netxl

Hello everybody from Germany!
My name is Axel and I just registered. Rennlist has been recommended to me
and I´m very pleased to take part in this community although there is a bit of water in between

Since last year I own a ´96 993 TT and ever since I have trouble with the hydraulic clutch mechanism.
It is leaking now for the second time and I´m reading the threads concerning refitting to MPL Slave Cylinder.
This is a welcome alternative, but I still consider to stick to the hydraulic system (Knee Problem after Motorcycle Incident/ in combination with Performance Clutch)

The question arises with what pressure the Power assisted Slave cylinder is fed? The manual says the system works with 70psi,
but does not differ between pump pressure or pressure after the pressure regulating valve.
I can´t imagine that 70 psi pressure go right into the slave cylinder. My intent is to check the pressure output of the pump and
after the regulating valve before I replace the slave again, just to prevent a third failure.

I hope that you can help me with that issue.
Thanks, Axel

Mike J

There are two pumps on the Turbo that are joined together - one for the steering, and the other for the clutch assist. The feed line from the clutch assist pump seems to feed directly to the slave cylinder but I have not traced it in detail. These slaves are known to fail and are quite expensive, so if you find that for instance there are spikes in the pressure (say due to high rpm's on the engine) that stresses the slave, that would be good to know. Your intention is to put a pressure regulator in circuit then? There is a feed and return line on the slave, so it may regulate its own pressure.

I stripped out the system, put in an MPL, changed over to a NA clutch spring in the pedal cluster, and have been running with that - a bit heavier but I find it perfect, but you do need good knees :-)

Cheers,

Mike

netxl

Hi Mike,

thanks for the quick reply - in my understanding there is a pressure regulating valve (the manual names it that way: No.23)
which divides the system in two circuits.
High pressure from the pump goes into the valve No.23, but what pressure goes from there into the slave via line 13/14/15?

The leakage happened on a track, the RPM was near red line and whilst braking for the turn I wanted to shift down and the clutch was hard right away.

So, it could be that the overpressure valve in the pump got stuck, releasing to much pressure into the prv No.23 or the prv itself is not working properly.
But to see what really is happening, I need to
know the pressure values in the low pressure circuit from the prv to the slave.
The high pressure is 70psi according to the manual.

Cheers
axel

p.s.: The mpl slave with the NA Spring is a good second option. As I understand the other threads correctly, the release of the clutch is very close to the floor, which in combination with higher forces (+plus Sachs performance clutch) might be a problem for my knee on longer trips trough the curvy countryside or in heavy traffic

Kein_Ersatz

Great question, do not know the answer. Your approach of measuring is good.
I do wonder if #23 is a pressure regulator or just a distribution block. As it is not called out in the diagram below as any functional component. I think #9 below is #12 in your KAT diagram.

In case you have not see this:

netxl

Thank you kein_ersatz for the description and the schematic of the slave.

What I really need is the operating pressure of the pump and the confirmation what pressure comes out of the prv to test the system.

Porsche wants to change everything: Pump/Prv/slave

Since it is the second failure in one year I definitely want to know more about the system before I make that decision

Have a nice Day

netxl

Hi guys,

a short update:
I decided to change the slave to MPL cylinder, keeping the original spring and kinematic lever (at the pedals).
I‘m pleased so far, the car is definitely drivable, but needs a strong leg.
Next step is to change the spring and lever to see if there is any change to a „softer“ pedal pressure.

tbc…

Mike J

Yes, good decision - it simplifies the system a lot, and honestly the pedal is not heavy - but then again, i am a pretty big guy. People who have driven the car like the feel.

Cheers,

Mike

Basal Skull

After getting stranded at the track a number of years ago with my second ? Or third hydraulic line failure. I deleted the whole hydraulic system. Got a 964 rs manual rack and MPL slave. Less weight, less to break, and free (some say 15hp) hp!

Kein_Ersatz

15hp, the common unit of aftermarket measurement... LOL!

for me it was 2 replacements of OEM... MPL is a great mod/upgrade to the Turbo.

netxl

Hi rennlister,
after some time driving the turbo I rethink the option of returning to the stock hydraulic clutch actuation. Therefore, I disassembled the slave cylinder as much as possible to get an idea what went wrong.
I found a ripped rubber seal in the piston of the slave (see picture below)
Luckily there is a company nearby which produces all kinds of hydraulic seals and they are very helpful…new seal costs 8€ each
(PM if you are interested in address)
Maybe anyone else can use this information and has the same problem to solve.

The assymetric pin fell out during dissassembling, according to the factory sketch it has to go in that way (see picture)



Make sure to put this pin in the correct way

emreg

Hello Axel,

I was reading your problem regarding to 993T hydraulic clutch system problem. I am having a similiar problem, under similar driving conditions as on high rpms, as I had to chance slave cylinder twice. I was actually very suspicious about the tandem pump, but after reading your problem and some technical documents, I am now thinking that the problem is caused by the pressure regulating valve. I wonder if you solved your problem and I would like to get the name of the company that manufactures seals for the slave cylinder,

Thank you,
Emre

netxl

Hi Emre, sorry to hear that you have the same problem with the slave cylinder.

I still have the MPL slave installed, nevertheless will take out the distributor/pressure regulator next time I get access to it easily and inspect it.

The question imho is that in the english documentation the distributor valve has a different description as in the German manual.
Therefore keeping the question open wether it is a distributor or a regulator. The pump itself has an overpressure valve.

So, I believe that in my case the pump overpressure valve could be stuck open (my pressure lines had to be replaced earlier too) or the above mentioned part has a regulating function which is not working properly.

I do not plan to reinstall the original power assisted slave before I definitely can say what is the root of the failure.

Anyhow, the company which cut the rings is located in Wiesbaden, Germany.

BEKU Dichtringe
Steckenrother Weg 2
65232 Taunusstein
+49 6128 945574

Talk to the owner, he should have the specs on file. If you have any problems ordering, I will gladly assist you.

Take care
Axel

emreg

Hello Axel,

Thanks for your information. I will contact with them.

I am feeling that we are on the same track. However, since the symptom looks like the same, the source might be different, I have come to a point that the problem either with the tandem pump or the prv itself. I actually ordered tandem pump and prv just s while ago. I received the prv, unfortunately I've learned that the pump is out of production. I am still searching for a brand new new one for a while, if someone has in stock by chance. I also ordered a brand new one and a exchange one from Porsche, after a while they cancelled my order due to a dropped part.I also get in contact with some companies if they can repair the pump after logical measurements. As a result, I could not find anyone that will test the pump by plugging on a bench with offical pressures and tell me that the pump is working well or not. They all say "they open the pump and rebuild it"!!. As a result, I am more likely that my problem is with the prv. I replaced the clutch and repair set couple months ago and until then there was no problem at all. The only open point is, since the clutc plate was almost finished, we did not push the limits of the car. After the replacement, it was time to push the limits.

After your information on the forum, I might take a risk and replace the prv and see the result. I haven't decided yet. I will let you know the resut. Regarding to PRV itself,I am also confused about your information if it is a distributor or regulator. I've been thinking of it as well. The only logical thing about PRV as a regulator is that has a return line on the block. Since the system already has a return line, I wonder why Porsche needed to put another return line on PRV. This makes me think that the system is regulated around 70 bar by opening the return line and send the overpressure to the reservoir. If PRV is a distributor then why they need another return line?

Best Regards,
Emre