rbrides

Simply, one of the pistons does not return after releasing the front brakes on my road bike’s Shimano Ultegra hydraulic disc brakes and causes the dreaded brake squeal. Usually the squeal goes away when I lightly pump the brake 3-4. Sometimes it it needs 8-10 pumps. No squeal while applying the brakes, only after releasing them.

I’ve follow all the procedures I know to clean pistons and calipers, including Park Tools’ and other reliable sources. Changing pads and spring clips has not resolved the issue. I’ve tried to determine if the piston is mis-aligned and thus not moving in/out properly but it does not appear to be so.

any practical advice from others who have experienced and resolved this issue?

cxwrench

Either you're not actually cleaning/lubing them or it's some other mystery. A piston that's mostly in the bore can't be 'mis-aligned'. If it's mostly out of the bore that's another story.

andrewclaus

Have you exercised each piston independently to assure the seals are clean and functioning? If so, it may be time to replace seals and pistons.

rbrides

I am able to push them fully back in. I clean them with Isopropyl alcohol. What is your method for lubing them?

rbrides

"independently", maybe not. I remove the pads and pump them to expose the pistons for cleaning and press them back in, work them in/out a few times pumping the brake lever and push in again. What do you do? Hold one in and work the other "independently"?

andrewclaus

Yep. Get an assistant to work the lever slowly, push piston back in if needed, get each piston to react identically. I saw that in one of the Park Tools videos. Maybe you missed that one--there are a few of them. Careful cleaning first is key.

Polaris OBark

Probably the safest thing to lubricate (if absolutely necessary) is Shimano mineral oil. Use about 1/10th what you think you need, and then spend the rest of the day wiping it off. Any extra will be a dust magnet and make the problem 10 times worse than it is now.

vespasianus

First, when the pads are out, clean with alcohol. Let it dry and gently, and I mean gently, pump the brake lever once and see the piston extend out a bit. Pump the lever one or two more times gently to have the pistons extend out.

Now, get a Q-tip and a little bit of mineral oil (if that is what your brake uses). Dip the Q-tip head into the oil and use it to moisten all around the exposed piston. Get the piston nice and moist with the mineral oil.

After you have coated the pistons well (and really focusing on the part right where the seals are) push the pistons back into the caliper using a plastic tire lever.

Repeat the process (but skip the alcohol wipe) maybe 2-5 times. After the last "push back" of the pistons, clean with alcohol and put back your pads.

rbrides

Thanks.

rbrides

Thanks

Polaris OBark

@vespasianus for the win (detail)

cxwrench

Q-tip and Shimano mineral oil.

greysquirrel

I had a GRX disc brake that did the same thing. Tried cleaning but didn't work. 1 pad was always farther out then the other. I just repositioned the caliper to center the rotor. Solved the problem.