Terrano brake issues

[grytvikken]

Hi I have an old 89 2,7 d21 turbo diesel terrano that has an issue with the front brakes.; I recently replaced the front pads and after pushing back the pistons and fitting new pads I cant get the pedal pressure back. I have bleed the brakes both front and rear and even though the rears are bubble free the front drivers side is refusing to clear up. Now after spending ages trying to get the brakes bleed I replaced the front 2 calipers with a couple of spares I had. ......same issue. I can pump up the pedal get pressure and if I hold the pedal on after pumping it stays hard.....release the pressure and push again it goes all the way to the floor.
Started to suspect the master cylinder....so i removed brake lines and fitted 2 bolts and copper washers and the master cylinder pressure stayed hard......assumed cylinder ok. went back to calipers and checked for any fluid leaks ...there are none visible. Attempted to bleed again ...all bubble free both rear and passenger side. Drivers side small bubbles....tried bleeding them out till leg feel off. Then decided to clamp off rear rubber brake hose at diff and the hoses at front brake calipers....pedal high and hard , unclamp rear hose, no change pedal hard......unclamp pass side clamp pedal drops to floor. Reclamp pass side then unclamp drivers side pedal goes to the floor. Am wondering what to do next , All was well until I changed the brake pads .......most confused.
Friend suggested that the master cylinder could still be issue even though it stays hard during previous tests. Any opinions? Could just buy new cylinder and try but money is tight and at $150 or there abouts I would rather know before wasting money that I dont need to waste. Thought about swapping out with d21 navara one at wreckers but am unsure if they are compatible....read one post once about master cylinders being different if the donor car has rear drums.
Have bleed a lot of brakes in my time and this has me stumped.
Any advice would be happily recieved

[Colinl]

To me I'd say suspect master cylinder, could be pulling in air on the return stroke.
I'm no mechanic by any stretch though..

[grytvikken]

just swapped over master cylinder from another car and still same symptoms......damn should have put mine on his car to see if it caused same issue with his, shit shit shit, didnt want to hold up other bloke too long

[Crash bandicoot]

excuse my typing on on a msart phone and have mechanics hands.

1...get some one to press the pedal whilst you cisually inspect the caliper end of the brake lines, if it has been 50-60-100 thousand ks since the pads were last done the lines could have gone brittle then when removing hte calipers to change the brake pads the inner lining has cracked allowing to flow up the reienforment inside the walls of the brake hoses.

2...(and probably most likley) twin pot calipers yes? cut a piece of wood the same thickness as the new pads and rotor, unbolt the caliper and stick the block of wood in and watch the pistons work,, if all appears well move the calipers around upside down etc then return them to a postion where the bleed screw is at absolute vertical, get some one to stand on the brake and then crack the bleed screw.

but in saying that, if they were fine before the pad change then it is the bleed proccess at fault, will still be air there somewhere, have you tried bleeding hte other way, forcing hte fluid back up the line from the caliper end ?

[grytvikken]

Will try all points made....fitting my master to mates car tonight all good so master cylinder not the issue. thanks for input guys