I am having brake trouble since replacing a brake caliper on my D*lly. I have bled the system using Gunson Eezibleed. If I now press the brake pedal lightly, it will go down to the floor and no brakes. If I hit the brakes, there appears to be full brakes and the pedal stays firm. I can't see any leaks anywhere. I never had these issues before replacement. Does anyone know how to sort this.

A "sinking" pedal usually means worn one-way valves in the master cylinder's pistons, if by pressing lightly you mean a really slow and gentle push. I think there's no cure for that, except a new master cylinder?
A brake pedal firming up on the second press, with normal foot action, would be air in the system or brake shoes adjusted too far from the drum/drums.

Thanks for that. The MC is only 2 years old. Surely it should last longer than that. I think I'll change it anyway and see how it goes. It seems really strange that there wasn't any issues before I changed the front disc caliper. I only changed it because I couldn't stop it leaking.

You have put the correct brake fluid in? As if it's a D@lly then it must be mineral LMH not normal brake fluid,just a thought as the normal stuff will wreck all the seals. Having made certain that is ok, then bleed from the furthest point from the master cylinder first, then each side after that finishing at the front.Remember the front calis are linked and you only bleed one,which may well be where your problem is. I would maybe go down the two man route and have one on brake pedal and the other on nipples.Also I would pump out the calis until the pads are up against the discs and then push the pistons back right in on the side with no bleed nipple,whilst opening the side with the nipple so it pushes the fluid out, as,this maybe where air is trapped .I'm not trying to teach you to suck eggs,but going manual so to speak you can ensure that the nipple is closed whilst you've got the pedal at full stroke. As the auto bleed may just be letting air back in the system and with it being outside the car you can't see any air bubbles in the fluid. That's my view old fashioned maybe but it's always worked for me. Good luck

Thanks for that. Yes I'm using LHM. Sounds like the girlfriend will need to be summoned to the garage.

That could prove risky

Update: brakes fixed by a new master cylinder. Thanks to Ecas 2cv and all contributions above.