Shimano sticky piston

aidso

I've a set of Shimano deore hydraulic brakes and the rear wont bite. I've a few set of pads in it and when I pull the lever it does all the way to the handlebar. I've taken the pads out and pushed the pistons back and notice when I pull the trigger the pistons (both) only move about 1mm inward.
Things I've tried:

Push back pistons and pull trigger x 100; Submerge in hot water and scrub pistons with small brush; Rub a little bit of chain lube around pistons, wash and pump;

What's next on the list?

The Rookie

If they move, how are they sticky?

Sounds like the system is underfilled and you don't have enough fluid to allow for the extra required with the pistons out with the pads touching the disc.

The above methods seem a sure fire way to create issues in the future, clean and lube with the fluid they are designed to come in to contact with, namely mineral oil.

aidso

The Rookie wrote:

If they move, how are they sticky?

Sounds like the system is underfilled and you don't have enough fluid to allow for the extra required with the pistons out with the pads touching the disc.

I was hoping for something like this. I have run my hand along the cable to see if there were any cuts/tares that oil could be leaking from but didn't find anything. Can it evaporate? And is it a case of me just topping her up or should a full bleed be done instead.

The Rookie

The process for bleeding is the same as filling up......

No it can't evaporate its a sealed system.

I'd be sure to clean round the pistons with some mineral oil, make sure you remove any excess!