GTI brakes

Need help with the brakes on my sons 89 GTI 16V, we had to replace the rotors and he bought used calipers off of ebay for the rear, the new (used ) calipers are Lucas brand and the original are Girlings, the lucas calipers fit but after we put it all together we tried to bleed the brakes and we could not build any pressure in the calipers, the parking brake works fine but the brake pedal just goes straight to the floor with hardly any pressure, do we need to bleed the front brakes too, even though we didn't touch the front brakes at all?

That is where I'd start.

So we had to replace the broken bleeder screws on the front calipers then we bled the whole system again, still the same problem, it won't build any pressure, after starting the engine still no pressure, but when I shut off the engine the brake pedal gets real stiff like it should be, start the car again and lose the pressure, even more confused now, any ideas? thanks.

If the pedal was fine when you started then you've probably still got air trapped in the system. You might want to try a pressure or vacuum bleeder system.

If when the car is off you pump the brakes and its gets stiff at the top, then hold and start the car and it goes to the floor its time for a new brake booster.

I tried that and that's what happened, I pumped up the brakes with the motor off and when I started it the pedal went to the floor, and I also pumped up the pedal with the motor running and it stiffened up then when I let go of the pedal waited a couple of seconds and pushed the pedal straight to the floor, are there any other ways to test the booster and or the master cylinder? thanks

Well look inside the car and see if there is alot of brake fluid where thepushrod goes into the firewall (that means the seals are leaking in the master cyl.)

When the car is running and you pump up the brakes alot, if the engine starts revving alot the booster is problably loosing vacuum. You can also hook up a vacuum pump to the booster and see if it holds vacuum in the diaphram. Since the car is 16 yrs old i am sure the rubber diaphram inside isnt fully intact.

well we fixed 'em!! it turns out that I needed to bleed the brakes alittle differently than I was doing, someone told me to pump the brake pedal several times and hold it down then open the bleeder screw then tighten it and repeat several times at each caliper and that's what fixed them, whhhew!! thanks for all the suggestions, maybe this will help someone else too.