Just bought my new xt brakes and had to trim the hose.
All ok but pumped the brake without the pads in place - now one piston won't go back in (wheel side). There must be an easy solution but I'm buffered if I can work it out.
Please help as desperate to ride today 🙁
Take the pads out and gently try and lever the piston back in with a tyre lever / screw driver or something (best to use a non-metallic item but if you're desperate a screw driver will suffice).
The piston should go in easily without using alot of force. If it appears stuck then it try taking the top off the reservoir cap at the lever end and try pushing the piston in again.
If you had bled the brakes with the pads left in then the pistons won't be reset properly and you'll have too much brake fluid in the system. When you bleed the brakes you need to put a 10mm allen key in between the pistons (assuming this may be the problem).
I'm no expert,so don't take serious notice of this, but I don't think there's any reason why you can't push the pad back with a soft tool like a tyre lever. After all, that's what you would have to do to fit a new pair of pads. Did you cut the hose, refit a new olive and insert and re-connect the hose at the lever end without re-bleeding? I will have to do this soon as I've bought opposite handed brakes from Germany. Did it go ok without re-bleeding? I guess you won't know until you've ridden with them.
Thanks - there are no pads in and the reservoir cap is off but the piston won't go back in and I have snapped a tyre lever trying ......
HAve you got the reservoir caps off or bleed open?
Has the piston been pushed out of the caliper too far? How much of the piston is exposed?
Also are they 2nd hand or new?
There is about 2 maybe 3 mm showing but they were further than that which makes me think I pushed it out too far before I reset the pads.
The reason for suggesting taking the reservoir cap off is that I once tried to bleed the brakes during a race with the pads left in the brakes and quickly realised that the pistons needed to be fully reset and by taking the reservoir top off I reset the pistons and saw the brake fluid rise is in the reservoir.
That's sounds ok. If my pads are worn down I can get 2-3mm showing.
Try something like a wrong end of an external bottom bracket spanner. It's flat, chunky and just the right size. Try to use a bit of force (but not too much) and see if that makes any difference.
New brakes - cap open - won't budge.....
I'm out of suggestions other than to push the pistons out to around 5mm and lube the sides of the piston with brake fluid and try again.
I've got old Shimano XT calipers and occasionally the pistons may pop out enough for the brake fluid to leak out from the pistons but I've always managed to get it back in.
Maybe the seals have become dislodged somehow.
Sounds like the piston has jammed in at an angle when you tried to push it back in. Pump the pistons back out. Try and hold the non jammed piston in place so only the jammed one moves. Then try and push the piston back in, whilst keeping it square in the bore.
sounds to me like you've pushed the piston to far out,
theres a little rubber ring about 3/4 of the way down the piston,
if you pump the brake piston to far out without brake pads in this ring becomes unseated and will not go back in straight,
when you re-bleed your brake, it will leak.
Shimano do not carry this ring as a spare part and in means a new calliper
I found all this out the hard way, like you i pumped the brake with no pads in.