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no pressure in the brake pedal

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no pressure in the brake pedal

hi, i will go through the list of parts 1st.
brand new rear brake drums, and everything inside the drum is new
brand new handbrake cables
brand new copper piping throughout
brand new 22mm master cylinder
brand new fluid
2nd hand rust free 9" servo
4x goodridge braided hoses
280mm front calipers + new adapter brackets
all the seels r in tact and there r no leaks anywhere

c the prob is there is no pressure in the pedal when the engine is on, when the engine is off there is a good buildup of pressure when u pump the pedal but when u turn the engine on whilst pushing hard on the pedal it is supposed to move about another inch tops when the servo kicks in but its just sinks (not to the floor) but as far as the pedal can go. from the pedal sitting itself to being pushed down it should gradually get tougher to push until u cant push any further but it doesn`t it feels like im pushing on the gas pedal there is no resistance.
 the odd thing is when u push it down u can see the front calipers biting into the disk so there is plenty of movement, the fluid is moving well and the backs r locking up to.
i have blead each pipe starting with the longest 2 shortest with the easybleed system pushing through a full tub of fluid in each pipe, all in all with doing it myself and having help i have prob tried to bleed the brakes easily 12-15 times.
 i have changed the master cylinder from 1 that i got with the servo to a brand new 1 thinking the fluid is passing the middle seal and im still getting the same effect (thats £75 i`ll miss).
 i have changed 90% of the vacuum hoses  

i keep on cumming up with the same thing, its something to do with the vacuum, but what?? when the engine is off there is a good pedal, when u turn the engine on the servo assists the braking and lets the pedal go down a little bit more but on mine it lets the pedal go down a few inches, its as if the servo is doing its job to well i.e. if the servo on brakes that work helps the braking by 10% it feels like its helping mine 90% and taking the build up pressure the pedal is supposed to have away, as i say its like its doing its job far to well……..

any ideas please?????  i am running of ideas and getting really fed up with the whole thing, i just want them to work………

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As you seem to have changed everything i wonder it its the linkage needing adjusting, this does need setting correctly when fitting 16v servo/master cyl. As you summise i think starting the engine is then giving you some servo assistance which then makes the pedal sink further.

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i read the thread on this site about installing a 9" servo an 22mm master and the only thing it says (that i can remember) about adjustment is cutting 10mm off the bolt thread which goes onto the clevis pin onto the rod.

the pedal has a small amount of movement/play (less than 1cm) when it sits itself. if i adjust the rod length what will it do and what way should it be adjusted, i dont want any more play in the pedal as it leaves the brake lights on.
there is an adjuster down at the pedal as well but i cant think what good it will do the prob at hand by messing about with that

this is me right now :banghead:

suggestions??????????????

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i came up with another thing to try just on the off chance, if the pedal is gd when the engine is off and the pressure in the pedal is lost when the engine is on im going to try bleeding the brakes when the engine is on, sounds crazy but if the servo is on when i bleed the corners it might hold the pressure better, f~_k nose, need help people………….

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Try it but i dont think bleeding with the engine running will help, i think you need to try and narrow it down, for instance disconnect and plug the rear brakes,bleed, try the pedal then the fronts and see if either makes a difference.

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i have noticed that there is a diafram bolted onto the airbox with a thin plastic vacuum pipe going into 1 of the 2 molded inlets onto a rubber hose that connects into the inlet manifold and also the servo pipe, when i looked at the hynes pic of a engine it showed a vacuum accelerator in between the bulk head and pass suspension strut, it had a pipe going to where my pipe goes, is that what i have, r they the same thing? when i checked the connectivity with a multi meter between the 2 pins on it there was no connection and i checked other 2 pin att around the engine and there was a connection, is this my prob? what does this diafram do? could it be the reason i have no build up of pressure in the pedal when the engine is running???

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dont worry about those, nothing brake related. if you suspect they are a problem disconnect them entirely and cap off the nipples on the brake servo pipe to rule them out. all you are interested in now is making sure the servo has good vacuum.

does pumping the pedal help? if so theres air in there. if not maybe the servo is the problem or its not getting vacuum. ion my cabby i managed to fit the non-return valve on the servo pipe the wrong way round, so check that!

are the front calipers the right way up? make sure the bleed nipples are at the top. look over everythign carefully make sure no fluid is seeping past the piston seals or rear cylinders

Hello my name is John and I'm a dub addict.



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Sorry to drag up an old thread but what was the outcome of this? I have the exact same issue, and I'm struggling to sort it.
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