Front Pads Binding

[ratkinsonuk]

I changed my front pads recently, but accidentally popped one of the pistons out of the caliper whilst cleaning. I've bled the brakes and they're working fine, but the pistons refuse to retract and the pads are binding, so the wheel won't rotate freely.

I've come back from a 2000 mile European trip expecting it to have sorted itself, but no joy.

Any ideas what I can do to get the calipers to release?

Cheers

[unfazed]

Take them apart and clean them, sounds like a seal binding, you might have to replace the seals.

[agricola]

Just to clarify, you rode the bikes for 2000 miles with the brakes binding? Just be aware, there is always an amount of drag present, the front wheel will not rotate endlessly when spun by hand, pistons do not retract all the way back to the bottom of their stroke. Check youve not too much fluid in the master cylinder. With the cylinder cap off, you should be able to push the pistons back fully if there working ok. Just watch for fluid spilling out of the reservoir

[ratkinsonuk]

The amount of bind equates to about 20mph off the top end, Agricola, so it's not just natural pressure.

From what I read last night, I'm inclined to think Unfazed is on the right track. Not looking forward to taking the calipers apart and having to bleed them afterwards, but I think it's where I'll have to start the hunt.

The reservoir is actually quite dry, which I assume is due to unbled air making it's way up the brake lines. The alternative is a small leak on the piston that popped out, which I think can also cause binding issues.

It's annoying, because the brakes work fine apart from this issue 

[ratkinsonuk]

Took some pictures last night.....







Do you think this could be enough to stop the pad sliding?  Looks like only one side is sticking.

[Grahamm]

Took some pictures last night.....

No pictures to be seen and just putting the link into the browser gives a 403 error

[ratkinsonuk]

Photo 1

[ratkinsonuk]

Photo 2

[ratkinsonuk]

Photo 3

[BBROWN1664]

I would be tempted to put new pistons and seals in. At the very least clean those ones up as well as you can and put new seals in.

[ratkinsonuk]

The pistons are moving freely at the moment. I'm able to easily push them in with one finger and the reservoir cap on.

I'm not ignoring your advice, and was going to try changing the seals as the next step (cheaper than £700 worth of calipers), but can you explain the mechanics behind it. How can leaking seals cause the pistons to stay out and the pads to bind?

I read on another post that the pistons don't automatically retract, but are pushed back by tiny movements in the disc against the pads. There will always be a small amount of contact on the disc because of this. If this is true, changing the seals would only help with breaking issues, and not releasing the breaks/pads afterwards?

[ratkinsonuk]

Just as an aside, a full piston kit (8 pistons and 16 rings) is over £140 from Fowlers!

[BBROWN1664]

if the seal is not in properly, it can bind on the side of the piston.
With the amount of crap on the pistons in the picture, its quite possible the seal is damaged and binding.

[ratkinsonuk]

As I was saying, the seals appear to move in and out fairly easily. The amount of dust on the seals in the picture is down to 2000 miles riding in one week with the pads rubbing the disc. Prior to my trip, I replaced the pads and gave the calipers and pistons a good clean. There was no sign of any marks on the pistons at that point, but I'd admit I can't be 100% sure as I only remove one piston (accidentally).

At the moment, I'm inclined to think it's down to the grooves in the calipers caused by the pads, but don't know how I'd go about flattening them again.

[BBROWN1664]

Looking at the shape of the grooves, the problem woul dbe the pads not getting to the disk rather than retracting.
Pads don't actually retract though, you just remove the pressure pushing them against the disk so I doubt its that.

Do all the pistons pump out smoothly and push back smoothly? By that I mean with similar amounts of force? If not, the one that's harder to push is where to start looking.

[agricola]

On the last picture posted, there is a groove in the inside face of the left side of the caliper, that shouldnt be there, have you checked the discs? You also should check that the bobbins are free to rotate within the discs. Whatever size hole is in the bobbins, fit a screw with a nut on the back and nip them up on the bobbin. Then spanner the screw round while spraying in some brake cleaner.

Might also be that he pads are jamming in the caliper even though the pistons are returning. Check the brake pins/guides.

Failing that, full overhaul of the calipers. Not much difference in the end result of either riding around with brakes dragging and risk of locking up, or failing to apply when reqd