I have a Shimano calliper problem and I haven’t much experience with them as I’ve always been a Hope man.

We have a BR-RS805 calliper that I’ve been really struggling with trying to stop rotor drag, this is the road brake for anyone not familiar.  The brake is only a couple of months old.

I took the pads out this morning as one of the pistons looked a bit lazy, and one side just won’t retract.  I’ve taken it off and even without oil pressure in it, and with mechanical assistance (pad spreader tool) it still won’t retract.  Is this a blown seal do we think?  If so, is it repairable or is it a return for warranty job?  It has good lever pressure prior to being removed, and didn’t appear to leak.

Thanks for any help offered.

No one??

Best to push pistons home with pads in place. Seal sounds fine if not leaking. Piston probably squint and binding in seal. Should be fixable.

Spread the pistons whilst loosening the bleed screw to allow the piston to retract then tighten the bleed screw.

Sillyoldman – Tried several times with pads in place, but nothing doing, wasn’t moving.  without pads, like you say the piston is def squint, can I crack the body in half to get at the piston easier?

Soma – Yeah, tried that for a start, one piston still doesn’t retract.

Warranty, shimano calipers arent the best atm

Seeing as you need to bleed it anyway, I’d strip the caliper down and blow the piston out with compressed air. Split the caliper in half and wrap in a rag to catch the bits, block the transfer port between the two half-calipers with your finger, then push the nozzle of an air gun (or CO2 inflator) into either the bleed port or where the hose connects and give a quick blast of compressed air. This will blow the piston out. Clean the caliper in hot soapy water then rinse again in clean boiling water and let it dry. Lube the seals and pistons with a smear of brake fluid and reassemble.

Sounds like the seal has twisted, either strip down and replace seal or warranty them

If they are under warranty just warranty them, if you start screwing around you won’t have a warranty if anything goes else goes wrong.

Whilst under warranty technically due to age, I bought them new from eBay so not, unless I ask the friendly local shop to slide in through.  In the meantime I’ve bought another caliper for £30 with pads and fittings, so not stuck.

Thanks all.

Found the problem!  Split the caliper and popped the piston and found the back of the piston broken off and quite a bit of ceramic debris in the back, that’ll explain why they didn’t want to retract!  guess you can’t get replacement pistons? so good job I ordered another caliper.