Hey guys, trying to fix up a gt sanction 2014 for a friend. I replaced the bushings in the i-drive pivot near the bb as there was play in it, cant find play in any of the other bearings or bushing in the frame.

When the rear brake is locked or used heavily there is a massive vibration up through the frame, regardless of positioning on the bike. it starts at the rear but is so strong it can be felt up through the bars.

The bearings in the rear wheel have no play and ive tightened the axle way up. I tried a different wheel with a different rotor (that i know to be good) and it slightly reduced the vibration, im putting that down to bigger volume tyre though.

I also tried a different brake and that made zero difference, ive clamped the caliper bolts way past recommended torque no difference. I also over tightened the headset (bearings need replacing but theres no play in it) to see if that could be it but no.

I fix up mtb’s for a living part time so im not completely clueless (i think  ) but this is completely throwing me, ive checked everything to the best of my abilities and ive found no solution. Anyone here have any ideas? I would appreciate anything at this stage.

Are there any cracks anywhere? I had horrendous vibration levels from a rear brake leading up to the dropout removing itself from the frame.

different wheel,tyre, disk, brake (and I assume pads) – I’d be looking at the frame.

I had a similar sounding issue and I found the cassette lock ring had come loose, i must have forgot to tighten properly.  It make a horrible sound and rattled like crazy when braking.

id be thinking its the frame too except the only pivot that had play i just replaced the 2 bushings in it, i assumed that was what was causing the issue in the first place but nope 😀 i just faced the caliper bolt mounts and nada either. I didnt spot any cracks anywhere in the frame but il have another look to make sure.

Im not sure the cassette could be causing the issue as it happens any power down on the pedals, i can literally drag it while walking and get the vibrations, ill check either way just in case though, could be anything at this stage.

If you can do it at walking place it should be easier to see where it’s originating?

… or it is just very unfortunate combination of pads/rotor/frame alignment.

Friend of mine have it on his Canfield Riot. He duck taped 2 inch bolt to break side seatstay and all the sudden no vibrations.

Cheers!

I.

Cracked axle?

Other than that yeah a bit of bad luck. I know one of my mates worked for an automotive brake supplier, and they spent a lot of time making sure nothing had resonanant frequencies that could be excited by the braking. I’ve only heard of one cycle brake manufacturer that claims to have considered it, and that was in stuff at this year’s Eurobike so probably not released yet (the new Hayes brake I think).

So maybe it’s just destined to squeal. Something to detune it like the bolt taped to the rear triangle might solve it…

Had this with a warped disc, worth a try.

disk is definitely not the problem as i tried a vented floating rotor from my own bike and it didnt stop it, seems to originate from the hub/axle area but i really cant see anything wrong with them, thru-axle seems straight and uncracked, cant be the hub either as i tried my own rear 142×12 wheel and it only reduced it a small bit. bit of a head scratcher this one, might try taping a bolt or two onto the rear triangle to see if it does anything. But its not so much a sound as it is a judder/vibration that can be felt.

Thanks for all the suggestions lads, appreciate it 🙂

Caliper not aligned correctly?

I get this with a 200mm rotor on the back. Tried different rotors, alignment etc and its just the extra leverage off a big rotor  that makes Chewbacca angry.

The old Stumpjumper Evos were prone to this, switching to floating rotors fixed mine as it wailed and ate brake pads.  Looks like you’ve tried that though.

Wasn’t there a fix with old Avid brakes than involved glueing a pound coin to the caliper?

I had the same problem with some avids on a hardtail and swapped everything trying to get rid of the vibration with no luck.

Swapped to a Shimano caliper and no more vibration.

I’ve had a loose derailleur hanger cause this before

the calipers on the bike are zee, i tried the bike with an avid elixer as well but same issue