right brake set up as follows wilwood 4 pots clamping st170 discs at front cossie 2wd discs and calipers at rear, goodridge hoses, abs removed..
the system has been bleed using a easybleed tool and seems to have a good feel at the pedal ..the problem is once i start the car the pedal goes spongy and when i press the pedal the revs rise up and down, replaced the master cylinder no sign of leakage, thinking there's a problem with the servo as when disconnected the vacumn pipe there was no vacumn in the servo although the non return seems to work, any ideas

 

The revs fluctuating suggests a leak in the system - does the system move about on the bulkhead when pressing the pedal? I have a LHD car so I dont have this problem, but I've heard of UK cars needing extra support to prevent this flex.

Worth a look anyway.

 

can u hear any air leaks in the engine bay?
is the pipe from the servo to the inlet manifold in good condition/ un damadged?

servo is a piece of cake to change any way, drain off fluid from resivoir then unbolt master cylinder.

theres four bolts at teh back of the servo take them off, get some one inside the car to press teh brake pedal this will push the linkage that connects the servo forward so u can pull the split pin out of the connecting rod then remove the little plastic pin, u may have to bend the drivers side bracket over a bit to get the pin out.

 

Keep your foot pressed on the brake pedal and turn your engine off, if the pedal rises when your foots on it the servo is knackered

 

cheers for the reply's will try all suggested and hopefully it will be fixed,going to make a new bracket up for the servo as there seems to be a bit of flex