rbahr

Pad and rotor condition are in very good condition - meaning no odd wear patterns.

My problem is pretty much exactly as described by Darrick. I spoke with him for ~ 1hour, before and after examining my brake system.

Ray

powdrhound

I run the Porsche Motorsport 996Cup ABS on my car. I had it installed a few months ago after searching for a unit for better part of this year. This is one of the best mods I have ever done to the car! The difference in performance is amazing compared to the stock street ABS that comes on the 996/7GT2/3s. It doesn't matter how bumpy the braking zone is or how hard and fast you apply the brakes, the Cup ABS unit just plain works flawlessly. Truly amazing to have confidence inspiring brakes. The stock ABS is great for driving the car up to 8 or 9/10s but the shortcoming become apparent past that, especially if you run tracks that have less then smooth braking zones. Yes, ice mode can be controlled with more gradual brake application but it can still come into play in a panic braking situations or if you end up braking just a little too hard on bumpy surfaces. In the end, you end up with brakes that you can't extract 100% performance out of for fear of ice mode rearing it's ugly head.

With my stock ABS, I had to roll on (more gradually squeeze) the brakes especially if the braking zone was a bit bumpy. Also when braking hard from a high rate of speed while going over a large bump, oftentimes the street ABS had a nasty tendency to go into ice mode (hard pedal with little braking) as the car unweighed and came back down off the bump. The only way to recover the brakes was to release and reengage. With the Cup ABS it makes no difference. I can be hard on the brakes whenever and wherever I want without any issues. On Nittos I see 1.3 Gs under braking with the occasional 1.4G on Motec. There is a noticeable difference is rate of deceleration with the Cup ABS. You can really feel it and it's clearly apparent when coming up on other cars into corners under hard braking. The brakes also feel much better when the car is braking under larger slip angles. It's amazing from simply different programming of the ABS unit does. After all, the hydraulic portion of the ABS is basically a boxster unit.

The only drawback with the Cup ABS is that I'm going through rotors quicker than I did with the street ABS due to the fact that the Cup ABS lock up threshold is higher which allow the brake to work much harder prior to the ABS releasing brake pressure at each wheel. The brake bias also changed with the Cup ABS as the rear brake have a higher lock up threshold which caused more trailing brake oversteer. I used to run PFC 08/11 pad and ended up changing the rears 08 which cured the trailing brake oversteer issues I had. I run the 997GT3RS 380/350 brake system with the larger MC and the 997 cam driven vacuum pump. This set up with the Cup ABS is truly amazing and I've tracked both the 996/997GT3s so I know what those brakes feel like.. If you get a chance get the PMNA ABS unit installed, don't hesitate. The latest PMNA programming is "Diagnostend A02". You will need someone very knowledgeable do the install as the Motorsport ABS communicates via K-line instead of CAN bus, but it's worth it. You won't realize the extent of the shortcomings of the street ABS unit until you drive a car hard with the Motorsport ABS. I don't get overly excited about mods but this was truly a game changer for me.

kk2

I have run almost the exact setup (245 fronts, 315 rears, pfc 08 all around), albeit with none of the rsr parts. I have never had even the slightest inclination of ice mode.

Good luck tracking it down.

powdrhound

One of the drawbacks of the 996 cars that I came across a few years back was the fact that they lack the cam driven vacuum pump that is used on all the 997TT/GT2/GT3s. On the 996 cars, I found that if I transitioned very fast from full throttle to hard braking, I would often times get a hard pedal with little braking. This felt like ice mode but would happen on very smooth surfaces. The symptoms were aggravated at higher altitudes and really hot days when the air was thinner (less air density). After consultation with my shop they told me the problem was a lack of vacuum during the fast throttle to brake transition thus giving very little brake assist (hard pedal, low braking). This was aggravated on hot and high days when air density was even lower thus result in less vacuum. To remedy this, we retrofitted the 997GT2 cam driven vacuum pump to the car and problems were solved. The pump is a direct bolt on by the way. This does not cure ice mode as that is related to the ABS unit, but addresses the other shortcoming of the 996 brake system that sometime get mistaken for ice mode. Obvioulsly Porsche was aware of this problem and corrected it with the cam driven vacuum pump on the 997 cars.

rbahr

Thanks powdrhound,

The cam driven vacuum pump is my next mod. It just displaced the MS LCA - similar to what you have in the rear of your car.

I am very hard on my brakes - but could be harder. That said, I know a few folks with the MS ABS systems, and they are pricey but well liked, but then so is everything else for this beast.

One of the things I spoke to Darrick about was sizing of the brake rotors - he seemed to really like the square setup, as well as pad material to use. Given what I have he liked the 350/350 with pf08's all around...

I have also just finished doing the rear brake cooling mods, got a lot of good information from some of your posts.

kk2: I guess I am just 'lucky'...

Ray

cfjan

What kind of design was the vacuum pump for the 996 cars? Just curious to understand the difference mentioned above.

powdrhound

Here is a copy of a write up I did on the pump a few years ago:

I was at my race shop and had a 997GT2 oil scavenge pump / vacuum pump installed on the car. I am extremely happy with this conversion as there is a huge improvement in brake pedal feel compared to the stock 996TT/GT2/GT3 stock vacuum set up. I have been running the complete 997GT3 RS 380/350 brake system on my car for the last 3 years including the 997GT3 brake master cylinder. Even though my brake pedal has been very firm compared to the previous 350/350 set up, it still did not quite have the same feel as a 997GT3. One of my gripes has been the fact that sometimes when I would transition very quickly from full throttle to max braking, my brakes would not have quite the bite they normally have and braking would require a lot of pedal effort. Basically, what was happening was insufficient vacuum and would manifest itself on very hot days when the air is naturally thinner. I am also at a 5000'+ elevation where the air is even thinner with density altitudes in the summer approaching 10000'. I went over this with the owner of my race shop and it was decided to install the 997GT2 vacuum pump. On the 997GT2/GT3/TT, Porsche installed a separate vacuum pump which is piggybacked onto the drivers side exhaust cam oil pump. On the 996GT2/GT3/TT, brake vacuum is tapped of the throttle body. I am assuming that Porsche added the vacuum pump to improve brake feel and consistency and remedy the shortcoming of the 996 brake system.

The conversion is a direct swap. The exhaust cam oil scavenge pump is removed and replaced with the 997GT2 oil/vacuum pump. The stock 997GT2 vacuum line is routed from the pump and plugged into the stock 996 vacuum line which is just left of the F-hose. It is a direct plug in as the connectors are identical. All that is left is to remove the stock vacuum line that connects to the check valve at the throttle body. We installed a rubber vacuum cap on the stock nipple of the check valve at the throttle body. You also need to install a small rubber vacuum cap on the nipple that goes to the exhaust bypass flap in the 997 cars (you can see the capped off nipple in the third picture). The vacuum caps can be sourced from NAPA. Total time of the swap was about 3 hours start to finish with everything essentially plug and play.

The result of the conversion is profound and makes the brakes feel identical to those of the 997GT cars. Pedal firmness is drastically improved along with improved modulation. This is a huge improvement especially for those that track their cars but it even makes a noticeable improvement in normal street driving. I can see why Porsche decided to go this route on the 997GT/TT cars. For those looking to maximize their brakes, this is a worth while upgrade.

Just to add to this, there are two versions of this pump, a 997GT3 and GT2 version. They look identical but I assume the gearing is slightly different to account for the different red lines on the GT3 and GT2/TT cars.

996TT/GT2/GT3 EXHAUST CAM OIL PUMP
[url=https://flic.kr/p/o5ceja]

997GT2 PUMP EXHAUST CAM OIL/VACUUM PUMP
[url=https://flic.kr/p/omsVFU]

997GT2 VACUUM LINE
[url=https://flic.kr/p/o5aUiQ]

oldskews4

"The result of the conversion is profound and makes the brakes feel identical to those of the 997GT cars"

Does brake feel equal to pedal feel? In all the GT cars I've driven, the 996 GT3 has the best pedal feel by far.

PorscheG96

Very good info. I've experienced the hard pedal in circumstances you describe but not the ice mode.

powdrhound

The 997 vacuum pump made the brake pedal firmer with a more direct bite point. I think in my case the difference was very apparent as I am at a 5200' elevation with summer density altitudes in excess of 8000'

cfjan

Pretty cool.. learn something new everyday! Thanks! How much were the parts approximately?

powdrhound

If I recall, the pump was about $1200 and the vacuum line $200. That was 2 years ago..

Dave S

I too have experienced the intrusive ice mode. I have only experienced this on mildly bumpy brake zones. It can be quite unnerving if you are not expecting it. It was quite problematic at WGI going into turn one and then again going into turn 8. I believe what happens in these cases is that the front wheels leave the pavement for a split second and lock up enough so that the abs thinks there is no traction and so abs relieves brake pressure. In order to alleviate this I apply gentle then quickly firmer brake pressure so the car gets the weight transferred forward which seems to help the front wheels to not bounce off the bumps.
It is far far from ideal and I build in a margin of safety because as previously mentioned if you get into ice mode the only way out is to lift off the brakes completely so the unit resets and then glide onto the pedal again.
Can't believe I'd have to spend 11 grand to fix this. Wouldn't it be great to have an abs reflash solution!!

rbahr

And you can work up a good 'head o steam' going into T1 at WGI...

It is a little disappointing to see this behavior, It existed in my Subaru STi, but at 3x the price point and given the car's design goals....


Ray