sergiDA

Hi:

I am having a problem on the brakes of my 964. every time I go on a track day, after 15´of running the pedal goes down and it doesn't brake any more, I need this to cool down and then it will work again but it won't be the same anymore during the rest of the day.

I am running with drilled disk, stock calipers, Yellow Pagid pads, Castrol SRF liquid and metalic tubes... I though my set up was the correct one for track days, but may be i am wrong?

Thanks for the advise.

Steve Weiner-Rennsport Systems

Hi,

Some additional info is needed to help diagnose the problem.

When the brakes fail, does the pedal go from being firm to being soft?

After its cooled off, does the pedal height & firmness return 100%?

How old are your brake lines?

One of the very first things I'd do is check the peak operating temperatures of the rotors using temperature indicating paints. Thats a critical bit of information as you may be exceeding the temp range of your Yellow pads.

sergiDA

hi steve:

Thanks for the answer.

yes the pedal becomes soft.

after they have cooled down, the pedal height & firmness return 100%, but this time the problem starts earlier than before.

not sure how old the brake lines are, I don't think more than 2 years, as the previous owner is the one who started with the upgrades, and sold it to me last november.

Regarding the scientific aproach you are proposing this is all very correct, but I am not technical enough to go through that process and on top when I return to the track I would like to have a solved problem.

What would be your diagnose, may the yellow pads do not stand the track temperature?

thanks in advance.

mkd944

Or maybe your brake fluid is overheating or your lines are expanding or both. How fresh is your brake fluid?

sergiDA

the brake fluid is 2 weeks old and the brake lines are metallic and I think 2 years old, so in theory they should be good enough...

boxsey911

You say your calipers are stock...do you have a C2 with the small rear calipers? If so, it is likely that the small rear pads are the ones that are over heating. This happened to me before I upgraded to the later 4 pot calipers.

sergiDA

I supose my rear calipers are stock therefore small rear calipers.

When you upgraded to 4 calipers that means that front and rear rotors and calipers will be the same size? don't you need then a devise ( Tilton or similar...) to transfer more brake to the front...

Thanks for all your help

Rocket Rob

The factory changed the brake bias valve when they changed from the two piston rear calipers to the 4 piston. If my memory is correct, they went from 45 bar to 55 bar. I installed 4 piston calipers on my C2 and I changed the bias valve. Its a simple change.

Rocket Rob

More about the bias valve. https://rennlist.com/forums/964-foru...-calipers.html

boxsey911

And to just add to the advice already given by Rob, you don't need to change the rear rotors when installing the 4 pots.

The original rear 2 pots have very small pads, so they concentrate the heat when on track. The other benefit of switching to 4 pots is that you get a much wider choice of pads to use (they're the same pads as used in the front calipers).

ThomasC2

If you're not sure what you it's easy to check. If you have the 4 pot cailpers in the rear they look as exactely as the front calipers. The 2 pot version is more round in it's shape and smaller.

Thomas

race911

Steve (as always) nailed it. As I suggested to the guy in Australia who had similar a few weeks ago, you have to know what your operating temperature is. Temperature paint is easy beyond belief. Plenty of guys tracked pre-'92's the first couple of years the cars were out, and they worked. I had a soft pedal in my RSA Tuesday at Laguna after the first session, quick bleed and all was fine the rest of the day. (It had not been bled since last fall.)

Bottom line is if you're not technical enough to understand what's going on (and believe me, it isn't that hard to wrap your head around), then find someone who is. The car (body) you save may be one of your fellow track enthusiasts................

swftiii

Sergi,

I am running almost the same setup as you. As others have mentioned, I upgraded the rear calipers to the same ones that were on the 1992+ C2 - they use the same brake pad as the front, but the rotors do not change. With this the bias valve needs to be updated to the 1992+ as well.

The only other difference in my setup is I am using Porsche Genuine solid rotors.

I had similar issues when I was running PFC97 brake pads and after a lot of research bit the bullet and moved to the Pagid Yellow RS29s and have not had any brake fade issues since.

Steve and others - Although my brake issue has been resolved, I'm considering playing with understanding the temperatures I'm seeing in my brakes - what paint/strip would you recommend and what temp range?

Thanks,

-Skip

race911

http://www.pegasusautoracing.com/pro....asp?RecID=862

Steve Weiner-Rennsport Systems

Skip,

This is the one I use:http://www.essexparts.com/shop/other...mal-paint.html

I put 3 short strips of each paint on the outer edge of each rotor to show me peak temps. That allows me to chose the proper pads and fluid for the car and its driver.