Anyone encountered this brake problem on a MK1 Capri.
New everything, booster, master cylinders, re-fuirb calipers, new rear cylinders.
Bled the master cylinder, bled the brakes (absolutely no air) and the pedal is great. Leave it for a short time and when you press the brake it sinks almost to the floor. Stops about 2 inches before bottoming out and is hard as, not spongy. So give the pedal 3-4 quick pumps and it restores it to a good height and is hard, leave it for a few moments and press the pedal sinks again.
Maybe a stuffed new master cylinder????? Any ideas???

Possibly damaged foot valve in master cylinder allowing fluid back into reservoir. Occasionally see this after bleeding brakes where the pedal has little resistance during bleeding and the operator presses the pedal to maximum travel and splits the seal. You get an initial good pedal which slowly sinks down as foot pressure is maintained.
If you have a low level of fluid in the reservoir, hold pressure on the brake pedal and an observer should see a small ripple caused by fluid being returned.
SFE

I get a bit of turbulence in the rear brake fluid reservoir when I pump the pedal. The pedal doesn't slowly sink to the floor when pressed, it has bugger all resistance. It just goes straight down. Almost fees like it is bypassing until almost hitting the floor, then it is very firm, not spongy.?? 

What SFE says is spot on.............if your ok with it, pull master off and strip, making sure NOTHING touches the M/cyl except Brake Fluid or methylated Spirits. Make sure your fingers are perfectly clean or wear gloves. Never re-use old BFluid.
You'll find they left some crap behind during assembly which your eyes may not even see.
Just wash everything with MS and re-assemble with NEW BFluid. Make sure all items are around the right way and work properly. Bleed Master first on bench, then again once installed. If ur careful, the 2nd bleed of Master on car is all you need; you wont have to do the 4 wheels again if you ensure all lines that connect to master are still full(use syringe, or new rubber hose rinsed with Metho if in doubt)
Bernie

A seal with a small leak will slowly fall to the floor while pressure is held on the pedal, a seal that is stuffed will not get pressure.  What you have is neither of those.  Assuming that you did the rear brakes in the correct order, and didn't get any air back in through the nipple threads when bleeding, then my guess is that you have air in the master cylinder.  You can get and hold pressure but once released the bubble expands again and you have no pedal until you pump enough to collapse the bubble.  I would bench bleed again before stripping it.

Removed the master cylinder from the car today, off to get some new seals at the brake shop. Should be back next week. Thanks for all the advice, will follow all the instructions on bleeding after I get it back. Will update you on the result of the master cylinder repairs.

how did you go with the brakes ???
 
sounds similar to what im getting
 
was doing the brake bleeding last night when i noticed a leak thoight it was M/C already ordered new seals but closer inspection was the idiots who made my brake line put the wrong fitting on M/C side  got new fitting ..
put new seals in M/C  but  brake pedal wont hold pressure in it pumps up then hear a hiss between  M/c and booster then pedal just goes down   the only thing i can think it is as i see no leaks or loss of fluid. is the bore is stuffed on master cylinder
wasnt hissing last night but seems to be hissing now and loss of pedal pressure as soon as i hear the hiss
 
anybody had that before ..
 
also i can get hold of a mk2 escort booster and M/C  do you blokes know if they are the same ??
 

The master cylinder I had was new, but when the guys at the brake shop pulled it apart one rubber was folded over and stuffed. They put a new kit in it and I fitted it to the car, bled the brakes and now it seems to hold a pedal. Still very low but I recon that's only the adjustment of the rears. My brake booster makes the same air relief noise when the pedal is pressed when bleeding.