Why does my RS125 judder?

Q. I’ve noticed a problem when using the front brake on my 2008 RS125. Sometimes, when braking lightly, the whole front of the bike starts vibrating quite violently – it’s not a massive problem but it is disconcerting.

It doesn’t happen when braking harder. I’ve checked the disc and it’s not warped. Could it be that the pads are loose in the caliper?

The bike’s just been serviced and passed an MOT and no problems came up there.
Jahagon, MCN forums
 
A. If it sailed through an MoT, possible causes like a leaking fork seal contaminating the pads, orindeed worn pads shouldn’t be a cause. If you apply the front brake lightly, carefully feel the pads with your fingers.

They should move about a bit then tighten up as they put pressure on the disc itself, but without the disc moving towards either pad. If the disc flexes the caliper is not floating.

Do you feel or hear any clonking when braking hard? That would indicate wear in the steering head, wheel bearings or fork sliders.

Sometimes when the front end of a bike is lifted for a service it seems to allow any wear that has taken place in the steering head bearing surfaces to become noticeable once the bike is lowered and then ridden again.