Front disc/fork vibration when braking.

manc_ian

Hi.

Ive got a Giant XTC SX with Reba SL forks fitted, standard MPH brakes with Aztec Rotors (180 on the front).

When im braking on a downhill section i get a lot of vibration at the bottom of my forks. If i look down whilst braking i can see the fork vibratiing alot (bending forwards and backwards). I fitted new pads to see if this helped and it just went worse. When im stoped, if i put the front brake on and rock the bike back and forth i can feel i a very small click/clunk through my handlebars.

Ive just had my bike serviced at my LBS and he checked over the front end and could not find anything wrong with it. He suggested that the forks will have a little flex in them which is normal and having a big rotor might not help. He suggested possibly fitting a Hope Floating Rotor to see if this cured the problem.

Im just wondering if its the Aztec Rotor as its a wave design compared to the standard round design of the giant rotor. But there was no vibration when i first fitted the aztec rotors.

Could anyone else shine a light on this problem and possibly advise what the problem might be?

Help would be much appreciated.

Ian

nicklouse

put your hand over the joints and rock the bike with the brake on. the joints being stantion into lower and then top and bottom of headset. also turn the fork at 90 degrees to the frame and do the same.

so where is the movement?

FSR_XC

I have the same problem - Avid Juicy 3's with 203mm disc.

Took it in to get the headset tightened (new one, so free to get done). It had been a little loose and obviously hidden the problem. They also adjusted the brakes while they had it.

Picked it up & straight on a ride this morning. On the road there was an obvious judder. We went through the normal checks of Headset, forks, calliper, pads etc, but nothing noticeably wrong.

After ride, back to LBS ('cause they love working on muddy bikes!) Nothing found. Only thought was the brakes 'grabbing' the disc due to contamination or pad wear.

I am changing the pads this week (and cleaning rotors) so going to see if there is an improvement.

ian_watson

I think I have the same vibration.

When you break with the front break lots of force moves forward (bike and rider) . Because the forks are slightly flexible the front wheel moves slightly towards the rear wheel. After a small amount of movement towards the rear wheel, it then springs forwards - and it continues until you stop or release the break.

On my bike I can actually see the bottom of the forks moving very fast. Its only a few millimeters of movement.

I suppose that in theory this movement of the wheel means that the front wheel speed decreases and increases at each cycle of vibration.

Ian