Brake issues

[Toyotafan78]

Entirely brand new braking system in my rail.
Cnc 3/4 bore master cylinder
10lb residual pressure valve
All new steel hard lines
All new braided flex lines
Proportion valve to rear
Cnc cutter brake
All 4 brand new german wheel cylinders.
All 4 drums adjusted properly,stops great if the pedal is there.
Have tried every method of bleeding (manual,pressure,vaccum,even gravity,bench bled master cyl.)pedal pumps up hard,but if it sits more than a couple seconds it goes right to the floor,3-5 pumps it's back solid, can just stand on it for as long as you want,doesn't drop a bit. As soon as you let off it,and hit it again,right back to the floor.
No leaks anywhere,have cracked every connection loose looking for maybe a cracked flare or SOMETHING that explains wtf is the problem.
Does anyone have any idea what is wrong,I'm at my wits end, absolutely fed up with the thing. Been fighting with it for 2 weeks,haven't gotten anywhere other than growing a bitter hatred towards it at this point.

[raygreenwood]

Classic symptom ....bad mastsr cylinder seals.

Was this MC by any chance sitting around on a shelf for long periods of time? What is happening is that the seals are stiff and have shrunk a bit. You pump them up and hold pedal pressure and they are inflated and seal
Let off for an instant and they retract and the pedal drops.....no pressure.

Common problem with high shelf life MC's.....and NOS cylinders over about 5 years old.....which are all junk. Occasionally it can be crap in the compensation port valves....but thats rare. It can also happen rarely when the cylinder has been honed ro large. You should never hone brake MCs anyway. Ray

[Toyotafan78]

I've been leaning towards the fact I just got a bad Master, it wasn't in stock at my local supplier,but I guess that doesn't mean it didn't sit on the shelf at cnc for years.
It's a brand new one,never rebuilt. I won't install used brake parts.

[Q-Dog]

Possible the brake shoes aren't adjusted tight enough. Tighten all 8 shoes for a good bit of drag and see what happens.
_________________
Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[Toyotafan78]

Even tight against the drums it does it. Going to try a different M/C,see if it makes a difference.
Thank you guys by the way...

[Toyotafan78]

Got me some brakes finally!! Not only bad master,3/4" bore that the local buggy shop sold me was not pushing enough volume for the application. Picked up a 1" bore wilwood master for a whopping $53,got good solid brakes now. I am super stoked!!

[raygreenwood]