The rear piston needs wound in as you push it back as it's threaded


p.s. Brakes are easy to do if you know what your doing, but something that shouldn't be fucked about with if you don't, it could be the difference between life & death (yours or someone elses), sounds overly cautious but it's not unknown to happen!

Tips to make your life easier:

wire brush nut heads to remove dirt/rust. spray with WD, leave for ten mins before removing.

wire brush caliper carrier where pad's move back and forth or clean/replace shims if they are present (should be on a sub?) also copper grease where the pad contacts.

copper grease back of pad where piston touches, not loads just a thin layer.

remove sliding pins from caliper carrier (they may come out easy, they may be jammed, but they should slide easily) (where caliper bolt, bolt's onto, has a rubber boot, just give it a tug and it should come off, bit of wet and dry with some WD to clean the crap off and re-copper grease and refit, making sure rubber boot is seated back onto carrier properly)

piston needs pushed back in as said, and turned clockwise at the same time, there is a tool to make life easy but a big pair of adjustable mole grips and some carefull piston seal dodging, they can be wound back in a turn/pushed/wound back in a turn/pushed etc etc until they look home.

My advice to you would be to get the torque settings for all the bolts, and use a torque wrench. As a novice (no offence) you won't have the 'feel' for how tight a bolt 'should' be (comes with experience ) and may end up snapping a bolt/pulling threads out or not tightening it enough.


HTH.