Spongy brakes after swapping the line

[J_F]

at this point I'm gonna have to guess the master cylinder is pooched

I went though pretty much the same PITA as you, tricky
on one of my early cars with no power brakes

bled the thing until I was blue in the face, seemed fine
next day, spongy pedal...master cylinder was the culprit

it also was a giant POS of a vehicle
Audi Fox

 

[Mad Mike]

at this point I'm gonna have to guess the master cylinder is pooched

I went though pretty much the same PITA as you, tricky
on one of my early cars with no power brakes

bled the thing until I was blue in the face, seemed fine
next day, spongy pedal...master cylinder was the culprit

it also was a giant POS of a vehicle
Audi Fox

Master cylinders don’t usually give up at the moment you service brakes. If it was working before servicing, it’s probably still working.

Make sure the bleed screw is seating properly. Clean the caliber thoroughly and all connections too. Then pump the lever several times. Look for leaks at every connection.

The bleed sequence is 3 slow squeezes -hold-crack bleeder-close bleeder-release brake lever Repeat. Watch the open reservoir, if you pump too fast you will see a squirt of fluid inside the reservoir.