Spyerx

holy crap.

So basically brake, a second later likely when near lockup, the rears lock up, and a front locks up. Outside of failure of the ABS unit...speed sensors are working obviously. I'm wondering if the condition is similar to what Jaybird describes and is some sort of mode in the ABS unit caused by an imbalance situation. Ice mode is similar ot this, the ABS thinks it is sliding so it limits force as ABS doesn't really work on ice... but ice mode is a rock hard pedal and no stopping force.

How repeatable is this condition for you? I'm wondering if you got out of brakes and back in, if the condition would stop itself similar to ice mode.

Pads F - RS29
Pads R - RS29
Rotors F - Gyro
Rotors R - stock drilled
Wear of all?
TC on or off?
PASM on or off?
Are you hitting any kerbing at point of braking or during braking? Hard to see in video.

Keep in mind that different rotors and makes of rotors have different friction levels, on my car I basically ran OEM (or cup) or Brembo and matched pads F/R. These cars I found can use a little more rear bite/bias so I changed rear to a type3 rotor and ran type5 in front with the same RE10 pad compounds.

I also found that overly 'bitey' pads didn't work well for me with R compound tires, they just didn't play nice with the street ABS, so an endurance pad like the RE10 and others had plenty of bite and had the benefit of lasting a long time and easier on the rotors than sprint pads.

You can actually see the ABS working, so it's not a full ABS issue, so wondering if it is related to the combination of pads, rotors, tires, and track condition here that is triggering this mode with the ABS.

JJE997.2RS

Might be the pads. That’s exactly when it happens. Hard braking after a straight.

But RS29’s are a pretty popular track pad option for RS’s... I’m not the only one running them or that has run them.

That is what concerns me

I didn’t push it much after and that was really the only time I really got on them. When they behaved like that I was much lighter on brakes rest of sessions.

obviously would like to activate ABS and have it work...

new pasa sound much much cheaper than a new abs pump.

Jaybird33

For what its worth, when I first installed Hawk DCT70 pads everything worked fine, then a couple track days on the pads the ABS problems started. Since the pads worked initially it ended up being the last place I considered. I also used the DCT70 on a Boxster Spyder without any issue, albeit on Girodisc rotors. Some people may have good experiences with the RS29, but due to any number of variables (rotors, track, wheels, breaking style, etc.) your car may not like them. Like you said a pad change is a lot cheaper then a new ABS unit.

flsupraguy

Never had anything remotely like that on my 997.1 gt3 and I'm hard on the brakes on turn 7. Weird.

Sword_of_the_Spirit

Darn. As mentioned prior, disk/pad coefficients are key. Also, your balance between f/r tire ratios is also important. Sometimes, these street units trigger when a bump or ripple is felt by the ABS. Entering the Cork is a good example for Laguna.

I’d hookup to the Porsche diagnostic and cycle that sucker a few times to make sure any faults are found as well as old fluid that isn’t pushed out through pressure bleeds.

Ferodo’s are a nice choice if looking elsewhere.

JJE997.2RS

Thanks for responses.

stranger still is that those rs29’s are an enduro pad.

80% life left on tbem
front rotors pretty new
rear rotors original

Going to have to take it in and check for codes in ABS system. If none, then new pads

i hated the DTC70’s in my race car. Went to Gloc’s and never looked back.

cunno

This happened to me at Spa looks similar. The only thing I found was the battery terminal was lose, believe abs system lost power and had a melt down all 4 wheels locked up and flat spotted. Reconnected battery and not happened again.

JJE997.2RS

Yikes man. Scary. Wish it was something that simple...

So far what I have deduced:
1. It's not normal
2. Really hasn't happened to anyone else
3. It's not tires
4. Could be the pads being too aggressive (though I highly doubt this as they have been used before)

I am going to try and bring it this week to see if diagnostic says anything.

Thanks

Stig_997

Have you found out what the issue was?
I had this same exact issue early this year, but I had just bought the car and was working through a few adjustments. After that I did 2 track weekends with no issues. Then this weekend at COTA the car was perfect on Saturday, but on Sunday morning, first session, rear left wheel locked on me three times. 2 on the out lap (at a slow pace) and 1 braking into T1 in the first lap. Rear left locked again and sent me into a 360deg spin. Luckily I noticed the issue on the outlap so I was at 70% of my normal pace when it happened.

Car is a 997.2 GT3 with the same exact rotors and pads as you, so I'm very interested in the outcome.

Thanks,
Steven

Socar37

I know its been couple years on this thread but I'm having same issue. COTA Turn 12, 20 and others. 1 tire/2 tires. ABS locking. MSR ABS locking up FR RR. Anyone ever get any resolution. Im getting no fault codes. Happened with 18 and 19" tires. OEM size 19" tires at COTA. 18" tires i spun with are 1.1" vs OEM Tires 0.7" taller in rear.

Gyrodisc rotors front and rear. Pads are PFC. Issue occured at COTA in July and MSR in Dec but not at Eagles Canyon in Oct. Strangest thing.

JJE997.2RS

I just replied via PM.

I never resolved or found the issue. I actually havent tracked the car since then. I am putting stock pads back in and will give it a shot.

Pretty brutal. I'm sorry it happened to you as well.

Jero

Belinko

I suggest you read through this thread. Draw your own conclusions, some really good information, but maybe it's not applicable, but sure sounds like it to me.

https://rennlist.com/forums/997-gt2-...got-me-21.html


Originally Posted by Steven_S
Hello Everyone,

I've been hesitant to chime in on this thread, but the speculation and misinformation has reached a point that I feel I must respond.

First my background: I am a senior chassis control engineer at Bosch with 17 years of experience calibrating ABS, TCS and VDC (stability control). I started tuning ABS in 2000, and worked extensively with ABS calibration on the system that is installed in the Porsche 997 variants. I also know many of the Bosch engineers in Germany who work on the Porsche projects.

I recently saw this thread after purchasing a 997.2 GT3 and joining Rennlist. In fact, there is a reference earlier in the thread to an ABS article I wrote for the E30 M3 community back around 2003 (Post 118 by Stuttgarter, who was a former colleague of mine). Unfortunately the link no longer works, but I will see if I can find it and repost.

Here are the main items I want to clarify:

Ice mode: Whenever I hear this term, it’s usually in reference to poor deceleration upon initial braking. There are three main causes for this:

1. Component changes (tires, pads, rotors, suspension parts)
2. Tuning strategy to meet customer specifications on ice and snow
3. Driving style (timing and rate of apply)

Erratic ABS behavior such as bump sensitivity or wheel lock: mainly caused by component changes that are incompatible with the production calibration (see #1 above)

Component Changes: When tuning projects for series production, every component on the vehicle contributes to the performance of the entire system. It’s not uncommon for manufacturers that have very high performance expectations (like Porsche) to request an ABS or stability control retune for a small design revision from the tire supplier. This could be something like a slight change to the compound composition or cord structure ON THE SAME design/size OEM tire. Think about that when you are installing oversize Hoosiers on your car.

Same thing with pad/rotor changes – the controller is no longer tuned for optimum performance with a pad/rotor interface that has different friction coefficient and apply/release characteristics.

Also think about suspension changes like dampers, springs, and even bushings. The ABS, TCS and stability control are no longer optimized for a vehicle that now has different weight transfer and suspension articulation characteristics from the OEM spec vehicle.

To summarize, the OEM ABS, TCS and stability control tune becomes invalid when installing aftermarket tires, pads and suspension. Even slightly different tires and pads could be enough to reduce robustness of the system performance. It’s a testament to the robustness of the Bosch system that it works as well as it does under these circumstances.

Tuning strategy to meet customer specifications on ice and snow: All manufacturers have requirements for ice and snow performance for road cars. So the ABS, TCS and stability control have to provide optimal performance for ALL surfaces. The purpose of the logic development and tuning process is to maximize performance on each surface, with the least amount of compromise for other surfaces. Obviously this is very difficult, requiring fine tuning to achieve all of the OEM performance goals. This is the reason why component changes can have large effects to the robustness of the system.

Driving style, especially with modifications: as mentioned above, many of the modifications made for track use result in much different wheel dynamics that the controller is not optimized for:

• Sticky tires: Mue/slip curve is much more “peaky”, meaning the tire tends toward lock very quickly when exceeding the linear range of the curve.
• Track pads/rotors: higher coefficient of friction and “bite” result in faster wheel lock at lower pressures.
• Stiffer suspension/dampers/bushings: slows load transfer and build-up of normal force, resulting in earlier wheel lock during quick brake applies.

All of these mods cause the tires to slip faster during braking than the controller was tuned to expect for dry pavement. Now add in an aggressive driver who spikes the brakes at initial apply and the tires will tend toward lock very quickly before the vehicle builds much deceleration. The controller will release pressure to recover the tires (prevent deep slip/wheel lock) and the driver feels the lack of deceleration as “ice mode”.

So if you want to avoid ice mode on a vehicle with heavy modifications, the best recommendation is to slow the initial apply and then quickly ramp in pressure after the initial weight transfers occurs. This is proper braking technique to prevent wheel lock for non-ABS cars as well.

There are additional situations that can contribute to ice mode, such as bumpy surfaces, and aggressive turn-in during braking. Remember the primary goal of ABS is to prevent wheel lock so the driver can steer. The only way to prevent wheel lock when the tires are skipping across a bumpy surface or the inside tires have no load is to RELEASE PRESSURE. The pressure loss will be proportional to the time the unloaded tires have no grip. ABS braking performance in these situations is usually not a problem with an OEM spec vehicle, but track modifications will affect robustness.

The Motorsport ABS controller works so much better for track driving because it is optimized for race tires/suspension and has a selector switch for different surface conditions such as rain, cold tires/cold pavement, hot tires/hot pavement. Ice/snow performance is not even considered. Obviously this is a much more robust solution for track only driving in a modified car if you have $10k to spend. Just don’t try driving this same car on a snowy mountain pass…

Additional Warning: Under NO circumstances should you try to defeat the ABS system by pulling a fuse, unless you install mechanical rear brake proportioning. You will lose EBD control, and lock rear the rear wheels before the fronts in almost every situation. Very dangerous.

Steve