Okay, here is the problem.

I own a sei 1108, and i experience an extreme softness in the pedal while braking.
worst then it has ever been (it wasn't that good in the first place).

As long as the engine is turned off, the pedal is rockhard, but as soon the engine is running, it becomes very soft, and to brake propperly you have to push it all the way down. When doing this, the car brakes fine, but only when your foot is almost touching the floor.

The car is an issue featuring ABS, the Master-Brake cylinder has just been changed, and only made a small difference in braking power, even though the ABS system has been "updated" as the lads at my local garage claimed. consequently, the braking fluid has been refreshed.

Can anybody tell me anything about this problem, or have some experienced the same problem?

Sounds likew the brakes not bled properly. I'd have said master cylinder, but.........

Have had a similar problem on a mini. Try bleeding the master cylender first, slacken the unions off and pump a little brake fluid out as you would with a wheel cylender.

Check the compensator unit, or whatever you call it nowadays. This is next to the master cyl on the bulkhead. strip and clean, bleed as the master cylender.

Some cars I have worked on have been a real problem to bleed brakes. one thing I have done is to lock each flexi pipe with a brake hose clamp, and bleed each wheel seperatly, this prevents fluid moving back and forth in the parts your not bleeding.

Other than that it is the usuall check everything.

Thanks for the info!
I'm going to work on it.

On a Seicento with ABS, there are no compensators as they are part of the ABS pump module. Have you replaced any discs/drums/shoes etc?