Mark Dreyer

Ok, so I've searched the forums and didn't find a thread that addresses this problem so please humor me with some advise.

For the second week in a row I had braking issues at Sebring. What happens is about 20 minutes into the session, my brakes get soft and I have to either drive straight off the course or as in turn 17 yesterday, take a really wide turn, running over cones as I go.

Last weekend I bled the brakes with no improvement. For this weekend I replaced my year old SRF fluid (with probably 6 DE days on that fluid over the year) with Brembo LCF600 fluid (same dry boiling point as SRF, and lower wet boiling point). It was pretty much the same problem as last week.

About my car: Boxster S, pagid yellow pads, GT3 cooling ducts.

I never totally lose the brakes when this happens, and after cool down, they are fine again.

Carlos (from Suncoast region) opined that I probably have a bad master cylinder and recommends I change my stock one out for a GT3 master cylinder. My car has 79k miles, so that's why he speculated that this would be the natural first step in correcting this issue.

Does anyone else on RL have any experience with this issue. If so, I'd love to hear your experience and the fix.

pmgoodwin

I had similar symptoms on my '87 w/ 930 brakes. Turned out to be the seals on the brake pistons.

When the brakes are cool do the brakes engage immediately and the pads don't retract when you let off the brakes? do you find yourself locking up the brakes often?

I rebuilt the front calipers and it made a huge difference. No more fade when hot. the brakes pedal had some travel before engaging and no locking up the brakes. I'll rebuild the rears in the next couple weeks. This should get them for 90% to 100%.

Rebuilding the calipers is simple. I had the calipers cleaned and repainted them so it took a little longer but it is an afternoon to rebuild a pair of calipers.

Paul

garrett376

Too much heat into the system - try a different pad other than Pagid Yellow (which I know 99% of people swear by, but I've found on a stock 996 they go soft part way through races when using Pagid Yellow - this doesn't happen on my car with different pads).

I'd imagine a master cylinder has nothing to do with it if it's heat related... I'd start with different pads.

VERBOTN

Mark:
Stay off the brake

Mark Dreyer

Christian,

Yea, Ron Zita drove my car when he coached me a few weeks ago, so I know where the bar is set, and part of that is I shouldn't be braking as much!

What pads would ya'll suggest instead of the yellows?

VERBOTN

Not sure, I go between yellow and black. Currently yellow to economize on my rotors. I am heading out the 15th and plan on testing a few things in warmup and quali but still have not had the conditions you described, although my car has slightly over 25,000 weekend miles not the nearly 80 you have so perhaps the MS is having issues.

One other question to you HIT THEM HARD or squeeze. I find my car works best when I hit the brakes like I hate them

Mark Dreyer

I hit them pretty hard. I think I'll just replace the master cylinder. It's not that huge of a cost.

smankow

Mark, how old are you rotors? I had a similar problem with my 996 a few years back that cleared after replacing shot rotors. This was after changing fluid.


steve

Brinkley

Mark,

I want to ask you and others to clarify one of your statements. You said, you changed fluid to "Brembo LCF600 fluid (same dry boiling point as SRF, and lower wet boiling point)."

I thought that the "wet boiling point" is the boiling point of the fluid once moisture gets into it, which happens to all brake fluid as it pulls moisture from the atmosphere.?. Therefore, since moisture will always be present you want the highest wet boiling point.

Can you or anyone else confirm this thought process?

Regarding your question, I have always run Pagid Blacks and have never had a problem, running the boxster s since 2004 (DE and/or Race).

himself

I had major cooling problems on my 996. I ended up adding GT3 internal scoops as well as the GT3 brake ducts. Fixed my problem - and I could go back to running Motul.

Here are a couple thoughts on your situation:
1) do you have a non-OEM front bumper? Or is your car slammed? If so, the brake scoops might not be catching enough air.
2) It might be your braking technique. You should have someone in your right seat evaluate your braking. It might be as simply as you riding your brakes too long, and generating too much heat.
3) As I mentioned above, if you need to get more cooling, you can always run pass throughs from the front bumper. I did this on my 996, and it should also work with the 986. Mucho cooling.
4) What tires are you running? If they are not R-comps, you might be overworking the ABS. [goes along with #2]

-td

Gary R.

Wet is determined to be a certain percentage of moisture (what % I don't recall, but it's substantial) that takes quite some effort to get into fluid that is changed as much as most of us do. I don't worry about wet boiling points.

Sean F

as Paul said, rebuild your calipers before you start chasing pads, fluids, master cylinders, etc. this is a common symptom of one or more calipers with seal problem. I rebuild mine every season after chasing the same problem for over a year.

mdrums

Mark you are either overheating the pads (yellows will get a spongy feeling when too hot) or overheating the master cylinder would be my guess. Contact Viper Bob...Bob Brooks....from this forum he would know too. I have his cell if you need it.

Mark Dreyer

Steve, I've put 20K mostly street miles since owning the car and haven't changed the rotors. There are a few little tiny cracks starting to apear at the edge of the holes in the rotors, but not bad enough to change yet from what my mechanic has told me. Is there another criteria to evaluate in deciding to change rotors other than the presence of the little cracks extending to the edge of the rotors?

Mark Dreyer

I have OEM front bumper. Zitza rode with me during coacing session a couple events ago. He had plenty of suggestions but I don't recall any braking criticisms. I bet I'm braking more than I need to though since I don't carry as much speed through corners as Ron does. This past event I ran my street tires since one of my track wheels got bent. Normally I run Sport Cups.