My son has a 71 Valiant that we converted to manual disc brakes including the following:

1) Swap to 4-piston KH setup
2) Replace metering block with later model having proportioning valve built in.
3) Replace master cylinder with new unit having 15/16" piston
4) Replace pushrod with adjustable unit
5) Bench bleed MS prior to install

The problem is that we cannot get rid of a spongy pedal. We've tried gravity bleeding, normal pedal bleeding, using a pump, etc., but it seems like air is still trapped somewhere.

Suggestions?