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Last time(only a few weeks ago) I lubed my E4s I noticed that one of the pistons would very easily twist and jam in the caliper while I was pushing it back. Last couple of rides it has started doing it while riding, often enough for it to be a pain in the rear. After any heavy use of the rear brake I feel it start to drag. If a give a little tug on the disc next to the caliper I can feel the piston pop back in with a little click. Is this a known issue and is there a cure? Obviously I will re lube it before riding again.
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Nothing that i'm aware of. Is your caliper perfectly square to the rotor, if it's twisted it'll cause the pistons to cock in their bores. Easy check, if your rotor moves at all when you apply the brakes, it's not aligned correctly and you need to sort it.
Send it to Hope for a service?
I've always found them to be great value for things like this.
Sounds like the piston seal may be compromised. Order and fit a new one. Or send it to Hope for a service.
Sounds like the pads are or have been low allowing the piston to do this.
@coatesy good call, the caliper does look to be slightly misaligned off to the side that would cause the sticky piston to move further than the others. Was sure I had aligned it correctly last time, oh well. Will re lube and realign and see how it goes.
@trail_rat current pads are almost new, don't think I've ever let them get very low but you never know.
I’ve had this. Combination of low pads and old worn discs mean the piston can push out too far.
Having done a full strip and rebuild (reused the seals) and put new pads and rotors in, it seems fine now.
Time to strip the caliper down and look at the piston seal
The seal maybe damaged and the piston could prob do with cleaning
Both of my E4's have done this. The front one last year and the rear is doing it now and due to be sent off for a service at Hope. In my case the front was caused by the piston surface becoming slightly rough in one spot and not allowing the seal to slide, leading to it twisting and binding. Basically the gritty crap I ride through had got under the seal and acted like sandpaper. It's taken over 5 years of constant riding in all weathers for them to do this so I'm not complaining, the front came back from the service like new and has been fine ever since. The rear one just refuses to retract and locks on, new fluid hasn't solved it so it's waiting to be sent off next week. I had an old X2 do the same thing after 6 year's use and a service fixed that too.
Didn't get chance to go ride today but got brake re lubed and re aligned. They seemed to be still well lubed from last time and were moving freely but caliper was definately a bit out of alignment. Watched the Hope video for a recap and pretty sure last time I did them I forgot the final step of centering the pistons so that could have been the issue, when I looked before starting the job I could see the pads were deflecting the rotor to one side. Any way, all seems free now while in the stand will have to wait and see on a longer ride.