semi hydraulic sip disc

[MCH]

I have got a rear semi hydraulic disc, besides it being a bugger to fit,

im now at the part where im trying to get it to work, spent the whole day frigging squeezing the lever and the pistons in the caliper just wont move, i pushed them in to see if there was movement so they do work,

iv bled the system over and over and still it wont work,

so i went by process of elimination, took the semi mast cylinder to bits and checked the seals, they seem fine, put my finger over the hole and pumped it and it creates a push ,
tried a different caliper and still no movement,

fluid is being pumped into the caliper but there is just no movement in the pistons on either caliper i have tried,

lost the will to live today with it, so going to take it to a shop tomorrow see if they can sort it, iv checked the seals in the calipers too and they are fine,

so anyone got any ideas why the bloody thing won't work????

[wack 63]

Remove the caliper and fit something between the pads to stop the pistons popping out ,then hold the caliper so the bleed nipple is vertical and higher than the pistons as when you've tried to bleed it the fluid has bypassed the pistons and headed straight out the valve.The hose may also have an air lock where it curves above the master cylinder so you could try removing it from the frame ,tilt it whilst pumping the lever to force the air out. Failing that try reverse bleeding the system .

[warts]

If you are still have difficulties after trying Wack's system above, and you could try leaving the caliper raised overnight, just to let the air float to the top.
My Guzzi has linked front/rear brakes. The link pipe is about twice as long as what can be seen in your pic. The master cylinder just couldn't move enough fluid to fill the pipe.
I bought a Gunson EziBleeder , which uses air from a tyre to force fluid through the system under pressure. Purges them little bubbles right out. One of the best gadgets I ever bought. Absolutely brilliant. Only downer is you need a cap for your master cyl that you can drill for an adaptor.
http://www.gunson.co.uk/item.aspx?cat=664&item=1818
They are a hobbyist version of the sort of thing used on the line when I was an apprentice, they were operated by std air line pressure, in case anyone thinks there's a risk to their brake lines or cylinder seals.

[MCH]

update:

i took it off and lifted the caliper higher than the master cylinder and bled it again, this time it worked and i got movement in the caliper pistons, however more on one side than the other, anyway i bled it a few times and the pistons were moving,

fitted it back on the scoot and wired it all back up and then rolled down the drive, put my foot down on the brake pedal and the brake is just really weak,

i can hear the pads making contact with the disc but it just isnt putting enough pressure on to make me come to a stop,

whats next? bleed the system again?

or sack it off and look to go fully hydraulic?

[wack 63]

One of the main problems will be flexing of the components ,ie the tie bar etc. The cable needs to be thick gauge and same with the outer as you will have to take up the "slack" before the hydraulics start to work.

[ArmandTanzarian]

Have you tried filling it up from the bottom using a syringe and a rubber pipe on the bleed nipple?