Front brake calliper shimano deore brm 596. Pads are rocking back and forth causing vibration when braking. Could this be the piston moving? Do I need to replace a seal? Brake is not leaking fluid. I’ve changed pads, pad holder and split pin for new and swapped parts with rear brake to double check. Brakes are in good condition, not had this before! Cheers.

They will move, the pad needs to have some clearance in the caliper or it wouldn’t work.

I’d not be (immediately) blaming pad movement on brake noise, there are lots of other possibilities.

Could the caliper be slightly off centre thus causing the judder? I’m sure my pads have that tiny bit of movement and never had any noise issues.

Checked and re aligned pads. If I squeeze lever lightly I can rock wheel back and forth slightly. Pads are moving in calliper, as if the split pin was too small if you see what I mean.

That’s what they are meant to do.

Everything from Alivio to XTR. If they didn’t rock like that, they wouldn’t move in and out, and you’d have no brakes. Or your brakes would be on all the time.

I’d be checking stuff like disc contamination/wear, caliper out of alignment, fork bushes, headset……. and so on.

I’ve had this before – check your disc bolts are done up tightly 😳

There needs to be some movement of the pads within the caliper.

The caliper and the disc should be securely mounted with no movement.
Centre the caliper over the disc by eye, so that the disc is central in the caliper slot. Dont use the squeeze the brake on to centre the caliper, because it wont and its not best practice.