The Forgotten On

My car is a 1981 US 928 and I am going to swap over some 993 brakes (same as S4)
and would like to know if I should change out the brake master cylinder to a later
S4 one that I have on a booster I will install soon.
Or is the original master big enough to supply enough fluid to the calipers without putting the pedal to the floor.
I just want to know and I am sure others do too as this particular topic on master cylinders has not
been widely talked about from what I have seen.
All input would be greatly appreciated.

Mrmerlin

FWIW the early MC is quite different from the later S4 due to the early unit having to supply the brake pressure regulators under the MC, as well as the brake pressure switches being part of the early MC
the S4 MC feeds to the ABS unit and has no pressure switches

The Forgotten On

Thank you Mrmerlin. I would also like to know if I should get the 55 bar bias valves to make the rears work a little harder.

Mrmerlin

is this 55 bias valve your referring to for the ABS cars?

The Forgotten On

No, the ones that mount to the body on a 964 turbo. This isn't the brass tube looking one that sticks out of the brake master.
These can swap between all of the cars as I know that many S4 owners are putting the 33 bar ones from the early cars in theirs as a cheap brake boost.

Mrmerlin

I am not familiar with this part

The Forgotten On

It is the two things on the bottom underneath the master cylinder. All of the cars have at least 1, the early cars have 2.
The later cars have a small cylinder one that goes into the ABS system along with the one that mounts to the body of the car.