I had a random thought today - what if I took my pair of stock calipers + had the pots bored out slightly, then put larger pistons in them? I would make them the same size as an already made caliper so that I could easily get new parts. I would just have to send them to a machine shop to bore out the holes.

If I did this an equal percent on both front + rear then I wouldn't ruin the proportion between F+R.

Then add on a larger master cylinder to compensate the larger fluid area in the brakes.


Thoughts?
As long as I don't go so large that I compromise structural integrity or the caliper itself.

 

What would be your purpose? I don't really see how this would benefit you at all, except the area where the pistons touch the pad.

Also, the rear pistons have the parking brake a mechanism to deal with (which involves the piston)

 

More clamping force = better braking?

 

Bore, hone to size, re-cut seal groove - normally slightly tapered on the seat - and find new pistons, for a one off, dunno, would want to be cheap labour and donating machine and tooling to the cause......

 

Not necessarily. Better braking is from stickier tires. If your brakes already have enough clamping force to invoke ABS, then adding more clamping force isn't going to help as your tires are still the limit. The benefit of larger calipers is to absorb more heat, which is where the benefit really is if you are driving the car hard (i.e. road racing)..

I don't think you'll gain much trying to do this...

 

Well duh. That's a factor that Im leaving out on purpose here. I'm just concerned about the performance of the caliper/rotor/pad itself. Just like I'm leaving out driver skill too.

 

its an interesting idea, but i think the stock caliper isn't the thing that is holding back the stock braking system. you can see that the major change with the 99+ brakes is just a larger rotor.

if you STILL want larger caliper pistons (which might go along with larger rotors and pads, it would probably be simpler/cheaper/better to go with some off the shelf calipers.

 

That's the the thing though- there aren't that many aftermarket kits for the Fc that are basically a straight bolt on and go kit. At least I haven't seen any. I'm sure you can shell out several grand for a been I kit, but why do that if you could modify what you have to do something similar.

Yes I know there's tons of r&d involved in any of this. I'm just kinda surprised this hasn't been tried before.

 

So, you want to do a bunch of custom work to make these oversized piston stock calipers, but don't want to do the simple measurement work to be able to have an adapter bracket made for a new caliper? There really is no crazy work needed to make a BBK. All the adapter fittings for the plumbing are of-the-shelf, as can be rotor hats and rotors.

But really, if you do what you say, you wont get more clamping force by enlarging all these pieces to be equal. You will just end up with the same force transmitted. Maybe you should do some very basic research into how the force is transmitted in hydraulic systems to get why we are all scratching our heads, and why this hasn't been done before. While doing that reading, think about things like pedal travel and brake feel and how that relates to modulating brake pressure control with your foot. It should be eye-opening.

 

Okay. And while I'm doing that you should read the Evo brake caliper to Fc thread and see how it's really not that easy to make a bbk for the Fc.

 

Its always good to think outside of the box, but as others have stated there just really wouldn't be any improvement to the braking system by doing this. The 4pot FC/Fd braking system isnt necessarily inadequate when it comes to braking force. If you need more friction, this can be done with more aggressive pads. The point of most big brake kits is to increase the mass and/or heat dissipation capabilities of the rotor, and to block heat from being transmitted into the caliper/brake fluid.

 

I don't need to, I've already designed one with catalog parts and a custom bracket. It will require no machining except for the bracket to be made (which is simple in 2D). I have friend who sells a miata kit under the same pretense: do some homework and you can find things already made.

I was really trying to help at first, given there are many really well designed pages with lots of explanation and graphics and such that could do a better job than me typing an incomplete paragraph about hydraulic systems. Now, though, I don't think you'd care to hear from me.

 

Stock FD brakes calipers are sufficient enough for most tracks already with the upgrade in pad compounds and slotted/drilled rotors. I personally would either go BBK or leave it stock.

 

You can lead a horse to water....

 

Okay, so that was a dumb question that I didn't think through all the way. I just went to the junk yard and found another pair of from 4 piston calipers (s5) and was thinking, "hey can I modify these to get better performance?"

I applogise for being an ***.

I really haven't seen many kits for fc's - although if they have them for fd's and they make brackets for fd calipers on Fc then I'd assume you could somewhat easily make them fit.

I get much better braking from my 03 a4 than I do my 7. And everyone likes to put cayman calipers on them. Which are much larger than pop cans. I would like to have that much performance with my 7. I already have hawk hps pads and cross drilled slotted rotors.


Any more info on your kit?

 

Ronin Speedworks also sells a kit, although only the fronts.

I've been running one of their prototypes (front and rear) for a few years, on and off the track.

All the kit really does is allow you to use oversized (350z brembo) rotors. I haven't been able to fade these yet with Hawk HP+'s. It's probably the best upgrade I ever did for the car.



And on a past car I had

 

Why not simply get slotted rotors, some performance pads, stainless brake lines, rebuild or replace master cylinder, and make sure your brake booster is in good working order, get better tires and go from there?

Simply trying to get better braking performance from changing the piston bore of the OEM 4piston calipers isn't going to do much.

Improving on a factory brake system means having a larger frictional surfaces.

You need to make sure your ENTIRE braking system is in good working order, and having a good set of tires before you should ever consider anything else.

And comparing your brakes to a newer car isn't a good thing. Remember, you are talking about OLD vs NEW, give it some time, your A4's brakes are going to feel the same once they wear and you'll again, be in the same situation.

 

how wide are your tires? have you bled the system recently?

I still have the stock system on my car and the brakes feel a hell of a lot better than my '01 impreza with the same brake pads. most of that is due to the brake booster though.

 

Only thing I haven't checked is the booster. I'm going to rebuild the whole system because my car has been down for over a year now.

Here's the history on my brakes 1991 s5
Got the car w stock brakes. 2 pot. They were okay, nothing fantastic. I would go down my fav road and after a run and a half they would hear soak enough to not want to drive. So I bought some rebuild 4 piston and vented rear brakes. They came with WBC green and bembo blanks. Thes didn't have the heat soak problem, but when they warmed up the shrieked like a mother. Lottts of pad left too. So I said screw it and got some cross drilled and slotted rotors with hawk hp+ pads. This was better still. And new fluid every time I did something. Making sure there's no bubbles.

But the whole time I had the upgraded calipers it felt a little mushy. When I got my Audi it basically put that feeling in stone. The teams aren't amazing, but it has this amazing initial bite. I love it. And seeing how the brakes are a similar size, but the car is 2x as heavy I'm pretty sure I could get something better from teh 7.


So that's why this thread is here.


Macz those look awesome. But how is the stopping force? And do you notice the added weight of the larger rotors?

 

Desirable braking feel varies from person to person. Personally I prefer brakes with a linear progression, as opposed to ones with a strong initial bite. I like to know how much braking force I'm applying for a given travel of the pedal.

The mushiness you're experiencing is probably due to compliance in the system. For me, this was due to OEM brake lines. After installing stainless lines the compliance pretty much went away. Some people will go a step further and install a Master Cylinder Brace as well, but I didn't feel a need for it.

The brakes on my car stop very well, and even exceeded expectations. With just the HP+ I needed a few events to get used to the new performance and build up the confidence to brake later into corners. After that, I just kept pushing the limits to see if I could fade it, and it took some serious late braking in consecutive corners to do it. I ran Advan AD07's 255/40/17 when this was done.

The rotors are a bit heavier than factory ones, by a few pounds. I didn't notice much of a difference on the track though. In fact, I posted better lap times because of this upgrade. However, if you purchase multi piece rotors from Girodisc, you can bring the total weight of the rotors down significantly, maybe even lighter than OEM. This is what I'm planning for the next car I'm building.

Pads are cheap for FC calipers, which is one of the reasons why we went this route.

 

Yeah somehow I forgot to mention my SS lines. I even got the stock hard lines as well.

And I got a master cylinder brace too. But the car has been down so I haven't tried it yet.

 

I noticed a pretty extreme feel change when I changed from the ABS dual stage brake booster to the non-abs single stage booster. but also re-did all of my brake hardlines to OEM non-abs lines at the same time.

 

I'll probably end up rebuilding the master cyl and the calipers while it's down anyways. Just because I'd like to have everything nice and fresh since its been down so long.

 

not at all, just because your idea didn't turn out to be the "right" answer doesn't mean it was dumb. as we all know, there are only 2 dumb questions, i don't recall the second one, but the first one is "if you carpeted florida how long would it take to vacuum"