I would like to increase the size of my front brakes.
Currently, the front axle is equipped with 280mm brake discs and the FSIII caliper.
It would be interesting to upgrade to the larger brake system that is also used in the S3, TT (I believe the Golf V6), etc. It's the large saddle and the 312mm disc.
The saddle mount is a different design, that's clear. But is it enough to just take the S3 axle bracket, or do I need other parts as well?
You need the wheel bearing housing, new seat stays, new brake calipers, rotors, and pads.
Just the calipers cost €118 each (!), plus the brake discs (each €119), rotors (each €127), pads (€121), and heat shields (€5).
The wheel bearing housing costs about 150,-, but if you don't have a Quattro model, you should get one from a 1.8T with front-wheel drive, not one from the S3.
Yes, it looks like it would fit (except for the cover plate).
I'm not familiar with the differences between the Quattro and non-Quattro front axle components (even though there are differences, at least in the part numbers).