Hi,
I'm interested in changing how my brake pedal feels in my standard (non GT) Carrera.

GT cars all have that initial firmness (no travel) before engaging the brakes and then there's not overly assisted. Really giving positive feedback as well as allowing you to modulate the pressure. In my car there's travel before engagement and just not the same feel.

I'm looking for how or what I can do to my little old 996.2 Carrera to achieve the same feeling as a GT car. If it is master cylinder, booster, calipers all around then I'm not investing THAT much into chasing this.

Cheers

 

I’m assuming you’ve properly bled your brakes.

I’ve heard good things about the “Endless RF-650” brake fluid and its compressibility.

You could also replace your brake master cylinder with the 997GT3 version. Since your car is a 996.2, I’m not sure if you’ll have to do any special tricks to successfully install this master cylinder. Does your car have PSM?


check out this thread:
https://rennlist.com/forums/996-foru...my-996-c2.html


I, too, complained of excessive brake pedal travel before replacing my master cylinder with the 997GT3 version. The pedal is now very stiff, has much less travel, and requires pressure modulation. The downside is that the accelerator pedal was now much further away from the brake pedal, even when braking hard, that heel-toe maneuvers were difficult to perform. I replaced my accelerator pedal with the Rennline adjustable unit and am happy as a clam after tweaking it to my liking.

 

Hi,
Interesting... I'm finding that when I right foot brake (only when I know I'm going to have to downshift otherwise I left foot brake) my right foot is further / past the throttle and therefore I'm partially pressing the throttle by accident (I have 4E wide feet) My thinking was that if I could have the setup like GT3s I'd have a higher pedal and thus making it less likely that I'll clip the throttle under hard braking. I've also had the luxury to drive a number of GT3 / GT2 cars in the last 10 years (before I bought my 996) and just love their pedal...

I will start with a full bleed and perhaps that fluid before I start down the road of master cylinder. thanks for the tip

 

The Endless fluid or Castrol SRF both will decrease pedal travel by a lot, definitely try a full flush of it. Stiffer pad compounds (yes, literally) will do it as well, but I don't know which ones work besides the Counterspace Garage pads I use in my track car (can be expensive, not recommended for a road car).

If you do all of the easy-replace things right, and the pedal is still sinking, then yeah a larger MC would be in order. My C2 has a fairly stiff pedal though, so unless a previous owner gave me a GT3 MC I think you can solve your problem without it.

 

That statement is very broad and deserves some narrowing down.
If he's replacing brake fluid that has 3% water content and he's running his fluid at close to boiling temp of water with new SRF or Endless, then yes.
However, in that case replacing it with any new brake fluid will have the same effect.

Generally speaking those race brake fluids with even higher dry boiling temps than your regular (street) brake fluids, absorb water from the atmosphere quicker/at a higher rate than the standard fluids.
OK for a race or track car that has its fluid changed at short intervals but after one year in a system they will have absorbed more water and have a lower wet boiling temp as a consequence than a non-race, regular brake fluid.

The difference between GT and non-GT will be the diameter of the MC in relation to the volume displacement of the pistons in all calipers and perhaps the servo characteristics of the vacuum brake booster too (not the case if both use the same part number but that I don't know).

 

No, even if he has brand-new Motul RBF600/660 or Brembo LCF600, ATE Super or some other popular fluids, the stiffness change switching to Castrol or Endless is night and day. My other car is useless on track without one of the two; the brake pedal touches the floor just before lockup. With SRF the stiffer pedal can be pushed on harder and I can actually lock the tires up.

Yes, I know how to bleed brakes, no, the car has no ABS unit to ingest air, nor does it have a booster, no, there's no water in the system as I had freshly flushed everything with some NIB Motul I had on hand. I've personally cycled through every fluid I mention including Winmax BF Racing which is nice and stiff when warmed up but dangerously soft when cold.

 

Thanks for your response, circuit.heart.
I'm astouned to read your observation/experience that srf and rbf yield a stiffer brake pedal when comparing those with a fresh fill of another brake fluid in one and the same brake system.
I can only think of different compressibility at (higher) temperatures to be the cause for your observation.
Do you feel it right away, from the very first applying of the (then still) cold brakes or does it become obvious at warm/hot brakes?

Comparing the datasheets of rbf (couldnt find one for srf) and Ate DOT 4 type 200 (believe it to be successor to SL racing blue) it doesnt list compressibility, unfortunately.
Do you happen to have numbers for any of those as well as Castrol SRF and Endless fluids?

 

The numbers r out there. I use Endless 650 and it has the basically the highest compressability and boiling temp but also the highest price. The reality is all of the higher end fluids r very close and any of them would work.

For peddle feel the 997gt3 mc is the way to go. It just pushes more fluid faster. There is some hard line fitting compatability issues and also the psm (if u have it) needs a work around with a proportioning valve. All of this info is here in Renlist.

 

I've never found a datasheet with compressibility numbers either. I just went by first principles and spent ~$1k flushing cheap and expensive fluid for A/B testing till I had a relative tier list. Yes, the stiffness difference is obvious from cold to hot, and as mentioned before some fluids change dramatically from cold to hot. Motul gets soft after the first hot lap, Winmax gets stiff after the first hot lap which threw me for a loop.

At the end of the day I'm using SRF because Endless is just... too rich for me. Not only is it expensive up front, but theoretically SRF can go longer without maintenance due to its much higher wet boiling point.

 

Thanks, great insight you've provided in your posts. Much appreciated.