Brake info required!

[Budgie]

Got a wee problem with the brakes on the Disco.  :(

Normal driving is OK but if I have to stand on the brakes then they seem fine to start with but then the peddle slowly heads towards the floor and no matter how hard I press or pump the peddle there is no more braking available!!  :shock:

With the engine off there is plenty of pressure on the peddle and it doesn't move, the servo is working as that's been changed and tested. I've fitted a new vacuum pump and the pipe from the pump to the servo is in good condition with no leaks and all the connections are good. The one-way valve on the servo is working and there are no leaks in the system. I've bled the system and there was no air in it.

All the problems started when I fitted a new set of pads to the front and it's a solid disc, non-ABS system.  

I've run out of ideas, anyone got any? [-o<

[beast5680]

are the pads contacting the disc flat? i had an old car i changed pads on and the discs were fairly worn so the new pads were only touching the discs on the outer edge of the pads , the edge was doing all the braking which was fine to start with but it meant the pedal was funny as the more you pushed it down it distorted the pad against the disc

[Budgie]

The pads are OK on the discs & the front discs are two year old EBC slotted & drilled ones.

The calipers have only been on about a year, although it may be worth checking the cylinders again to make sure they are free as the salt air plays havock with everything up here!  :?

[imspanners]

It's normal.
The vacuum pump on a diesel will draw the master cylinder down because it's a consistant pull all the time.
Whereas a petrol only has a limited vacuum drawn from the inlet manifold.  

Just be worried if the pedal sinks under pressure without the engine running.  

[blackbob]

sounds like a master cyl prob
is there any fluid loss if not
if you take the master cyl out and pull the seals see if there split or if the bore is scratched

[Budgie]

That was my plan for the Sunday Bob, I've got a spare master cylinder so I'm going to swap them over and re-bleed the system again to see if that make any difference, after checking the front calipers.