Yet another brake problem !!

[libbynbob]

Hi everyone,
Yet again i am trying to improve my rear brakes. Last year i bought a pattern part Lockheed 5/8" ... 15.8mm diameter master cylinder, fitted it last October but only just tonight(10th March) filled it with brake fluid and set out to bleed the system. There was no resistance what so ever from the master cylinder when the pedal was moved so i bled it using my old Easi bleed system being pressured by my foot pump. I still had no pedal resistance though so pumped up the system again and then pushed on the pedal, hey presto it worked.
Took if for a test ride and it all seemed well till my brake pedal lost all resistance again and had total rear brake failure, fortunately i was only 50 yards from home so limped it into our garage ok, thank goodness.
Any ideas and advice on whats happening here and how to fix it would be appreciated, cheers, Bob.

[Trikeman]

sounds like the seal in the mastercylinder has failed and rolled on the piston has the correct dot oil been used as this can degrade the seal extremely quickly.
Marc hiya all by the way

[libbynbob]

Originally Posted by Trikeman

sounds like the seal in the mastercylinder has failed and rolled on the piston has the correct dot oil been used as this can degrade the seal extremely quickly.
Marc hiya all by the way

Its a brand new master cylinder though Marc, can the seal deteriate while the cylinder has been stored ? The fluid is Dot 4

[Trikeman]

absolutely yes especially if it a pattern part .