[j111mcr]

Any suggestions will be welcomed .

With the engine switched off my brake pedal is good and solid , as it should be .
When the engine is switched on and you depress the brake pedal it gradually creeps down .
The brakes are good on a normal run and I am not loosing fluid .
I had the brake fluid changed completely and all corners were bleed to see if I could get a solid pedal with the engine , but it is still the same .

 

[Speedy]

Surely that's the way it should be? Once the engine is running you have servo assistance. Try stopping a car going downhill with the engine off - especcially a big car and it's bloomin' difficult! If the brakes are functioning properly and I assume the pedal doesn't sink to the floor when you have to stop? That would be a problem!

 

[bigiainw]

It's a natural part of the servo building vacuum.
Iain

 

[Big Al]

Had the same problem. the pedal should drop down when the engine is running because the pedal pressure is increased because of the servo assist, but it should not keep going to the floor and if you release and press again and it still goes down to the floor you have a problem in the master cylinder. usually it is thethe main piston seal which is passing with the extra pressure from the servo, instead of pressurising the fluid to the brake cylinders and holding it, some fluid leaks back past the seal back into the header tank. to be on the safe side I changed mine you can not get just the rubber seals have to buy a new unit from main dealers over £100 , easy tochange but see if you can pre- bleed the unit before fitting it [look on tinternet changingandpre bleeding master cylinders]and when you bleed the corners start furthest away from master cylinderand have the ignition switched on to activate the ABS system and open the ports.

 

[j111mcr]

thanks to all who replied . I tried a friends 2008 today and it did exactly the same . With the engine running and you press the brake pedal it sinks slowly .release and try it again it still sinks slowly .

Normal Braking on mine is good at the moment but I'll remember the advice on the master cylinder .
thanks again ....