Brake problem

[aferris18]

Hi everyone I have a classic mini with a brake problem

The brake pedal travels down quite far however the brakes them self still work fine I.e they will lock up and pull up straight however the strange thing is that the pedal will pump up to where it should be but not every time so roughly 5 out of 10 times it will pump up. There is no air in the system because I have bleed it multiple times using 3 different techniques but it defiantly feels like a hydraulic problem.

I have added a servo into the system for the front brakes only because the rear is too light and will lock up before the front and the rear just doesn't need to added braking force

My brake systems consists of:
A new master cylinder replace 4 months ago ( that did not make a difference )
I replaced the brake servo 2 months ago
The calipers are the standard 8.4" ones of a metro
It has a standard brake balance fitted before the servo

I have checked play in the pedal and it is well within tolerance so I am completely lost on what the problem could be so i am hoping someone may have had a similar problem they have solved or can shine some light on it for me!
Thank you for reading please help!

[Mr2Mike]

Sounds very much like you still have some air left in the system. Another, less likely, possibility is a wheel bearing problem causing pad knock-off.

[Skyedriver]

Sorry as I run i mine with 7.5" S brakes and no servo this might not help, but IIRC there is a sequence for bleeding Metro calipers, thee are two nipples????
Mine lock wheels too BTW, I have braided hoses and the pedal is at the top.

[Tempest_5]

Not the seal on the master cylinder gone is it ? I had to change one on my first classic mini with somewhat similar symptoms.

[Jefftav]

I had similar and traced it to a flexibile brake hose