bigger master cylinder?

[trevorbrady]

I fitted a rear disk brake conversion to my bug this weekend, with Porsche 914 disks and Peugeot 504 calipers (no, I don't know why the manufacturer chose this caliper either )
I had everything bolted on, plumbed in, adjusted and bled only to find that the stock VW master cylinder can't move enough fluid to have much of an effect on the rear pistons. The result is very soft spongy brakes, and the pedal hitting the floor with very little effort.

Is there any other master cylinder that will bolt in place of the beetle one but have a larger capacity?
I'm thinking of ditching the 504 calipers and sourcing some Golf ones or something. I've already discovered getting parts for the 504 calipers is a bloody nightmare...

BTW, I ended up switching back to the rear drums, cos I had to drive the bug and just don't like the idea of having no brakes!!