I have been reading about this for the past couple of months. I was ready to either purchase or put together the parts to go to the GT2 setup, but I came across an interesting post.

After much back and forth within the thread I was reading, my take was that if I removed the coupler from the PS pump, the assist would cease to exist, which makes sense since that secondary pump would no longer spin. This would require no changing of any hardware, just stop sending pressurized Pentosin to the slave.

The second part of this is the plumbing. One of the posts made it sound like I did not need to worry about it since the fluid would just remain in the loop.

So, does this sound plausible?

A few specific questions:

1. By doing this, can I improve my clutch feel without changing to a GT2 slave?
2. After removing the coupling, can I keep the loop as is, or do I need to disconnect and plug off the connections?
3. Could the assist be part of the reason this system fails? (My clutch slave on one of my Audis has been there for over 200K miles with no issues)

and finally (a rhetorical question):

What was Porsche thinking when they rigged up this setup? I thought the weird Audi brake assist using the PS Pump attached to a nitrogen charged pressure vessel was unnecessarily complicated, but served a purpose with braking. Why do I need someone's help pushing a clutch pedal? (I agree with the large number of posts that the clutch as delivered on a 997 TT feels inconsistent and requires way to much finesse to not stall or buck at starts)

Ed

 

I also agree that the stock clutch is a pain when starting from a stop—especially for an intermediate speed start: faster than just crawling off the line, but slower than a full-out launch. As for why it was done, once you remove the assist, the pedal force required is pretty significant. Not unbearable, and preferable to the issues with the stock setup, but still more than would be ideal for driving in traffic. Porsche must have figured—probably correctly—that the number of buyers who would be turned off by a very firm clutch pedal would be greater than those who would take issue with the modulation (at least to the extent of not buying the car because of it). Also, it's a lot easier to mod the car to remove the assist than it would be to add it.

I have no idea as to your main question. Since I'm here though, I will mention that the BBI slave is an option if you want to stick with a mostly stock setup, although I would strongly recommend putting in a new (stock) master cylinder while you're at it. I had issues with my install, possibly due to fluid contamination from the master cylinder. Also, however you disable the assistance, you'll want to switch to the GT2/GT3 clutch assist spring, to avoid an unbearably stiff pedal.

 

I have the BBI slave setup. It greatly improves the feel of the clutch, easier to slip etc.

 

There is so much mixed info on this topic, it is really hard figure out what is correct. Last I head was that BBi was causing swollen lines when taken on the track.

 

I haven't had any issues running at COTA

 

I think that was my thread. It seems likely the issue was indeed fluid contamination, but it's difficult to understand how it happened, as the issue occurred on two separate occasions, after completely flushing the system. The best hypothesis I have is that some of the old fluid was trapped in the master cylinder. Since replacing the master and flushing the system again I haven't had problems, but I also haven't had it on the track again yet.

If you do go to the BBI slave, I would recommend replacing your master cylinder at the same time, as well as the cap on your clutch fluid reservoir (with one that calls for DOT4, to be sure pentosin won't be mistakenly added in the future), and make absolutely certain that the system is flushed of all old fluid. It also wouldn't hurt to replace the rubber hydraulic line to the slave with a braided steel one. You can get them from EVOMS (and others I'm sure). You can keep the stock master along with the slave in case you want to go back to stock, to avoid contamination in that direction as well.

I have a separate track car, so I'm not sure when I'll have my 997tt on the track again, but when I do I'll update my thread to confirm whether the new master did indeed solve the problem.

 

That would be great, thank you for the update.

A little bit off topic. I have not made any mods to the clutch system however my pentosin cap ended up swelling and not sealing on the reservoir and spilling out the top leading to my clutch pedal to go directly to the ground. I was in a remote location and Porsche service told me to fill up the reservoir with Dot 4. It has now been 2 years running Dot 4 and i have not had any issues.

However I have not taken it to the track.

 

Wow, that's surprising. On the Pentosin site it even warns against mixing with DOT4. Let us know what happens if you do take it out on track. Even an autocross was enough for me to get symptoms. And it wasn't just the hydraulic line that broke down; even the low pressure rubber line to the reservoir showed signs—you could squeeze it and see the fluid coming right through the rubber.

 

Interesting, my reservoir hose is definitely wet, however I assume it was from the cap spillage.



Come to think about it.. every once in a while I do have to fill up my reservoir, especially after a hard drive. However I have never been able to find a leak. I bet that is because my line is actually swelling and not leaking but causing the fluid to lower!!

 

From my understanding, when one's pentosin cap swells ... the slave is on its way out. Something along the lines of it pushing alot more pressure into the pentosin reservoir because of bad gasket, seals, etc .... and also the cause of the slave leaking as well ...