Disc Brake Piston alignment issue

joaop

hey guys,

I aligned the rotor with the pads, everything looks good, the rotor can turn without any noise or contact, then I go outside and after some brakes, I can see the left pad is touching the rotor.

I realigned the rotor again, but the left pad keeps touching the rotor again after some brakes.

This is what is happening:


Do you know how can I solve it?

ibr17xvii

Sticky piston.

Remove the wheel & pump the brake lever so both pistons are out as far as you can without them both popping out & give them a clean, I use isopropyl alcohol personally. Maybe use a cotton bud & lightly grease them with some Shimano mineral oil which will also remove dirt around the seals.

Push them both back in, pump the lever & see if that's any better. You can also pump the lever whilst holding the non sticky piston in so the other one comes out to see if that improves it.

Plenty of YT videos on the subject if you're struggling.

joaop

Thanks for the tips, I'll try it. My disc brake is Shimano Ultegra R8020.

Charlie_Croker

There are two posts for this problem running side by side.

Firstly do you have one or two pistons per caliper? I suspect looking at your diagram you have just a single piston, on the left. Can you verify?

pamplemoose

joaop said:

Thanks for the tips, I'll try it. My disc brake is Shimano Ultegra R8020.

Have you tried loosening the bolts that mount the calliper to the frame/fork, then holding down the brake lever whilst tightening up the calliper bolts? That fixes 99% of rotor rub problems for me.

photonic69

I had this exact problem. It appeared to be a build-up of crud/brake dust around the piston on one side. This is what I did:

Take wheel off. Take pads out (useful to have a repair stand to do this)
Get an old toothbrush (or use partner's). Cut the bristles off short 3-4mm long.
Get some degreaser/fairly liquid and give both pistons a good scrubbing. Rinse off well.
Use a plastic tyre lever to push both pistons back as far as possible. (Park Tool blues ones work well for this).
Whilst holding one piston back operate brake lever gently to get piston out a bit. Push back with tyre lever. Repeat a number of times.
Repeat procedure on other piston.
Give a good brush down with toothbrush and soap again.
Dry off and put everything back together.
Put wheel back in and you'll need to pump brake lever an alarming number of times to get the pistons back out again.
Pump levers about 20x when they are in contact with the disk.
Recenter the caliper to give equal clearance for the pads/disks.
Go for test ride.

This worked for me when I did it before Christmas and it seems to still be OK today.

Hope this helps.

ibr17xvii

Charlie_Croker said:

There are two posts for this problem running side by side.

Firstly do you have one or two pistons per caliper? I suspect looking at your diagram you have just a single piston, on the left. Can you verify?

If he has Ultegra calipers I'm pretty sure he will have 2 pistons per caliper.

joaop

Charlie_Croker said:

There are two posts for this problem running side by side.

Firstly do you have one or two pistons per caliper? I suspect looking at your diagram you have just a single piston, on the left. Can you verify?

I have two pistons.

Charlie_Croker

Something is sticking then by the sounds of things
You could try pushing each piston out in turn, cleaning up and lubricating what you can and then pushing back in.
If that doesn’t work then you’re going to have to take the pistons out and clean them, and the body of the caliper, that'll mean a full bleed of course