My car does the same thing (pedal is soft until pumped up). I think its the rotors cooling and/or the fluid boiling in the pits.

Trust me on the SRF. It does make a big difference when compared to Motul, especially if you are right on the edge of boiling the fluid, which seems to always be the case with our SCs. You will bleed half as often.

Cheers,

Jeff

 

I used to run super blue in my car, and never had a problem. What kind of brake fluid are you using?

 

Never had a problem using SB, pedal always good and firm. Sure sounds like air in the lines to me..

 

Motul 600. Better boiling point than SB. But, you never used your brakes

 

I'm starting to think that as well. I'll have Dan take a look at the system. He's going to have the car for a couple of weeks in August.

 

I'll try the SRF and see if it makes a difference.

 

The only thing that causes asoft pedal(besides a leak) is boiled fluid.

You guys should listen to GWTurboS & Analopg Mike, Stock SC rotors are undersized but the best available. Concetrate on ducting as much air in to them as you can and run at minimum weight. SRF may keep the fluid from boiling but the rest of the parts will still run too hot and as a result won't last long.

 

If it helps you find the material specifications, the OEM rotors are cast from Luperlit.

 

Same here. Something is going with those brakes.

 

And pad knockback.

 

Jeff, what causes pad knockback?

 

If you have a 911, 964 0r 993 w/ stock components w/ pad knockback you have bigger problems than addressed here.

 

There's a nice explanation on Stoptech's web page:

http://www.stoptech.com/tech_info/wp_knockback.shtml

I love this quote about one way to reduce pad knockback:

"5. Slow down and reduce cornering forces
Naturally, this solution is no fun and is not recommended"

 

I don't think knockback will generate heat related problems......rotor cracking and boiling fluid.

FWIW I met a guy at the track that had huge Stoptech brakes on a new ZO6 vette with increased HP, running slicks, and he had a knockback problem.

 

I'm cheating The Man for a couple of minutes while I post this from my office, but this is where all our material specifications books are located and I cannot take them home.

This rotor cracking subject peaks my curiousity based on the category of Why Stuff Breaks. If you are not interested in material specifications, skip this post. This is merely an observation on materials used for passenger car rotors versus what is good for thermal cracking resistance.

My list of gray iron casting grades per SAE J431 says that there are 3 common materials: G7/ASTM A48-20, G9/ASTM A48M-25, and G10/ASTM A48M-30. G9 and G10 have higher Brinnel hardness ratings and lower graphite content, so they tend to wear longer. This makes them popular material specs for replacement brake rotors. However, G7 has higher graphite content and higher thermal conductivity, so it has greater thermal cracking resistance. Unfortunately what I am finding out is that G7 is more commonly used for casting brake drums, not discs.

This makes a little more sense now. The typical aftermarket supplier/manufacturer is dealing with a customer base that is more concerned about wear, not thermal cracking.

I'm jumping back into my regular job right now before I get fired, , but I just spotted a great graph of material tensile strength versus temperature. When I get a moment free, I will post a quick summary as a follow-up.