I can’t get the pistons on the rear brake to open fully so having trouble getting my wheel in.

Either piston will fully open if I lever it down with a tyre lever, but if I lever each piston open at the same time neither open flush with the block (i.e., all the way). It ‘feels’ like I should be bleeding off some pressure or something to ‘let’ both pistons fully open? Anyone any ideas?

it may have too much fluid in, maybe it was bled without pulling the pistons back first?

I’ve not touched the reservoirs or anything since getting the bike, but the old brake pads were ultra-worn and the pistons closed up quite far.

What pads before and after? I.e. are you going from oem pads to third party pads?

its too much fluid. Open the bleed nipple a crack and then push the pistons back – fluid will squirt out or open whatever port you have for bleeding the brake – lever or caliper end it does not matter

Thx. That sound right.

Well, I opened the bleed nipple up, pushed the pistons in, tightened up the nipple, but now the brake won’t close fully. So I’m guessing too much fluid came out and I’ll need to service them properly?

when you say won’t close fully do you mean the lever pulls to the bars? Might need a few pulls to reset it

Assuming that they were properly set up initially you shouldn’t have done what tj said. As pads wear the pistons move out. Use a big screwdriver and twist between the old pads (not directly on the pistons) slowly for a minute or so to push them both back in and fluid back up into the reservoir.

Given what you have already done you could try pumping the lever furiously until it bites then tying the lever back to tha bars for an hour. Repeat until normal behaviour is achieved. This relies on enough fluid being left in the system to make up for that lost. If not you need to bleed.

Or you’ve just introduced a load of air into the caliper, which will mean a proper bleed.

Don’t use the bleed nipple to drain excess fluid, attach bleed tube or yellow funnel thingy if shimano to the lever or a rag to catch drips if its hope, that way you won’t lose too much fluid to gravity or pressure.

Which brand of brakes are they? Sometimes there are differences in the best way to deal with the problem. I have experienced several sets of Avid brakes which have spontaneously closed on the disk while the bike was stored, and required fluid to be released, but it’s never happened to me with any other brand.

Sorry if that was duff advice – its what it sounded like to me and how I have sorted similar in the past after bleeding the brakes with half worn pads.

Live anywhere near me ( Edinburgh) I’ll have a go at sorting it