Brake Issue need help A.S.A.P

Fixed my brakes , i put a petrol booster on and now they work awesome

it appears that my brakes where not fixed , so back to the drawing board

Ok, just read thru all the replies, and can offer a few thoughts.
If your pedal is still going spongey or not holding pressure when you hold the pedal down you need to isolate some of the parts in your brake system so as to rule out potential causes.
Your back brakes sound like they have had a pretty thorough checking, but for the purpose of figuring out what's causing your problem, block off your rear brake by clamping the the flexible brake hose that goes from the chassis to the diff.
Once you've clamped that line, try your pedal again. If its ok. Problem is somewhere in the back brakes, faulty wheel cyls, incorrectly adjusted or assembled brakes...
If the problem is still there, leave the rears clamped off, and repeat the process by blocking off one front calliper at a time and testing your pedal after clamping each hose, if the pedal feels better with one or both of the front callipers blocked off then you probably have bad calliper piston seals.
Hoses can also deteriorate and the internal bracing that helps the hose hold pressure can rot and break, allowing the hose to expand, but they usually blow out if they get that bad.
If after checking all that and your pedal is still shit with both front and rear brakes blocked off then check your load proportioning valve.
Everything else has pretty much been covered, I don't think its a booster or VAC issue, and your now onto your second master cyl,
Though I don't recall seeing if your still loosing fluid? If you are, and everything else checks out, start checking your hard lines for leaks.
I'm tipping front calliper seals though, I've had quite a few leaky callipers lol
Good luck, hope you get it sorted.

here is a list of every thing done to the brakes, Rear end - adjusted the drums, new wheel cylinders , replace the load proportioning valve , rear shoes looked fine so i left them , Front end - new master cylinder , booster was tested as working fine , calipers are in getting rebuilt , new pads and machined the discs , all the lines have been checked and its not leaking any where / not losing fluid , when the car is off the pedal is firm as soon as its turned on its soft , it spent 3 days in at my mechanics and even he had no idea the only 2 things i haven't changed are the vacuum pump and the vacuum line with internal one way valve running from the booster to the vacuum pump , im waiting on a vacuum gauge to test the vacuum pump but im unsure what a normal reading should be for this diesel motor , my next step is to send it in to a brake shop and let them work is out but that's going to cost big $$$$

Got the calipers rebuilt , new pads and machined discs refitted and re bleed the system , still have the same problem , im outta ideas now other then the vac pump ?

Your in Australia yeah Aaron? Where abouts? I'm in Sydney.
Have you started the engine with the vac hose pulled from the booster? If yes, I'm guessing the pedal doesn't change?
The reason your brake warning light is coming on when you pump the pedal at idle is Cause you've used up the available vacuum that had built up in the booster, a safety feature so you don't go to apply the brakes normally only to find out you have no vacuum assist.
It not uncommon for diesels to have a softer pedal than their petrol counterparts due to the VAC pump in most cases creating vacuum all the time as opposed to a petrol engine where intake manifold vacuum can vary greatly depending on rpm and throttle position.
If your pedal is hard until you start the engine and drops a bit once started, then that's pretty normal, after all, its VAC assisted braking and is allowing you to exert more force into your braking system.
If your not loosing fluid, if the brakes operate consistently under normal conditions and your not suffering from brake fade then it may just be a case of getting used to a different vehicle.

im on the gold coast , i pulled the vac hose from the booster with the truck running the the pedal went rock hard , the pedal drops all the way to the floor once the truck is started and its unsafe to drive like that as it locks up the rear brakes every time , some times you can push then pedal really softly and they work fine other time it just drops to the floor , its like there is no resistance at all at the brake pedal once the vac pump starts running , i got it booked in for the 23/7 for a brake shop to go right over the whole breaking system hopefully they can sort it out because im out of ideas

brakes are now all fixed and working sweet turns out there was no reaction disc in the booster . had one fitted and fixed all my problems