Brake pedal rise and fall ?

Hi All ! a couple of days ago i noticed that the brake pedal rises and falls when i press the accelerator ? is this right or do i have a leak somewhere in the system or a possible blockage . Another thing i noticed was air being drawn in through the petrol filler cap when engine is running ? cant remember it doing that before now either ? any ideas would be a great help , cheers in advance

 

It's possible your brake pedal return spring has snapped allowing the weight of the pedal to press slightly on the servo, actuating it and adding more braking hence the pedal going down further. Faster engine = more vacuum.

To test a servo, you pump the brakes, keep the pressure on the pedal and start the engine. As the engine starts the pedal drops 1/2"-1" showing the servo is working. It sounds like yours is doing something similar on it's own. If it's not pulling as well as it usually does and the brakes are getting hot...

 

Cheers Zed i'll try that test mate

 

I wasn't suggesting you try the test, rather I was explaining how I'd come to the conclusion your spring may be snapped. Pull the brake pedal - there shouldn't be any free play pulling up. If it's sunk down (engine off) look at the spring underneath.

 

It looks like this flying pig

 

...only covered in Marmite.

 

Ok Zed ! now i get ya i'll check out the spring later today . Cheers paradox i know what to look for under all the **** now LOL