Hello all,

I participated in an AutoX event this past weekend and experienced intermittent brake loss. To be more specific, there was no travel in the brake pedal (unable to press the brake pedal). Normal operation would return after letting up and slowing down. This was disconcerting to say the least. I forfeited my remaining runs as I no longer trusted the car, and obviously for safety reasons.

The only mods are a Cobb tune, lowering springs, exhaust, and I was on Hoosier A7's at the time. The car is a 2011 997.2 TTS.

Has anyone experienced this before on the 997.2? I will be scheduling a visit to the dealership but I wanted to get the thoughts of the community as well.

Thanks!

 

Have you checked your brake fluid? This sounds like it could be an issue with moisture in your fluid.

 

I wonder if you need to change your brake fluid.

If it is old,.. or has water in it,.. the fluid in the calipers will boil under hard use.

The resulting pressure will put a drag on the brakes,.. and make the pedal very hard to press, and firm all the way up at the top. (Though the car should be stopping hard at that point,.. unless the pads are also over-temp (brake fade)).

 

Sorry, yes, I should have mentioned that the fluid was changed last November prior to storage for the winter. I did check the fluid level and it looked fine to me.

 

^
>>READ THIS<<

Post #293 is one of the most informative bits I have read in a long time on any of the forums.

 

Post 293 direct link

https://rennlist.com/forums/997-gt2-...l#post14192855

 

Thanks, guys! I just started reading about the "ice mode" issues. I must say that I'm little disappointed, as I was really looking forward to driving on Hoosiers this year. It wasn't until I switched to the Hoosiers did "ice mode" become a problem. In the past I have always used MPSS and most recently RE-11's. Never had any issues with those. I also failed to mention I do have the DSC box installed, so perhaps there is some tuning that can be done there to mitigate this issue as mentioned by TPC-Racing late in the thread. That, or stop jabbing the break as suggested by some, but this method seems to leave some "time" on the table when you're searching for the best time.

 

You must be slightly less aggressive with initial brake application. autocrossing is tough because of the short brake event, but it wont slow you dont much/any once you get the feel forit.

 

The linked post explains the impact of component changes. The lowering springs, tires, and DSC all now work differently than the oem calibration. Not to say it can't be made to work. The OEM calibration is quite front biased anyway.

Things I have seen/tried on our 997.1
Front brake pads
- OEM textar, decent feel, average stopping power
- Ferodo DS1.1 - very firm pedal, very easy to lock the front tires, very hard to drive smoothly, too grabby
- PFC 08 - firm pedal, much more linear initial bite, easier to keep out of the locking/ice mode threshold, and still very powerful

Rear brake pads
- Running Ferodo DS1.1 - rear brakes need more power, and this compound seems to work back here, will try PFC 11 when these wear out.

Front tire size
- If you have track wheels/tires, consider going taller/wider in the front. That has helped for my setup (25.2" front, 25.6" rear). Autocross only though, as the diameter difference at track speeds and long sessions could hurt the front awd clutch.

DSC - try an event without it, to assess the impact.


-

 

Thanks for the tips, Webspoke!

I'm am running CCB's (stock pads), so I assume the pads you're recommending won't work for me, or will they? I'm also using A7's 235/35-19 & 315/30-19, which are 25.6 & 26.1 respectively. The lot we use for AX is VERY bumpy (especially in the turns on that day) and I believe that's where most of my problems occurred. I was also running with PSM off. I would love to run 18's, but I don't think they will clear the CCB's. On track I run RE-11's and never had an issue, bumpy or not, so far.

 

My car even with all the mods does the same on bumpy lots. I just have to brake a bit earlier - away from the bumps, to have the decel done and mostly off the brakes as I turn in. Actually the car seems to really respond to that and you get a very good drive off the corner.

Sorry not much pad selection options for the PCCBs, but if you can find a higher friction rear pad, that will help shift the brake bias a bit rearward, where you have all the weight and big tires to soak it up.

 

You can also swap to gt2/gt3 front calipers that give more bias to rear