Brake help on my 81 westy!!!!

[tomtom81]

Hi All
Looking for some help......

Having some issues with my 81 2l Westy.
Have only owned the van for about 8 weeks and has been driving like a dream. I was out for the weekend last weekend for about an hour a day.
On taking the van off the drive on the Monday night all brakes have gone when engine is running. There is pressure on the pedal when the engine is off but completely goes when I start the engine.

Previous owners had masters cylinder and brake pipes changed weeks before purchasing.

I'm a little lost where to start. Have recently changed all wheels on the van but didn't think this would be anything to do with it. Just a thought.
Planning to be on a 3 week trip in her from Saturday so need to locate the issue asap really. Based in Kent

Any help would be great?????????????????
Thanks in advance

[mrhutch]

vaccum pipe split/come off therefore not recharging servo?

[tomtom81]

Thanks for the advise

I will try and have alook tonight.
Once the engine is running if I hold my foot on the break it struggles to idle and can stall. I'm guessing that links to your suggestion???

Do you think its worth bleeding the brakes?