Many thanks for your excellent guide.
I had one very stuck piston on my Gen 4.
In step 7 you indicate how to even up and ease out the pistons using the brake lever. I had to get them much farther out in order to remove them without damaging them.
I made use of the 8mm spanner that I was using for the bleed nipple. It’s much thinner than my micrometer box.
Given the pressure I had to apply to shift the stuck piston, I suspect the good piston would have crushed anything plastic that I could have stuck in there.
After some experimentation I discovered that laying the spanner shaft flat across the calliper opening and pumping the handle pushed the free piston almost all the way out. Then it jammed on the spanner but still retained pressure. Maybe it was only sat on the dust seal, but it worked.
Keep pumping the handle hard and the second piston will eventually move to the same point.
Now with them both being stuck so far out I could slide out the spanner and the pistons could then be wiggled from side to side and easily pulled free.
That tip from TheStig about the closed brake lever is working nicely to avoid the system draining down.
