Okay I’m back at home from this springs Ring trip.

Everything was awesome as usual BUT…

Both 996 Turbos we had there from Finland had a mysterious braking problem.

It happened in 8 min laps (= going fast), when braking to a corner the brakes (and thus wheels) lock up for 0.5-1.5 seconds and the brake pedal doesn't lift up to its normal position. Only after that you’re able to steer the car, and trying to avoid a crash in to a barrier. That’s why we had a lot of close calls and we had to quit “the faster driving”….

Both cars had semi slick tires, some suspension mods and 500hp+. Of course we used racing pads from Pagid and Carbopad and racing fluids from Motul and Castrol…didn’t help.

When driving fast a modded Turbo the stock brakes aren’t enough…we would have upgraded both cars brakes in Manthey to GT2-version but they didn’t have any in stock.

Anyway, that’s not the problem because the stock brakes have been quite good with race pads and fluids. Both drivers and cars have quite a lot of experience with their cars on different race tracks. The problem might happen in the beginning of the lap, for example in Aremberg corner after Schwedenkreuz. And that's really strange, how the f*** the brakes couldn't handle a couple of corners

First we started braking sooner and less aggressively but the problem was still there.

So, WHAT THE HECK IS THE PROB?

Have the ABS-sensors gone mad and bad? Of course both cars are driven PSM OFF at the Ring but we found an interesting thing when driving PSM ON, the PSM interfered a lot when it’s not supposed to be… for example cutting the power at 120mph+ when accelerating on a straight line…

ps. Both cars are from 2001 and there's no abs/psm failure light or anything...

UPDATE: New bigger and better brakes and I STILL suffer this problem: https://www.6speedonline.com/forums/...14#post1361114

UPDATE: I forgot this topic for years, anyway, problem solved, various sensors have been changed and they have helped. However, Turbo's ABS is still no race car ABS: https://www.6speedonline.com/forums/...ml#post2742127

 

Did you have a low fluid warning light come on the first time it happened? I've had something similar on stock brakes during DE events. Changing fluid helped my problem, but the light still comes on during the sessions.

 

I've had the PSM cut in at high speeds especially when the car is driving over uneven pavement or undulating roads. It's probably a factor of the car or one tire almost lifting off.

Semi slick tires and a fast track can tax your brakes pretty hard. As for the PSM being intrusive, I would say that Porsche has one of the least intrusive SM systems in the business. A few newer cars (the M3 track model, F430 and Z06, come to mind) have a "track" mode which allow for more aggressive slip angles while still maintaining a good safety net. That's probably the future of SM management systems in most high performance cars.

 

If not an electronic problem, you might want to check out the pistons in the calipers, sounds like they are stuck and need to be cleaned up from rust/brake dust and properly oiled.

 

Over a long period of time there have been quite a number of unexplained incidents(not all resulting in crashes) on 996TT with very much the explained symptons being present. Thread on Rennlist going back some time in the last 2 tears discussed this with a number of posts describing what you had.

 

Hey Kaizu, does it happen on the street when coming to a hard stop as well on bumpy surfaces? When I come to a stop, the pedal goes down as normal, but if I hit a rough patch I can feel it very strongly in the pedal and the wheels lock up for a sec. Dunno if it's the same thing, but it sucks.

 

At nurburgring I experience abs/fluid level light on after 3/4 of the track changed fluid etc. making sure but happens everytime I go to the track. I've checked everything and cannot get it on the street with very aggressive driving only on the track. I've had psm cut in only on out of turns accell but thats to limit wheel spin on exit. I've asked around if there is a temp sensor in the brake fluid system but I get from no to don't know.

 

Thanks for bringing this up to discussion...

First, the low fluid warning light didn't came on, it happened just when we changed to racing fluid. But it happened in a situation where the was a lot of undulation (the fluid level itself was okay). So it was a bit strange but not the reason for this.

Might be the reason Jean, I have heard about a caliper rebuild kit...But still a bit odd though! For example the other car has only 26k kilometers on the clock.

Have not driven that aggressively on the street (yet....got to try this)

Yes the fluid level light might come on with aggressive driving...only on the track, not on the street. There's definately something wrong with the cars PSM because it's cutting power also on the Ring's (a bit bumpy) straight lines after the corners.

 

I had a ton of air in my system when at the track last. I'm installing brake cooling ducting and spindle ducts on my car today, with hopes of curring it by the early june event. If I experience what you did, I won't be using this car for track events in the future, unless I upgrade to the 6 piston yellow brake setup Kevin at UMW sells. Not worth risking my safety...

Mike

 

I have 6 piston gt2 calibers, 350mm disc, gt3 air scoops, and routed air with tube from the front, and drilled holes and removed splash shield and I still get brake fluid level light on the track, I'm trying to figure out if brake fliud movement is triggering the fluid light or it's a temp issue or abs issue. Thanx for bringing this issue up I thought I was the only one with it

 

Upgrade. I'm definately doing it too. But still I'm very anxious to find the reason for my problem...

At Manthey Racing they said that the problem might be with ABS. With stock brakes when you're pushing more than 80 kg of weight to the brake pedal with your feet the stock ABS system stops or might stop working. They said try to brake sooner and less aggressively (and of course bigger brakes help when modulating braking power) but the front wheels still locked up one time when taking a bit sooner and easier braking...and that's when I stopped lapping.

At least the guys at Ring-Racing said the brake fluid movement is the reason for the light...(if the brakes are working okay and the fluid is on correct level.)

 

if both cars suffered the same problem, it must be a problem with the car's prepping. maybe air in the brake lines?

 

Question,

I just bought 6-piston Brembo monobloc front calipers for my car (01 996TT).
Can I expect any brake bias problems since my rears are still stock?

Is there any adjustment that can be done?

MK

 

I have the same set up 6 piston in front rear stock...no issues at all you can even change out brake pads, different compounds and does not adversely effect performance or computer issues

 

It sounds similar to some thing I have experienced early on, hard to explain happens so quickly. almost feels like the fluid is cooked but with a stiff pedal. once I switched to the 6 piston I haven't experieced it again. I posted about this years ago but no one had a similar issue.