No brake pads! The pistons have been acting directly on the rotor... without marking it. Wow! Pistons are pushed way out and at an angle as well.
Measure a piston and order pads and pistons for overnight delivery from my supplier in Qld. Now to manufacture the missing retaining pin (red arrow). I initially planned to use a button head, but decided I could use a socket head more easily...
Socket head in lathe chuck with centre at other end... part way through machining, correct size just leaves thread marks, but should be fine as it ends up feeling smooth enough...
Tested and cut to length..
Done and fitted with a spring washer...
Bleed valve was rounded off and had to be removed with a lockjaw pliers. Replaced it with a new one and popped out the pistons with air. First piston was easy then the air blew out through through the port to the second piston. Caliper then pulled apart and air used to get one piston easily out of of the second half. I ended up using some rag forced into the ports with my finger to finally push out the remaining pistons. Luckily the cylinders and pistons were nice and clean or we would have had some more mucking around...
Here is one of the worn pistons...
New pistons, kits and pads arrived and all is well...
But just for interest, here is one of two CB750F calipers we did the same week. Illustrating why it is a good idea to change your fluid every couple of years and pull calipers apart for a clean at the same time. You don't need a rubber kit as most o rings seem to last years...
The pistons were fine as were the cylinders, but we did throw in some new o rings and give everything a good clean as, it must have been a long time since these had been done. Also the calipers were initially pulled apart because the brakes were jamming. This would have been because of the sludge and a slight build up on the pistons (removed with steel wool) and also possibly the square o rings not pulling the pistons back away from the disc when the brake lever was released.