I've got a 1983 MK1 Gti, which had been sat undisturbed for 7 years, so I have replaced quite a lot of its components. Regarding the brakes, I have done the following:
New shoes/drums on back
New discs/pads on front
All copper piping replaced
However, the brakes are still absolutely hopeless, I'm pretty much using the gears to slow it down. My old man reckons that it could be the servo, but alternatively as a cheap possible way to find out he says I could replace the 'servo pressure pipe'? Or something similar... any ideas if this might help and if so where to source such a thing?