Rear brake was dragging on the way home the other day so it was time to get serious and find out whats going on. Ended up removing the rear brake caliper and the brake pump. There was no scoring or any marks on either parts but some rust on the brake pumps circlip ring.
I should have removed the rear wheel as you have to literally take the caliper apart into two pieces to get it past the rear belt sprocket. If the rear wheel is one you need to disassemble the rear caliper if not you can most work while the thing is on the bike.
The rear caliper is bolted to the swingarm with 2 6mm hex bolts. The brake hose is a 6mm hex as well. Break loose the brake caliper hose but do not remove it, then loosen up the 2 bolts that are holding the caliper to the swingarm. Remove the small clip that holds the rear brake pad bolt and then a small nail to push the bolt out.
Pull the caliper upward and remove the pads and disconnect the caliper brake hose. Now pull the caliper apart. There are 2 rubber boots that are connected to the other side of the caliper once they are pulled apart the caliper can be removed in two pieces.
Use compressed air to slowly push the calipers piston out of the housing by using the now empty brake hose slot. The piston will come out with force depending on how much pressure you created. remove the bleeding screw and clean everything with brake cleaner. Inspect the piston and seal for any scoring or tears. Reassemble that part of the caliper back together
The two pieces of the rear caliper
Clean up the sliding area is there is any rust and use brake caliper grease on the metal sliders and also pack some into the rubber seals
The rear pads were still within the wear limit of >1mm but were replaced as well.
Put the caliper back together and see if everything works together and the sliders work. Then install the caliper back onto the rear wheel and connect everything that was disconnected
Brake pump is pretty easy to disassemble. Unbolt the top brake line that goes to the abs unit and the rubber hose coming from the reservoir. Unclip the bottom that connects to the brake lever and remove
As you can see there is some corrosion on the circlip so make sure you clean that off before further disassembly.
Once you have the circuit clip removed the pump should slowly come apart, you can use compressed air again to get the piston to come out. Once its out you can see all the parts. Clean everything and check for any signs of damage: scoring, torn seals, brittle rubber.
Be sure to inspect the spring as well
Clean out the bottom of the "piston pusher" and remove any rust that might have collected in there.
Clean the pusher and remove any rust from that as well. Grease up the rubber seal and reassemble everything.
You will have to bleed the abs system and may even have to go out for a ride and have the abs engage in order to "cycle" the abs pump. I ended up bleeding my brakes three times before everything worked the way it should.