Master Cylinder Upgrade for Big Brake Kits Thread

[PeteRock]

Hello! As there seems to be some differences between cars I wanted to see if anyone here has done the RS5 Master Cylinder/B8 Booster conversion on a B8.5 S5? If so can you confirm that these specific parts below are correct and will fit?

Thanks!

RS5 Master Cylinder (8T0611021)

B8 S5 Booster (8K0612107B)



Pete

[PeteRock]

Hello! As there seems to be some differences between cars I wanted to see if anyone here has done the RS5 Master Cylinder/B8 Booster conversion on a B8.5 S5? If so can you confirm that these specific parts below are correct and will fit?

Thanks!

RS5 Master Cylinder (8T0611021)

B8 S5 Booster (8K0612107B)



Pete

Anyone do this upgrade on a B8.5 S5 that can confirm these part #s?


Pete

[avantagg]

Anyone do this upgrade on a B8.5 S5 that can confirm these part #s?


Pete

I have a brand new RS5 MC that never made it into my car. I can post a few pics when i get a chance, considering selling it.

[PeteRock]

I have a brand new RS5 MC that never made it into my car. I can post a few pics when i get a chance, considering selling it.

Ok great! Same part # that I posted? I might be interested as I haven’t picked one up yet....I get a nice deal on Audi parts though so it probably need to be a pretty good price...let me know! Thanks!


Pete

[avantagg]

Ok great! Same part # that I posted? I might be interested as I haven’t picked one up yet....I get a nice deal on Audi parts though so it probably need to be a pretty good price...let me know! Thanks!


Pete

Never ended up installing it. Shoot me a PM if interested.

[red4life5]

I have “stock”B8 A4 brakes except for stainless steel lines. Would upgrading the the RS5 master do anything for me?


2010 A4 S-Line Prestige

[IllusionalTA]

fwiw, I've got the rs5 calipers and crap, and stock b8.5 master, and it stop's fine.. pedal feel is fine..

[LittleDevil]

If anyone interested I found 2 x NEW RS5 Brake Servo (8T0612107) and 2 x NEW RS5 brake master cylinder (8T0611021) in garage when cleaning it... If you upgrade BBK to S4/S5 it is recommended to change it... Those parts are Originally installed in RS5 B8 and B8.5 with Ceramic Brakes.

[PeteRock]

If anyone interested I found 2 x NEW RS5 Brake Servo (8T0612107) and 2 x NEW RS5 brake master cylinder (8T0611021) in garage when cleaning it... If you upgrade BBK to S4/S5 it is recommended to change it... Those parts are Originally installed in RS5 B8 and B8.5 with Ceramic Brakes.

Do you still have the master cylinder? Is it brand new? How much are you asking?


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[LittleDevil]

Do you still have the master cylinder? Is it brand new? How much are you asking?


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Still have both items. PM replied.

[PeteRock]

Just to confirm if I have a B8.5 S5 and want to use the RS5 Master Cylinder then I would need a B8 S5 Booster correct?

I don’t think that you can use the RS5 Master and Booster combo on a B8.5 but I’m not 100% sure

Can someone confirm this?


Pete

[smudgeface]

Did anyone ever confirm how to do the ABS reset with VCDS? I didn't see it...

Can someone enlighten the rest of us?

[oldzmann]

Did anyone ever confirm how to do the ABS reset with VCDS? I didn't see it...

Can someone enlighten the rest of us?

+1

[niner]

Got a question for guys that have done the swap: is there enough room to pull the master cylinder and brake booster, without removing the "fake" firewall? It looks very tight behind the MC, but I haven't attempted yet.

Thanks!

[niner]

Got a question for guys that have done the swap: is there enough room to pull the master cylinder and brake booster, without removing the "fake" firewall? It looks very tight behind the MC, but I haven't attempted yet.

Thanks!

Dig around a little more. It seems like I should remove and reinstall both the MC & booster together as a complete unit.

[smudgeface]

Thought I’d chime in here, for future readers. I did the full RS5 caliper swap on my B8.5 S4 and also replaced front and rear brake lines with stainless. I bled the system twice with a motive pressure bleeder. Initially, I felt pedal feel was not great but, I’ve been driving it this way for months now and it’s a lot better. I’m not sure if maybe any last bubbles in the lines have worked their way out or maybe I’m just used to the feel. But, I no longer feel the MC and piston swap is even necessary...
Anyways, just my $0.02.

[makisupa]

Ok so I'll add my 0.02 too...

I upgraded to the RS5 MC and RS5 booster on the recommendation of my shop who had the RS5 upgrade on his B8.5 S4. I will add that I am running the RS7 OEM kit (390 wave rotors) up front and the Voshmods BBK (dual caliper set up) on OEM RS7 (356 wave) rotors in the rear. A fellow allroad owner is running the full Voshmods front (390) and rear BBK kits dual caliper on a 356) and complains of entirely too much throw and poor feel. I use this as a comparison to my set up.

I feel like my investment was worth it in the end due to his similar set up and complaints about his set up. He intends to upgrade them both like myself, it is his only complaint about his BBK

DSC_0023_2.jpgimage1-1.jpeg

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[voshmag]

Ok so I'll add my 0.02 too...

I upgraded to the RS5 MC and RS5 booster on the recommendation of my shop who had the RS5 upgrade on his B8.5 S4. I will add that I am running the RS7 OEM kit (390 wave rotors) up front and the Voshmods BBK (dual caliper set up) on OEM RS7 (356 wave) rotors in the rear. A fellow allroad owner is running the full Voshmods front (390) and rear BBK kits dual caliper on a 356) and complains of entirely too much throw and poor feel. I use this as a comparison to my set up.

I feel like my investment was worth it in the end due to his similar set up and complaints about his set up. He intends to upgrade them both like myself, it is his only complaint about his BBK

DSC_0023_2.jpgimage1-1.jpeg

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As nice as possible.... If only a couple have pedal issues and at least 50 kits on road with spectacular pedal feel, I would look at bleeding and pad selection again. I bleed it like I'm doing a brake flush, I will waste fluid before I waste my time.

Please have your fellow allroad friend reach out to me so we can resolve his/her pedal issues.

Its not my my kit I can assure you. Its not possible as it is well within spec of the oem master cylinder.

These are ballpark numbers and in comparison to the OEM caliper: 1.8% decrease in needed volume for my rear kit 2.4% increase for front kit.

Things to investigate:
Bleeding...
Bleeding...
Bleeding
Pad selection (no such thing as a low dust high performance pad)
Are you glazing rotor
Is your master cylider healthy

If this list checks out.... Go back to bleeding


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[blackfunk]

As nice as possible.... If only a couple have pedal issues and at least 50 kits on road with spectacular pedal feel, I would look at bleeding and pad selection again. I bleed it like I'm doing a brake flush, I will waste fluid before I waste my time.

Please have your fellow allroad friend reach out to me so we can resolve his/her pedal issues.

Its not my my kit I can assure you. Its not possible as it is well within spec of the oem master cylinder.

These are ballpark numbers and in comparison to the OEM caliper: 1.8% decrease in needed volume for my rear kit 2.4% increase for front kit.

Things to investigate:
Bleeding...
Bleeding...
Bleeding
Pad selection (no such thing as a low dust high performance pad)
Are you glazing rotor
Is your master cylider healthy

If this list checks out.... Go back to bleeding


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See post #12. People believe what they want to believe, facts be damn. I'll say it again, the pistons are sized in a way that the overall volume of fluid required to fully extend the pistons fall within the margin of error for the stock pump which I wouldn't be surprised if it has its own margin of error of at least 20%. Ergo, it can easily absorb just about any reasonable piston change that's thrown its way.

[voshmag]

See post #12. People believe what they want to believe, facts be damn. I'll say it again, the pistons are sized in a way that the overall volume of fluid required to fully extend the pistons fall within the margin of error for the stock pump which I wouldn't be surprised if it has its own margin of error of at least 20%. Ergo, it can easily absorb just about any reasonable piston change that's thrown its way.

100% facts. Much like tons of people swearing 19z calipers due to their massive psitons will need a m/c upgrade.

On a B7 a4 avant I have installed my piston Brembo rear bbk and brembo 19z (from Cayanne Power package) upfront. Used quality pads, quality rotors, braided lines and bled it properly. Rock hard pedal.

Buy I use the cowboy method when bleeding. Literally I use 2x the fluid I actually need and flush the whole system

Presssuer bleeder on reservoir and do in this order

PR, DR, PF,DF

On each side I do bleeders like this

1st rotation
Inside long bleed, outside long bleed, inside long, outside long... Then move to next corner

2nd rotation
Repeat long bleeds


3rd rotations
Power bleeder on reservoir (mainly so I dont have to watch fluid level and take in air)
Friend does 5 pumps the short cracks of inside bleeder. Do this three times them move to outside bleeder and do 5 pumps pedal cracking bleeder quickly 3 times


Repear 3rd rotation twice. This time I tell friend to say "floor" before they hit floor but i only use that as indication something is wrong. I litterally juat burp the bleeder and close. 5 pumps... Burp... Close... 5 pumps... Burp... Close.


May not be the correct way, but has always worked... Always.


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[voshmag]

100% facts. Much like tons of people swearing 19z calipers due to their massive psitons will need a m/c upgrade.

On a B7 a4 avant I have installed my piston Brembo rear bbk and brembo 19z (from Cayanne Power package) upfront. Used quality pads, quality rotors, braided lines and bled it properly. Rock hard pedal.

Buy I use the cowboy method when bleeding. Literally I use 2x the fluid I actually need and flush the whole system

Presssuer bleeder on reservoir and do in this order

PR, DR, PF,DF

On each side I do bleeders like this

1st rotation
Inside long bleed, outside long bleed, inside long, outside long... Then move to next corner

2nd rotation
Repeat long bleeds


3rd rotations
Power bleeder on reservoir (mainly so I dont have to watch fluid level and take in air)
Friend does 5 pumps the short cracks of inside bleeder. Do this three times them move to outside bleeder and do 5 pumps pedal cracking bleeder quickly 3 times


Repear 3rd rotation twice. This time I tell friend to say "floor" before they hit floor but i only use that as indication something is wrong. I litterally juat burp the bleeder and close. 5 pumps... Burp... Close... 5 pumps... Burp... Close.


May not be the correct way, but has always worked... Always.


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Also... Just my 2 cents. I like hawk pads but not for this application. 5 counts of soft pedal resolved by ditching hawk and installing EBC reds then doing proper break in.

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[smudgeface]

Yeah, that totally makes sense. The added fluid volume requirement of the extra set of rear calipers pretty much makes the master cylinder upgrade mandatory. I still have the standard single electronic rear brake.

[voshmag]

Yeah, that totally makes sense. The added fluid volume requirement of the extra set of rear calipers pretty much makes the master cylinder upgrade mandatory. I still have the standard single electronic rear brake.

Statements like this make forums so confusing. What is good info and What is a logical (but incorrect) guess.

Rear Brembo has more piston (4) but they are much smaller than the single piston oem caliper. Then Look at the difference between the floating OEM single GIAINT piston that must pish+pull on every pedal movement vs A fixed caliper with smaller pistons that only need to push to apply pressure.

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[tom101]

Hi, I want to thank you the research you did for the upgrade, its awesome.

I own A5 2007 with turbo upgrade and brembo, and I want to do this upgrade.

But TRW PML358 is out of sale in europe 1 year ago. And buy from Audi dealer is very expensive, over 400€.



Anybody knows other master cylinder upgrade options? A6, Q5, Macan?

thanks

[iAwesomE]

RS5 Booster and master combination works. Unfortunately I learned it the hard way. We put it in, I started the car and pedal felt like a rock, no boosting at all. I panicked and had the B8 booster overnighted. We put that one in and it was the same thing! No boosting. So, it turned out the ABS had to be reset with an OBD2. Should I have known that I would have had a nice silver RS booster VS black B8 one.

I have the RS5 Booster for sale by the way....$250 shipped.

I am planning to do this mod, and was wondering if anyone know the VCDS adaptations to reset the ABS that FlyS4 did here? Thanks in advance

[lunarPower]

Sorry to dig up an old thread. But I was doing some research in ETKA... looks like the part number for the s8 armoured edition piston (28.57mm) is "4h6-611-021" or TRW PMN229. It is extremely expensive at 1 to 2 thousand US dollars.

There is also probably a compatible TRW 27mm / 26.99mm MC but I am not exactly sure which part # would work. I found this site that is selling a 26.99mm in the UK for $147. No idea what TRW part number it actually is https://www.ultraperformance.co.uk/t...aster-cylinder.

[3.0ss]

Does anyone have removal instructions for the MC they could share? I can't find anything online, I'm wondering how involved the removal is.

[lunarPower]

Does anyone have removal instructions for the MC they could share? I can't find anything online, I'm wondering how involved the removal is.

Does this help?

1.jpg2.png3.jpgdiagram.pngpedal_seperate.png
mc_1.pngmc_2.png

[3.0ss]

Does this help?

1.jpg2.png3.jpgdiagram.pngpedal_seperate.png
mc_1.pngmc_2.png

Yes thank you!


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[rubicant5x]

This thread brings me back. Glad it was able to help so many. Cheers!

[lunarPower]

Again sorry for digging up an old thread but I am late to the game in upgrading my B8.5 S4 with RS5 8-pot brakes. I just got my hands on both a 2014 RS5 and 2011 B8 S4 master cylinders + brake boosters. There is a lot of differing information in this thread so I thought it was best to completely disassemble both sets of components, compare the internals and share my findings.

Part numbers used:

2011 S4 Brake Booster (TRW B8 - 8K0-612-103K) (confirmed in ETKA as a legacy B8 S4 booster part number)
2014 RS5 Brake Booster (TRW RS5 - 8T0-612-103A)

2011 S4 Master Cylinder (TRW 6458 9513)
2014 RS5 Master Cylinder (TRW 6458 0764)

Major take away:

Master Cylinder:

-The master cylinders between the RS5 and the S4 externally look almost identical. However internally the RS5 has a bigger piston and bore (circa 25.5mm vs 27mm).
-The top, externally visible parts of the piston have the same stroke and diameter.
-The RS5 master cylinder has 2 holes for reservoir feed channel and the S4 has 1 hole. I am not sure if this is a design revision to over come a flaw, or if it has functionality in allowing larger fluid volume.
-Functionally the RS5 master cylinder should create more fluid pressure with the same stroke which makes sense to support actuation of a larger caliper piston area.

Brake Boosters:

-The brake boosters are externally dimensionally exactly the same.
-The RS5 brake booster is made of Aluminium while the S4 brake booster is made out of a ferrous metal.
-Due to the metallic composition of the RS5 brake booster, it is much lighter than the S4 one.
-The output and input shafts, pistons, springs, and boots are exactly the same.
-Internally the S4 brake booster has a differing part number for the secondary, output side diaphragm.
-Internally the S4 brake booster has additional holes on the secondary, output side diaphragm support plate. I am not sure what function these holes play as they appear to be blocked off by the secondary, output side diaphragm when the brake booster is assembled. They may either serve as pressure ports to reduce brake pressure assistance or were there to allow the same component to be used in different brake boosters across the TRW line.
-Functionally the RS5 brake booster *may* provide slightly more brake pressure assistance, regardless it does look nicer and is lighter weight.

I am personally going to utilize the RS5 Brake Booster + Master Cylinder combination to upgrade my B8.5 S4. I have high confidence that the RS5 brake booster does NOT require additional input vacuum pressure from my analysis. Typically the master cylinder, booster, calipers, and ABS system are matched components. At worse; if the booster was designed with a higher input vacuum pressure it would in turn only offer less pressure assistance and would lead to a heaver pedal feel.

If interested please review the photos I took through the disassembly and analysis:

Brake Boosters:
https://photos.app.goo.gl/3uXwDUK9zrTJboTz9

Master Cylinders:
https://photos.app.goo.gl/cQESxESSJNBtekoJ7

[huangrich]

Does anyone install the RS5 MC and Booster in a C7 model?

[Ace]

Sorry. Bringing this back once more.
In case of upgrading from A5 to S5 or Q5(4piston) front calipers.
Would a S5 Brake MC be sufficient?

Didn't do RS5 or sq5 because of it being to obvious and failing tech inspection.