause of the fault.

If that makes no difference, maybe you could swap the whole rear caliper on the rear to the front on a temporary basis (coiling up the excess hose with a tie wrap). Leaving the front coiled up on the bars, again on a tie wrap.

Just step through each thing one at a time to see what changes.

Good luck!

Stand by the bike and gently hold the brake on whilst rolling it along. If you can feel the brake grabbing you can then work out if its the wavy bits, the rotor arms, etc.

When I tried this on my brakes it was obvious as you could feel the brakes grab as the pads passed over the rotor arms.