Buddy of mine had problems with lkoosing break fluid, so they bought a new master from UK. installed and never could get brake pressure (not really). checked on wheel cylinders and they were wet so changed that.
Fella know has 1968 mustang, powerassisted brakes. Discs front, drums back with proportioning valve.
We couldn't keep pressure (as soon as you released the pedal the pressure was all gone, you can put it straight to metal then).

So we said put the old master back in (bench bled), bled the entire system agin (probably the 10th time). They finished that yesterday. It's better but still the following issues (i won't see it until tonight, so I'm collecting ideas):

- pressure is nearly gone when brakes are not operated for 1 minute
- bleeding they found that when they did the back they couldn't get the pedal to the ground. only halfway). That information is confusing me since they claim liquid came out of the open nipple while they did that.
- they tried with proportioning valve open and closed.

I said they're loosing fluid somewhere, but they state when they step on the pedal the pedal holds it's pressure 100%. even after 1 minute no change (pedal stays in position), but as soon as they release the pedal and wait for a bit the pedal is completely spongy again

I'll go over there tonight to have a look what's happening. Anyone any ideas what else to check or do? apart from trying to bleed it again, clean the whole pipe to check for leaks?

Kalli

 

You need one of those pneumatic bleeders that they use on corvette 4 wheel disc's.

I want to say tha you can rent something similar from autozone or Oreilys but I'm not sure. It's a deal that you fill with brake fluid then add air pressure on top to force the fluid through the lines from the right rear cylinder.

You might even try pressurizing the lines with air too then look for the hissing sounds.

 

we've got a compressor and a bleeder (canister that attaches to it) that 'sucks', but unfortunately none that pushes it. I was always thinking about buying one of those universal ones ... we tried both. normal bleeding (pedal method) and the sucking method

 

Sounds like the same problem I had when I swapped out my front drums for disc. Just a heads up, I'm no expert. I used a pump to "pull" the fluid out. I was having problems keeping the air from getting back into the brake system. It would caused the exact same problem you described. Turned out the seal on my pump was not airtight and air would get back into the system.