Disc brakes squealing

[pfm401]

Repair disaster #2 ...

My front disc brake kept "locking on"; I reset pistons and recentred the brakes, but after a while it did it again (x3 or 4 repair attempts!). the brake lever felt really "tight" - no modulation. Not unsafe but annoying and clearly not right.

So I bled the brakes, and tried to lubricate the pistons with brake fluid, pushing them out a bit as per online videos. I think herein lies the problem! the brakes are now squealing, I've tried all the online hacks I can find, sanded pads (a few times) and cleaned rotors. It's ok for a few minutes then the squealing starts again. The modulation now seems ok but the squealing is terrible - presumably contaminated pads.

Should I try to ride for a while to see if it "beds in", will a new set of pads sort it, or is there likely damage to the piston seals from my hacking around that only a new set of brakes will sort out?

Many thanks
Paul.

 

[Cycleops]

You could try riding while holding the brake on, this will get heat into the pads and help bed them in. I've tried this several times with mixed results. Worth a try.

 

[13 rider]

If you've got brake fluid on the pads and rotors that will cause noise . Buy the cheapest of pads and try them and clean the rotors again with alcohol then clean the piston surfaces . Clean clean and clean again . Hopefully then the house goes away and you can invest in better pads . You could try removing more surface layers of your existing pads and througly cleaning them .
Also make sure there's no loose bolts on the calipers and rotors and tight as movement can also cause noise

 

[pfm401]

You could try riding while holding the brake on, this will get heat into the pads and help bed them in. I've tried this several times with mixed results. Worth a try.

I did a version of this keeping the brakes lightly on when going down a long and gentle hill. It seems to have worked! IN any case it wasn't as bad as I first thought, I'd tested the brakes using a "hard lock", when using normal power they only squealed right at the end, but even that seems to have gone!

Thanks for the help

 

[fossyant]

New pads, you'll not cure it by sanding, it will come back. MrsF's fronts would squeel like mad if the bike had been stood, very tiny slight leak from the hose connection (shimano issue), just enough for a tiny amount of contamination. Fixed when connections nipped up, and rotors cleaned.

If you've not got IPA/brake cleaner, give the discs a good scrub with washing up liquid and a light sand of the braking surface with wet and dry. Clean again. Scrub calipers and insert new discs. Re-centre caliper.

 

[Richard A Thackeray]

Recently I had to replace my (Shimano JC04) front pads, as they were contaminated/glazed, & barely offered any braking at all, with a set from 'Discopads'

Compared to Shimano, they're a great price, & work well (used them before)
Out of curiosity, & due to not having any brake-cleaner at the moment, I tried some alloy-wheel cleaner on the removed pads, leaving them soaking for a few minutes
Surprisingly, all of the black/glaze seems to have come off, I'll have to pop them in, & try them

I used this, but I guess others will work just as well

 

[SpokeyDokey]

Recently I had to replace my (Shimano JC04) front pads, as they were contaminated/glazed, & barely offered any braking at all, with a set from 'Discopads'

Compared to Shimano, they're a great price, & work well (used them before)
Out of curiosity, & due to not having any brake-cleaner at the moment, I tried some alloy-wheel cleaner on the removed pads, leaving them soaking for a few minutes
Surprisingly, all of the black/glaze seems to have come off, I'll have to pop them in, & try them

I used this, but I guess others will work just as well


View attachment 688439

Surely not good for sintered pads?

 

[Mike_P]

150-200 grade sandpaper is normally all that is needed to clean pads. Sandpaper on a flat surface and rub the pad across it and around a few times.

 

[Richard A Thackeray]

Surely not good for sintered pads?

What, the wheel-cleaner?

150-200 grade sandpaper is normally all that is needed to clean pads. Sandpaper on a flat surface and rub the pad across it and around a few times.

I tried some wet & dry, but to no avail
Squealing returned within a week

Discs were cleaned with IPA pads, same I use to clean the tow-ball, before hitching BWSOW up

 

[SpokeyDokey]

What, the wheel-cleaner?

I tried some wet & dry, but to no avail
Squealing returned within a week

Discs were cleaned with IPA pads, same I use to clean the tow-ball, before hitching BWSOW up

Yes, the wheel cleaner.

That product is a metal decontaminant and dissolves small particles of metal on eg car paintwork.

I just wondered if it is ok on sintered pads because of this.

 

[Drago]

Stuck the pads in the oven, should remove any contaminants.