Do I need to upgrade the brake mastercylinder when going to 345mm brake setup..

[soulwaffle]

Hi All,

I uprated the brakes on my audi a3 2.0l tdi to the 345mm brakes. Ever since the upgrade I notice that when I press and hold the brake pedal it slowly creeps to the floor. I have followed the audi way of bleeding the brakes + vagcom etc. I've got the car in bits right now so was thinking of swapping out the brake master cylinder.

So my questions are do I need the S3 brake master cylinder? And if so, will I need to swap the brake servo (hopefully not) or shall I just buy the same brake master cylinder?
Part numbers:
1K2 614 019 J = ATE - S3 [345mm]
1K1 614 019 H = ATE - CFFB [2.0l tdi]

 

[NHN]

Nope, don't need, you need to grab a gunson bleed kit, its got air in the system, done this numerous times & I've fitted RS3 brakes using the same MC etc with zero issues, once bled properly.

 

[soulwaffle]

Nope, don't need, you need to grab a gunson bleed kit, its got air in the system, done this numerous times & I've fitted RS3 brakes using the same MC etc with zero issues, once bled properly.

I used the Sealey bleed kit, pic:

 

[TDIb0y]

I did the S3 front brake conversion on my own A3 2.0 TDi without changing the master cylinder... No issues at all, so I'd agree with NHN that it's not needed.

However, if you can't get a firm pedal then it could just be coincidence that you may now need to look at the MC!

Also, I've always trusted the 'two-person' brake bleeding method... if someone in the car is standing on the pedal and you're the one turning the spanner at the caliper and seeing the air bubbles come out, it helps you know what's really going on and if the bubbles ever actually stop (suggesting an air leak somewhere in the system).

 

[soulwaffle]

I did the S3 front brake conversion on my own A3 2.0 TDi without changing the master cylinder... No issues at all, so I'd agree with NHN that it's not needed.

However, if you can't get a firm pedal then it could just be coincidence that you may now need to look at the MC!

Also, I've always trusted the 'two-person' brake bleeding method... if someone in the car is standing on the pedal and you're the one turning the spanner at the caliper and seeing the air bubbles come out, it helps you know what's really going on and if the bubbles ever actually stop (suggesting an air leak somewhere in the system).

Hmm, I always thought you stop bleeding once the air bubbles stop? I mean, I can still see small tiny ones but the large ones eventually stop coming out...When I changed the calipers, I swapped out the hoses and put in braided lines.

I've ordered a MC, £20. No harm in swapping it out.

 

[TDIb0y]

Yes exactly - if you were always drawing out bubbles then the system must not be properly sealed. I find it reassuring seeing the situation at the caliper myself, whilst also acting as the 'valve' by opening or closing the bleed screw directly.

Will be interested to know if replacing the master cylinder solves your problem - might have just been bad timing.

 

[kuebk]

After swapping front to 345 no issues at all, after I swapped rear to 310 had some issues which were solved with coding ABS for bigger brakes.
No need to replace master cylinder.