Thanks Thomas, after the assessment at the shop, I'll be sure and return comment on the fix. Appreciate all your excellent education.

 

After a reread of some of the earlier posts where removal of the vacuum with the engine running gave a firm pedal again. Could there be something wrong with the power brake booster? Not sure what that could be.

 

Shark

I think I correctly tested the booster

1. Holds vacuum for extended period via hand pump and after motor is turned off
2. I can hear the vacuum release when clamping the vacuum line and removing the check valve
3. Check valve operates as expected
4. No leakage from MC detected
5. Pedal slightly drops when motor is turned on (then I can push it straight to the floor)

my expectation from above is that it is functioning correctly?

 

With the engine off, try pressing the brake very hard. I am thinking that if it's not the booster and the calipers aren't leaking and there's no air in the system, then it might just be the master cylinder.

 

initially I also thought I could have an internal leak in the MC, so I have since replaced the old MC with a new one (after a proper bench bleed)

with the engine off, I have a firm brake (feels normal) and I must put a bit of pressure on it to get it to bottom out. Plenty of return on the pedal as well

start the engine, I can feel the pedal drop, and then slight additional pressure, the pedal goes to the floor. As I take off the pressure, the pedal comes back up to normal position.

I've placed cardboard under the complete vehicle to check if there is a static leak somewhere that I haven't noticed

is it possible that I installed an incorrect proportioning valve? See attached

I noted that the new pv4 does not have a reset button

 

I have got to admit this one has me puzzled. With a good blead brake system you should not be able to press the brake pedal to the floor with booster or no booster its hydraulically impossible. I can't see how a bad proportion would not allow the pedal to go to the floor, unless there was a leak. I will admit this is a good one.

 

There is another senaro that the master cylinder is bad. And the replacement is also bad. It's failing when extreme pressure is applied. It's rare that a replacement is bad but not impossible.

 

thanks Thomas

is there a way to bench test the MC?

also what should the expected bleeder value pressure be in a working system

 

You can bench test if you have a way to clamp it down when you do it. I think it would be easier to test it on the car bolted on. The normal pressures are around 800 psi normal braking range. 2000 psi maximum range.

 

can you advise me the test method for the MC?

800psi to max 2000psi at the bleeder valve, correct?