Master Cylinder or Servo??

[fleming]

Have just serviced my brakes on the valver, new discs, pads, drums shoes, wheel cyliners, flexi hoses and brake lines. When the engine is switched off there is a good pedal, when you start the engine up - for the first 6 pumps there's a good pedal. Then after this when you pump the pedal (as you press the pedal you start hearing the servo hiss) the pedal has a lot of travel before it does anything. Is this a master cylinder problem or a brake servo problem??

Im lost on this so am after some assistance.

Thanks people

[m.d.]

sounds like the pipe to the brake servo has split or the servo has perrished inside. deffo not the master cylinder as they normally cause no brakes at all

[5toprjepog]

m.d is totally right first thing to do is
Pump the pedal a couple of times with engine off then push as firm as you can on the brake pedal start the engine keeping your foot on it, it should drop a little, if so thats alright still keep your foot on it for 20 second if it creeps to the floor your servo has gone you cant repair it your self so get a new one.

[Aragorn]

why would a faulty servo cause it to creep to the floor?

servo just amplifies the mechanical input from your leg

if it creeps to the floor its the master cylinder

[General Baxter]

lol,

just replace both :lol:

[5toprjepog]

Cause the servo builds up presure from engine when you start engine it adjusts due to this thus making it drop if the pressure is not keeping up then there will be now fell to the breaks and it will be leaking air if it was master cylinder it would leak with engine turned off

[Aragorn]

all the servo does is amplify your push

if the pedal sinks to the floor once engine is on you would find that if u pressed VERY hard on the pedal with the engine off it would sink too

once the hydraulic circuit is upto pressure (ie your foot is jammed on the brakes) the only way the pedal can go down more is if the hydraulic circuit loses pressure and the only thing attached to the hydraulic circuit is the master cylinder NOT the servo

so its either leaking MC seals or a leak somewhere else

you've prolly buggered the seals in the MC by pumping the pedal repetatively when u were trying to bleed the brakes, u should invest in a pressure bleeder and use that instead - much better

[fleming]

We've got a suction system which draws the fluid through the system so we didnt damage it when we blead it. Then we did a final manual pressure bleed. But people ive spoken to have said that its more than likely the master cylinder.

Keep some ideas coming though people - have got to cure this problem. Its driving me mad!