No brake pedal return

[Cooper1999]

Evening all,
I'm hoping someone in the forum might be able to point me in the right direction. I'm building a Mini Marcos based on the old classic mini. Now I've got a problem with the brake system which is proving a bit of a problem to diagnose. Thing is the brake pedal no longer has any return - you press it down and it stays there.
The brake linkage looks to move freely up to the servo, the master cylinder doesn't look to be losing any fluid. So I suspect the master cylinder itself. Is this a correct assumption?
The spring which assists with returns the pedal looks to be a little long for this application, but I now don't think this is the root cause - there's no real pressure behind the pedal and as I say, it remains down even when released.
All ideas/suggestions welcome

[Cooper1999]

Thanks all, for the suggestions.
I was hoping for a 'mechanical' problem so looked at the return spring first. Now in this application (mini pedal box/servo etc.) I think the (later model) servo mechanism return spring is a little too long to fully return the spring. However, what I'm finding is the pedal has no return whatsoever - that is, there is tension on the return spring.
I've ordered a replacement spring so that I can play around with modifying the end hooks to effectively make the spring shorter. I've also ordered an early model (mini), non-servo, twin leg pedal return spring (later servo cars were equipped with a single leg pedal spring assisted by the servo mech return spring. This is what I have).

I will look at bleeding the brakes next, but would've thought if there was a leak I would be seeing the master cylinder level going down? I should add, the brakes were working correctly (albeit the car isn't IVA'd/on the road yet).

[Cooper1999]

Okay, so yesterday I tried to bleed the (front) brakes.
On both sides, after a very soft initial showing of fluid after opening the bleed nipple (pedal pressed), further pedal action didn't really show any further fluid being pumped through.
I haven't bled or tried to bleed the rear brakes but am I right in thinking, with a split system, this shouldn't make any difference? That is - if the master cylinder is working properly even if there was air in the rear brakes, depressing the pedal down should show fluid through the front brakes?
(I think I know the answer to this but just want to make sure I'm not suffering a 'senior moment').

So - all signs pointing to the master cylinder, do we think?

Thanks again.

[Cooper1999]

Morning all,
Sorry (again) for the delay in getting back on this topic - work gets in the way during the week, and I've just come back from the British MotoGP where my son's and I were cheering on Valentino Rossi (I was watching Vale win GP before they were born!).

Anyway - to bleed the brakes it was:
1. press pedal
2. open bleed nipple
3. close bleed nipple
4. release pedal
5. repeat
This is the way I've always done it and think it's correct?

So I'll try and bleed the rear brakes this afternoon and see if it makes any difference.
Thanks again and enjoy your sunny Bank Holiday.

[Cooper1999]

So I tried to bleed the rear brakes this past weekend and using the previously described method and the rears seemed to work correctly (as I expect when bleeding). Grabbing hold of the rear drums, with the pedal pressed the drums look to brake (cannot be turned by hand). So it appears it's only the fronts that aren't pressurising.
Does this point towards the master cylinder being defective? Or something else?
Thanks,