Brake master cylinder problems!! HELP!!!

[7tradey1]

My 1996 berlingo keeps ruining the seals in the rake master cylinder. The last one only lasted 3 hours!!!!  It's the 2 pipe non abs master cylinder and its a bosch 311939. Could it be the servo ruining the seals in the master cylinder?? Also when I remove the master cylinder from the servo I get a loud hiss. Don't know if this is normal. Can anyone shed any light on this as its getting expensive now!!!

[Landmark]

Sounds to me like the cylinder bore is scored and damaging the seals
Griff

[7tradey1]

I've changed the complete master cylinder mate ( 4 times in 3 weeks!!!!) I've been told you can't buy a seal kit for this cylinder!

[ron]

I agree with Griff.Unless you are putting the seals in back to front?

[ron]

Just read your last comment after posting mine.Are you buying a reputable brand cylinder?The servo can't damage the seals as it just applies extra pressure to the piston.

[7tradey1]

Thanks guys. Yes I've bought the correct bosch 311939 master cylinder. Could it be the servo is applying too much extra pressure and blowing the seals Ron? Is it normal to get a hiss when you seperate the master cylinder from the servo? It's cost me £225 in less than a month on master cylinders so as you can imagine it's getting quite expensive now!

[ron]

Thanks guys. Yes I've bought the correct bosch 311939 master cylinder. Could it be the servo is applying too much extra pressure and blowing the seals Ron? Is it normal to get a hiss when you seperate the master cylinder from the servo? It's cost me £225 in less than a month on master cylinders so as you can imagine it's getting quite expensive now!

The servo can't damage the M/C as it exerts a longitudinal pressure.Is  the servo push rod adjustable & if so,correctly adjusted?The hissing is release of vacuum when you break the M/C /servo seal.When fitting the cylinder(s) did the brakes bleed to a good pedal pressure?Is the servo air filter clean?(usually fitted around push rod but not always.Do you have a Haynes manual? I'm nothing to do with M15,the questions are to help clarify.Good luck.

[7tradey1]

Thanks again to all that's helped with this. Yes the brakes bled to a good pressure. I've got a Haynes manual so will look to try and find the servo air filter and replace/clean as necessary before I fit my 4th master cylinder. Thanks very much again everyone. Mark

[Landmark]

When you say it's ruining the seals what exactly is happening? Are you saying the fluid is leaking back past the seals?
Are you having to apply excesive pressure on the pedal? As said the hissing is normal. To check if the servo is working correctly, with the engine OFF, press the brake pedal several times till it goes hard then, kepping the pressure on the pedal, start the engine. The pedal should then go down slightly as the servo "sucks". If not check as previously mentioned plus any servo pipes for leaks.
Griff

[7tradey1]

Hi mate. When I say it's ruining the seals I mean I'm losing my brakes altogether. The pedal just goes straight to the floor and I have no brakes at all! I summised it must be the seals but there's no external  evidence of fluid loss. Hope this makes it clearer. Thanks. Mark