Occasional soft brake pedal

[detch]

So my brakes are fine.
My car stops fine.

But sometimes, suddenly my brake pedal feels very soft and my foot has to travel deeper to make the car stop. It feels horrible.
However if you "pump" the brake, it's fine again.

I flushed the brake fluid thinking it may be water in the system - but no.
Obviously the fluid is topped up.

While pushing the brake when stationary it makes a weird "squirting sound" - like you're trying to suck the last two sips using a straw.
Any ideas what to investigate next?

 

[PDJ]

to suck the last two sips using a straw.

Don't drink the brake fluid....

Completely drain the brake fluid and re fill then bleed the system starting at the calliper furthest from the master cylinder longest pipe run so rear right then rear left followed by the front left then front right


Use an easy bleed system to help empty the system and be prepared to use around 3 ltrs of fluid (it keeps if you don't open it)

You can tap or thump the calliper with a rubber mallet to help free the last bit of air

You may also have a vacuum leak to the servo this could give you the sucking sound