I helped a friend with similar symptoms recently, on a 02 TT. Behaved exactly like you're describing - pedal stuck after inspired drive, however it loosens when you "pump" it a few times.

Would also like to know the answer to this.

*subscribes to thread

 

Oak,

Man of knowledge: did you change out your rear calipers and or rotors?

MK

 

I guess it's called learning the hard way, lol. I did change out the rear rotors and calipers, but I think they are the same as stock. still 13" diameter but the calipers are now yellow. I had the crew from bydesign change them out back in glory days. I think it was a complete kit, not sure who they had sourced it from.

 

I have now all new braking system (GT2 6-piston, GT3 Cup brake cooling etc etc)...And I still have experienced a couple of times this problem! It sucks!!

It happens usually when I'm doing a gentle braking for example:
- because of cars ahead and gotta slow down a bit
- because I'm overtaking cars on corners (and thus twisting the steering wheel while braking so the brake balance is far from optimal.)
- I'm starting cooling lap
- I'm turning to the grid from the track

No one knows what to do...

We have gone all the way to Porsche Germany with this problem. They said that it might be the valve for brake pressure. The valve wouldn't work normally if the car's lowered too much and driven hard on semislicks...sounds a bit crazy and I really can't explain it more detailed.

Anyway I really doubt that's the reason because now my friend has a very slammed Turbo and he hasn't experienced this problem anymore with the new similar brakes. And he has driven a lot of track. And with the old brakes he locked up quite badly, also one time on the street while driving normally.

So feel free to comment...
Anything is appreciated.

 

mmmm, Bizarre!

I'm not having issues like this, can it be anything to do with the ABS sensors, I know on some of the Euro Turbo race cars they have had different sensors (I'm also sure I read this in an article) You havent kept your shims in between pad and piston? (nothing to do with what issues you are having)

 

Just for completeness, I would measure the rolling diameters of
all tires, very carefully.

 

also Warped disc, possibly joe?

Could be grabbing on!!!

 

Amazing... I have "fixed" my issues with 3inch front ducts to spindle mounts, and 2inch rear ducts to spindle mounts, along with fresh fluid I bleed before every event, along with Pagid Yellow pads and factory stock 13inch rotors. So far three days hard driving in heavy traffic at VIR have proven to be "do-able" with an instructor commenting how my brakes work better than those of BOTH his race cars...

Mike

 

I think Stevo was probably on the mark then. More cooling means no warping.

 

Good to know that you guys made it out of the ring with no harm. Hope you find the cure to your cars. Good luck !! Cannot imagine how bad a track event would feel, after getting into such problem. I would go for an aftermarket brake kit, inorder to ump that problem.
Good luck on your next trip, and be safe.

 

Thanks, actually, this spring the other Turbo I was talking about crashed on the Ring because of this problem. And everyone is quite amazed of the problem, for example I have had 3-4 different drivers on the passenger seat and they all have witnessed this problem, so I'm not making this up...

I already have new aftermarket kit...And the brakes have still suddenly locked up. It's because of ABS or brake pressure or something like that.

The next easy thing would be changing to racing ABS. Too bad the racing ABS used in GT3 (Cup) is completely different and cannot be used in a 4WD Turbo. Will see what I'm able to do. I've driven enough track days this year (and the weather is getting colder, and actually I'm too busy) so solving this problem for the next spring is on my wish list...

Even though some braking problems, I wasn't taking it too easy at the Ring (I was just braking early...). I did many 8.00 laps (with PerformanceBox) with traffic....Highest speed in Scwedenkreuz was 260km/h on the GPS :O (For example CGT by Horst von Saurma / Sport Auto did 259km/h there when he lapped there 7.3X lap...)

 

If your wheel diameters are off front to rear by more than 5mm you will get this problem. What size slicks were you running on the front and on the back?

Dr John

 

Toyo R888 225/40/18 & 295/30/18.
As new these tires have the correct diameter.
Of course the rears go more quickly but I doubt that diameter difference.

Now I think I should go through some brake bits before the season really starts.

The problem should be within the ABS computer, pump or sensors (not disks, pads, calipers etc. because I have already changed them.)

 

Hi Kaizu, Have you done anymore or found the problem with the ABS?
I am looking to fit the Cup Car ABS to my T/T, but need to access schematics to work it out.
Have you seen the motorsport ABS unit listed on the Bosch website?

 

I believe there could be issues when you are heel/toeing on downshifts with the Fly by Wire Throttle set-up of the T/T's.
My T/T is a race car and currently runs the GT3RSR brake set-up incl the 2 master cylinders and no ABS, PSM etc.
I have experienced several unexplained brake lock-ups, usually when heel toeing on a down-shift.
It appears sometimes that the throttle doesn't respond when you blip the throttle while braking, thus resulting in rear wheel lock-ups.