23mm brake master cylinder, anyone using?

[goofycarp]

Hi, is anyone using a 23mm brake master cylinder and any noticeable brake difference. Also any favorite brake pads for street? Trying to maximize braking on a 70T without big and expensive conversions. Thanks. Cort.

[Gburner]

Hi, is anyone using a 23mm brake master cylinder and any noticeable brake difference.

Yes noticeable. I had a 19mm M/C and my car stopped very well. What I did not like was a brake pedal with more than 2 inches travel that felt vague and mushy, even more so more when the brakes were hot.
By installing the 23mm M/C I now have less pedal travel and much better brake pedal feel. It is much easier to accurately modulate the brake pressure when you have less than an inch of pedal throw. Now the pedal feels firm, not mushy. The larger M/C will require a little more effort to achieve the same hydraulic pressure as the smaller M/C. Consistent performance braking is not about pedal travel, it’s about modulating pedal pressure.

I use Pagid Orange pads for a 90% track use 911. They would not good choice on the roads. On a freeway drive they cool off and don't bite well until they get hot again. Then again they have been great at the track, no fading or boiled brake fluid.
I think Pagid makes a Blue pad preferred by some of the street/track guys like.
Try some of the super blue brake fluid too.

[ttweed]

Keep in mind that Gburner is running 930 brakes on his car. A 23mm MC is useful in his application because they are 4-piston calipers that need to move more fluid volume to work. If you are talking about changing your MC without upgrading your brake calipers, that is not a good idea. Play with the pads, fluid and cooling and keep the 19mm MC.

I have heard great things about the Hawk HP+ pads for the street, but haven't tried them yet. I use Pagid Orange for the track and cheap Axxis Metal Master pads for the street at the moment.

TT

[Gburner]

Very good points TT , and I should have mentioned the 930 brakes.

[Jol Dantzig]

Tom, that's correct about the volume needed for the 930 brakes (this is the set-up I have in my 914-GT and it works GREAT) but I wonder what would happen if you DID put one on a smaller caliper set-up.

Anybody tried this?

Jol

[ttweed]

I wonder what would happen if you DID put one on a smaller caliper set-up.

Shorter pedal travel, with a much harder pedal (more leg effort required to generate equal pressure). It is a pressure vs. volume thing. The diameter of the cylinder determines how much fluid is displaced per stroke (given the same lever arm depressing the piston), and this is also related to how much force is required on the pedal to reach a given hydraulic pressure in the brake lines and at the caliper pistons (which results in the clamping force on the rotor by the pads.) A bigger cylinder will displace more fluid, but at the expense of pressure generated for the same stroke force. Thus, as Gburner said, his change to 23mm resulted in a firmer pedal feel (more force required at the pedal to generate equal pressure in the lines) and a shorter stroke (more volume for equal pedal/piston travel.) Many people think that this gives a better "feel" to the pedal and is easier to modulate. I think there is a limit to this, though, and too big a cylinder on too small a set of calipers would give you such a short, "rock-hard" pedal that it might be difficult to adjust to it. It's a matter of personal preference, though, and one could probably get used to it, I have just never heard of anyone doing it. The Porsche engineers were pretty astute in the braking department, and have generally provided a pretty good match in the stock brake systems for most driver's expectation of how the brakes should "feel."

When I upgraded to 930 brakes on my '73, I bought a 23mm MC but I have never installed it. I am still using the original 19mm cylinder, and the brake pedal travel is long, but the pedal effort is low. It is a different feel, but you can adjust to it. You have to be delicate with your foot, because it is easy to generate too much pressure and lock the wheels up if you stab the brakes hard (which you shouldn't be doing, anyway!), sort of like having power-assist, except you also have to push the pedal further to get into that range of high pressure. As I get deep into a 20 or 30 minute session on a hot day at the track and the fluid heats up, I can feel the pedal getting longer to maintain the same braking pressure, but I have never run out of travel yet. I have good cooling to the calipers, and between sessions, the pedal shortens up again as the system cools down. If I were going to run an enduro or something, I would definitely install the bigger MC, and eventually I will do it just to get the part off the shelf in my garage (along with the alloy crossmember next to it that I never put in) and learn to drive it with a shorter pedal and more leg effort.

TT

[72targa]

I got to sit in a 956 one time and one thing I remember was that there was NO PLAY in the brake pedal!...

[Jol Dantzig]

Tom,
Your explanation makes perfect sense, if I had thought it through I would have realized the results that I encountered before I changed the MC had demonstrated exactly what you described.

Jol