Do you still have the old master cylinder? If so, wing it in place, bleed the brakes and try again....

So I had her test the pedal feel and how well it held pressure.

She said that once she had pressure it would hold pack on her foot for about 30 seconds but then it woudl slowly, very slowly, start to feel like a balloon losing air.  She repeated a few times.  Same results. Pressure for about 30-45 seconds and thenafter about 3 or 4 minutes at the floor.

I had her look at the master cylinder lid and she noticed a very very small amount of fluid.  She wiped it up, repeated the test and again, there was a very very small amount of fluid on top.  After i was done bleeding I screwed that thing on VERY VERY TIGHT.  It is a white plastic cap.  It didn't have a washer on it, but perhaps it doesn't need one.  How tight does it need to be?  Should i try using plyers to get it even tighter?

At the begining of this we did the price comparison and decided to do drums to save on costs and to stay "original".  We also figured our stock engine didn't need more than drums.  I didn't realize that sticking with drums would lead to 3 months of headaches.  But on the flip side I have learned a TON about brakes and that was always part of the owning a classic car.

As this problem occurs after using the brakes a few times itt seems to me if you think the adjusters are loosening up you could use a woodworking clamp or a vey large hose clamp on the shoes and have the wifey mash the brakes a few time while looking at what is happening in your garage.

Are your ready for disc brakes yet ?

Yes, we were mostly doing that to check that the springs and cylinders would move as expected.  

Next time you have your wife checking the pedal travel....you need to have the drum on...and she should use the foot not the hand.
Without the drum on.....of course pedal willl go to the floor.

LOL ,  at least that part is working :-)

I've used hose clamps to isolate the rears from the rest of the system, the symptons remain.  The rear hoses "look" new'ish.   The front hoses are new.  Here is the list of parts so far

• 1 x Gasket, Thermostat Housing, Paper (GTG0101)
• 1 x CV Boot, 850-998cc, Unipart (GDG0233)
• 2 x Brake Hose, front, drum brakes (GBH0170E)
• 2 x Brake Drum, Standard Front (GDB0105)
• 2 x Brake line, front wheel cylinders (SPA10)
• 1 x Wheel Cylinder, 3/4" (GWC1102)
• 1 x Thermostat, 167°F (GTS0102)
• 1 x Brake Assembly Set, Twin Leading Shoe (SBR0075)
• 2 x Brake Drum, Standard Rear
• 1 x Master Cylinder
• 75 Gallons of brake fluid.

You can dot punch around the adjuster but it's not a very satisfactory solution particularly on a new part. Replacement would be best if that does turn out to be the problem. As you suggest, if the adjuster has moved then turning it back to the correct position should restore the pedal to its correct position. 

I will double check tonight, but i am 95% sure that once i have good pedal feel there is no drop at all at the pedal.  I will have my wife confirm tonight.

As for the adjusters being loose, is there a fix for that besides replacing the backplates?  I guess i can confirm it by adjusting, then pumping the brakes to similuate stopping situations while in the garage, then re-inspecting.  To replace the backplates i will ahve to disasemmble nearly everything and reinstall them on the new plates, right?  Then rebleed and readjust.  (Sounds like a good time to replace my brake light switch (Accel 181101) if i am re-bleeding the whole system)

Malsal's suggestion above will determine if the master cylinder is faulty. The pedal should maintain pressure. If it sinks to the floor the master cylinder is faulty or there is a leak somewhere. Reading your posts it does not sound like you have a leak and having a good pedal after bleeding and adjusting suggests that there is no longer air in the system. This is why I'm wondering if the adjuster is backing the off. Have you checked the suspect corner to see if this is the case. If it is I would contact the supplier of your backplates and request a replacement. 

If you sit in the car stationary and hold a steady pressure on the brake pedal does the pedal stay firm or does it slowly go down towards the floor ?

I was thinking that this could be the case as well.  When i adjust to wheel lock it only takes a very small nudge backwards to get the wheel to spin and it feels pretty loose.  How do i check/adjust/fix that?  The backing plates are new on the fronts.

First, check the position of the lines in the master cylinder are not reversed, the second 100% recommend synthetic brake fluid leaves no air in the lines, the third bleeds first master cylinder, then the cylinder farthest to the nearest to master cylinder.

I'm wondering if one of the front adjusters is lose and backing off as the shoe pushes against the drum?

no???

Is Robster helping you? Maybe he moved the solenoid so it shorts out on a brake line and boils the fluid at that spot.

I'm not sure about if I bleed/adjust and leave it for a few hours how the pedal would feel.  I've always just done the bleed/adjust and then go drive.

I'm not sure about the master cylinder weeping, but whenever i have taking to cap off to start bleeding the fluid is always at or nearly to the top of the cap.

Today i only bled the front two wheels (left side than right side).  I've already done the back several times before,

Let me get this straight. You bled the system with a pressure bleeder; cool, and I am jealous and I won't even call you spoiled; and the pedal felt fine after that. At this point you have all four corners assembled and adjusted according to the shop manual. There are no leaks, kinks, smashed areas of lines, etc. The master cylinder is not weeping fluid down the pedal arm. While in the garage you can leave the car and come back to it again and again and the pedal feels fine, but the moment you actually drive the car and use the brakes something changes and the brake pedal goes away?

Yes, master cylinder was replaced when the car was originally being looked at by the mechanic.  It is the Cooper S size bean can.

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