S3 spongy brakes 6 pots

[8pot]

I am suffering with a really spongy brake pedal on my S3. It has Tarox 6pots with motul 6oo fluid. we have tried differnt servo, abs pump, calipers everything . I did not like the pedal before but have not driven any other S3's to know if mine was unusual. For the record, it is a 200W with 30,000 on the clock. Previous owner was 60 year old woman who did not give it the beans!! It is really spoiling my enjoyment of the car. Do people change the size of the master cylinder as they do with mk1 and 2 golfs?

Thanks

 

[voorhees]

of course

 

[8pot]

What size?

 

[jojo]

I think you must be the only person on this forum with the Tarox 6 pot setup on an S3!

 

[8pot]

Why? Are they no good?

 

[jojo]

Why? Are they no good?

That's the question, no one has them, the preferred setup is the four pot Brembo GT kit, which are basically the same as Leon Cupra R Brembo's. There's a few owners with ECS brake kits using Porsche 996 monoblock calipers also, think these are still four pot?, I don't remember anyone who has a 6 pot setup!?
Did you fit them yourself, the bleeding procedure, if you changed the brake fluid completely, can be a bit fiddly. Requires you to operate the ABS pump with vagcom, and bleed the calipers in a certain order IIRC, that might be your problem?

 

[Dave_Bayern]

6 pots will always cause spongy pedal feel.

You only work out area on one side, so the calcs are:

The standard S3 setup uses a single piston sliding caliper design at 54mm.
So the overall area is 3.142x27x27x2 = 4581sqmm

Your 6 piston setup will have a MUCH larger surface area than this, in fact, even the Brembo 4 pots have a larger area than this.

Its possible your 6 pot calipers have more than double the surface area of the standard S3 brakes.

Now, you might 'think' this is better, but its not, as you only have a limited amount of fluid to move around the system, this is governed by your master cylinder.

You have a 23mm master cylinder, which is WAY too small for 6 pots.

Hence you need to push more fluid in the system and thus it gives you a far longer pedal travel.

You would actually get better braking by going back to the standard Audi calipers.

On the subject of the Brembo GT kit, this also isnt designed for a 23mm master cylinder, ideally it needs 26mm, and in actual fact, the most closely matched 4 pots for the S3 are Porsche Boxster front calipers (996 part number).

 

[Ess_Three]

It's more likely to be a simple missmatch of the pots being too big for the master cylinder.
Most 'big brake kit' makers simply rely of what will physically fit behind the wheels rather than focussing on pedal feel as for lots of big brake it buyers, looks are paramount and pedal feel doesn't count when its parked outside the local wine bar.

I fear this may be the case with the Tarox kits...I can't see how you get enough fluid to move 6 pots from a 23.8mm master cylinder without loosing all the pedal feel.

 

[Dave_Bayern]

Ess - have you just posted a dumbed down version of the thing above where I had to actually use a calculator?

Damn you!

 

[8pot]

any other mastes cylinders compatible that will give me a good pedal. From what I understood, the pistons in the tarox calipers were small and should be OK. The bleeding has been done many times including throufh the VAGCOM thing (whatever that is) could it be something else. We also discovered that the ABS pump for 2000 year was specific to the year. We tried another one and it made no difference (same part number) I am wondering whether the pump was changed due to a poor pedal.
However, is there a bigger master cylinder that will work?

 

[8pot]

Not sure what happened above, missed half my post off!

 

[Dave_Bayern]

You could use another master cylinder, but then you'd need a bias adjustment valve, and to re-run all your lines. It would not be cheap.

The pistons in the Tarox are 27mm and 30mm usually, so WAY bigger than your old single piston 54mm.

Regardless, unless you spend ££££ and change your entire braking setup you will NEVER get a decent pedal feel out of this setup. NEVER.

 

[ChriS3]

You could use another master cylinder, but then you'd need a bias adjustment valve, and to re-run all your lines. It would not be cheap.

The pistons in the Tarox are 27mm and 30mm usually, so WAY bigger than your old single piston 54mm.

Regardless, unless you spend ££££ and change your entire braking setup you will NEVER get a decent pedal feel out of this setup. NEVER.

I thought the Tarox pistons were even smaller than that. The ones on the 10 pots are tiny.

 

[Dave_Bayern]

Tarox website lists them at 26 for the two outers and 30mm for the central piston.

 

[s3ollie]

are you sure you have bled them correctly? i have got 4 pots and they where a pain to bleed right. did you start at the Master Cyl?

 

[Dave_Bayern]

You havent actually read any of what i wrote have you? Bleeding wont help.

 

[Ess_Three]

Save your breath Dave...,
We both know about pot sizes...however, correcly sized brakes that provide feel and enough stopping power to do the job without crippling the already pathetic handling characteristics of most of the cars big brakes go onto, count for nothing in the fashin stakes where 19" wheels and 380mm disks with 12 pot callipers make you King of the plebs.

If, for example, Porsche don't need any more than 330mm discs and 4 pots to stop a 180MHP Sportscar in record breaking short distances, road and track, all day long...why does an S3 with big wheels, a loud exhaust and a silly dump valve need 360+mm discs and 6 pots? Or heaven forbit, 10 pots?
It's all a silly ******* competition.

Personally, I'll take the lightest, most simple solution with least moving parts to corrode and go wrong, that will do the job...and stick my middle finger up to fashion.

Not aimed at anyone in particular BTW, before I get all the cotton wool people jumping on the anti-Ess_Three bandwagon.

 

[8pot]

I see your point. However, I chose the Tarox brakes because with a 330mm disc they fit behind the standard wheels and do not look too flashy in my opinion. I also run standard exhaust but with AST coilovers set at only slightly lower than standard. Essentially it looks standard. I was just after it handling weel and stopping well on track days.

 

[Dave_Bayern]

Yeah, well it isnt going to stop well, you dont have a big enough MC.

I would look into trading them in for some Boxster fronts or similar.