Disc brake suddenly locked up

[JulianHJ]

I have a 2010(?) Cube Ltd Race with Formula RX hydraulic brakes. I used my bike for the first time in a few months this morning. I checked everything over before setting off - all good. I rode a mile or so to my LBS, then on for another mile or so in to town. After a quick errand at the bank (took the bike in with me) I noticed the rear wheel was locked up. I went outside, had a closer look and the brakes were almost fully on. I tried the lever and it was extended at it's normal position; there was very little movement as the pads were already touching the disc.

I got the bike home (took the rear caliper off to get back) and had a Google. I took the pads out, checked that the lever was moving both pistons (it appeared to be), then eased the pistons back with a screwdriver. I didn't use too much pressure, as I didn't want to cause any damage. I put the pads back in and the pistons have only retracted as far as shown in the photo. The disc is a little thicker than that gap, so the pads need to be about twice as far apart I'd guess.



Am I not using enough pressure to push the pistons back? Is there a fault elsewhere? I'm assuming that something has gone wrong somewhere for the pistons to suddenly fail to release.

Can anyone point me in the right direction in terms of a DIY fix, or is this a job for the chaps at my LBS?

[neenaw]

It's difficult to tell from the picture but it looks like there's some corrosion on the pistons.

Try removing the pads then pump the lever so the pistons come out about 5-6mm each. Check the surface of the pistons and see if there's any corrosion or gunk on them that may be stopping them from retracting.
If there is, give them a clean up and push them back in. If there's light corrosion on the pistons you should be able to clean them up with some wire wool or fine emery cloth and a bit of brake cleaner.

[JulianHJ]

Thanks, I'll have a look at that.

[anonymous-user]

I'd guess its air in the system, check the seals at the lever end. The formula rx brakes on my commencal were shocking...

[Lawbags]

Either air or water.

[Watchman]

From new my brakes were binding and I never got to the bottom of it until I wrote out the problem on PH a few weeks back, at which point I worked through the problem. It seems to me that my brakes were bled while they were off the bike, and too much hydraulic fluid was used, leaving the pads with not enough movement to retract fully into the calipers. When the brakes were mounted on the bike they always dragged, and as they heated up, they tended to lock.

I got around it originally by adjusting the lever further outward but there simply wasn't enough adjustment available to afford the pads complete retraction.

Squeezed a little fluid out of the bleed hole and - ta daaa - they're perfect for the first time in the two years I've had the bike.

[Gren]

My missus has a LTD Race with the same brakes. Every time I change the pads I have to really push hard (lever with a screwdriver with the pads still in) to get the pistons to go back far enough for new pads not to rub. To the point that I think somethings going to break. Other than that and a bit of noise they've been great though.

Answers on your BikeRadar post seem to have it covered as well

Edited by Gren on Thursday 12th December 08:52