RS4 / RS5 master cylinder into S4

[forty3]

This follows on from a previous thread but I'm hoping someone will see the title and be able to help me out.

After fitting RS4 brembos my brake pedal travel has increased so I've ordered an Rs4 / rs5 master cylinder and brake servo to solve the problem.

There's differing information on audizine about whether the RS brake servo is a straight swap as it usually gets it vacuum from an external pump where the S4 doesn't.

So, has anyone installed a complete master cylinder and servo into their b8 A4 / S4?

 

[Stu2w]

This follows on from a previous thread but I'm hoping someone will see the title and be able to help me out.

After fitting RS4 brembos my brake pedal travel has increased so I've ordered an Rs4 / rs5 master cylinder and brake servo to solve the problem.

There's differing information on audizine about whether the RS brake servo is a straight swap as it usually gets it vacuum from an external pump where the S4 doesn't.

So, has anyone installed a complete master cylinder and servo into their b8 A4 / S4?

I have read this all over.
When doing mine I bled the full system.
Used several ltrs of fluid to do it. Pedal is solid and travel is less!

 

[forty3]

So after getting my hands on the RS4 master cylinder and physically comparing it to one from a B8 diesel I couldn't see any difference between the two.

After some research on the manufacturers website (TRW) I discovered that the RS4 master cylinder has a different part number to the B8.5 S4 but both have a diameter of 25.4mm. This differs to the information on Audizine which showed the RS one having a diameter of 27(ish) mm.

After discovering all of the above I decided not to fit the RS cylinder and opted for the garage to carry out a complete brake fluid change to ensure the brakes were completely free of air and the result is that the brake pedal now feels much better and starts to bite right at the top of the pedal travel.

For anyone who has done the 8 pot upgrade and still has a long pedal travel I'd recommend getting a garage to do a proper bleed of the system.

Just wish I had read @Stu2w comment before ordering parts I didn't need.

Anyone need a RS4 master cylinder and brake servo with just 10k miles on it? Hahaha!

 

[Cerbera9]

I run Brembo 6pots from the S8 and after carefully bleeding them a couple of times the peddle was spot on, bite is at the top and the peddle travel and feel is better than OE. I would def echo the above comments and get the Brakes bled properly as it’s always harder with two nipples per caliper, before considering swapping the master cylinder