Am I going in the right direction?

Hi Scotty,

you answered a question a few weeks ago about a spongy brake pedal, citing the second hand replacement master cylinder as the likely cause of the issue. I still persisted, bleeding the system many times, going through ~3litres of fluid, and the pedal is definitely firming up, but I feel like i'm missing something, the pedal still travels about 40% before brakes engage, and firm up nice after a few pumps.

so i came up with a plan... using some old brake line i welded the ends to make blanking plugs. first I plugged the master cylinder, to test internal leaks and the pedal was solid, no give, so I've ruled that as working. next I plugged the ABS pump where it goes OUT to the rear brakes. again the pedal was completely firm, to me this indicates the rear portion of the system is at fault.

so my question is, do you think this process of fault finding is ok? or by blocking lines am I giving myself false results?

The next thing to do is to block the various ports of the rear junction box, to hopefully narrow it down to a single corner. but how come this method isn't mentioned in any brake diagnosis threads I've read? it seems really simple and easy at finding the root cause when there no visible sign of air or leaks?

Thank you