hello all, I have stripped the front hydraulic brake and it was in a very sorry state after 20+ years of neglect. I cannot get the caliper pistons out, I’m sure recently someone on here had the same issue but I could not find the thread. So what is the best way of getting them out?
Also can I test the hydraulic brake light switch without hydraulic pressure?
I have found these two posts on an earlier thread
Well I had a bearing extractor kit under the workbench and its worked a treat!
Now to clean everything and get the seals ordered. Good news, at some stage I replaced the pistons and they are fine and will be reused. 
I used compressed air and nearly took the side of the shed out. I now wrap a towel around a few times which restrains the piston as it pops out but be careful and point it away from you and anything you hold dear . Just put the air gun in the bleed valve hole and give a short squeeze.
Guzziology says not to use compressed air, I assume this is so brake fluid is not sprayed around not because the pistons get ejected at speed!
I have used a tyre foot pump, it worked but destroyed the pump (> 100 psi 
).
Another technique I saw lately, assemble with new fluid, and pump the brake lever / pedal to push them out. (?)
Back in the day I had a Yamaha FZ750. A wonderful bike but fitted with calipers that would seize at the first mention of winter/rain/dirt/salt. I got quite good at cleaning, refitting and bleeding them as it was my only form of transport and commuting to work.
When the pistons were at their worst the only reliable way of getting them out was to use a large grease gun connected to the bleed nipple. A grease gun can generate a terrific amount of pressure to force the pistons out, but in a controlled manner. The grease takes a bit of work to get out afterwards, but it was still quicker than the alternatives and didn’t damage the pistons which I often cleaned/polished and re-used.
All good solutions thank you, my bike has been off the road for over 20 years (probably 25 years!) and the front calipers, splitter and handlebar reservoir had never been disconnected. There was a very small amount of brake fluid remaining in the system but only a few drops and the master cylinder was seized so no way to put any pressure through the system.
I like the idea of using compressed air or a grease gun but as I will have to clean the galleries of the calipers anyway I don’t think adding more stuff that I have to remove later would be beneficial. Maybe filling a grease gun with brake fluid might work?
Anyway that is academic as the bearing puller worked brilliantly, there are no marks where the puller grabbed the pistons and even if there were it is in a non critical area as it is the outside that needs to be smooth not the inside.
I need to go shopping now for seals and crush washers.
Watch out for the replacement seal kits, someone I know bought some replacement kits and the small O ring that seals the holes between the 2 halves of the calipers were oversized.
Second tip, I recently bought a master cylinder kit for my California and Ducati Paddy had stock when Gutsibits were unavailable and he was cheaper than Gutsibits.
Just to mention (afterthought), re brake fluid or pistons flying about if using compressed air (tyre pump) etc., don’t remember any fluid ‘spillage’ as such, mind you I was working outside, as that was the only available free space to work in (still is, really!), pistons probably wrapped up in rag, came out with a loud pop. 
