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Clutch 931 slipping at high revs
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Dutch924-racer  



Joined: 23 Jul 2007
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Location: The Netherlands

PostPosted: Wed Apr 21, 2021 5:17 am    Post subject: Clutch 931 slipping at high revs Reply with quote

My 931 clutch is slipping at high revs.

The clutch disc/ bearing is new and the pressure plate is an alu 911 one with higher clamping force.

I already replaced the master and slave cilinder.

I did some adjustments to the rod of the master cilinder but it seems to make no differance may be it even got a bit worse.

Do I need to adjust the pedal spring because of the higher clamping force pressure plate?
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Wed Apr 21, 2021 5:47 am    Post subject: Reply with quote

That's odd. There should be a small amount of free travel in the clutch pedal per FSM. Don't recall the measurement.

Is it happening in higher gears or just lower? Are we sure it isn't wheelspin?


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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Wed Apr 21, 2021 6:38 am    Post subject: Reply with quote

What revs? I would expect slippage either clutch or tyre to happen when hitting full boost and max torque circa 3 to 4000 rpm. By 5000 torque would be tailing off and less likely to cause slippage. I’ve got the non ally 911’plate , 250 torques and no clutch slippage. Road spec tyres however do struggle if I’m being a hooligan
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Wed Apr 21, 2021 3:10 pm    Post subject: Reply with quote

It starts to slip around 4/4500 rpm in all gears. It is defenitly the clutch and not the wheels.

Lower rev no problems at all (also tested very low rev in higher gear but no problem at all).

The problem started earlier, the pedal was not comming back all the way up, I had to use my foot to pull back the last few inches. After that I replaced the both cilinders. That problem is goed niw but also could be the adjustments of the rod.
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Carrera RSR  



Joined: 08 Jan 2010
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PostPosted: Wed Apr 21, 2021 5:17 pm    Post subject: Reply with quote

This is a long shot and my memory is faint, but I recall someone many years ago having a clutch issue on a 931. Found out it was a worn fork + bearing install issue. All had to come out, a new/better fork sourced and bearing seated correctly sorted it.

On another occasion it was found an aftermarket relined clutch plate + reusing the old pressure plate was at fault. It was fixed when a new Sachs clutch and pressure plate was installed.
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Cedric  



Joined: 27 Aug 2004
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PostPosted: Wed Apr 21, 2021 5:19 pm    Post subject: Reply with quote

Did you build everything to s1 spec then with s1 flywheel etc?
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Thu Apr 22, 2021 2:43 pm    Post subject: Reply with quote

It is all S2, flywheel, etc. The fork, axle, sleeve and bushes are all new.
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Cedric  



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PostPosted: Thu Apr 22, 2021 3:50 pm    Post subject: Reply with quote

But i didn't think the 911 pressure plate fit the s2, which one did you use? Do you have a pic on pplate?
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Carrera RSR  



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PostPosted: Thu Apr 22, 2021 5:09 pm    Post subject: Reply with quote

C�dric wrote:
But i didn't think the 911 pressure plate fit the s2, which one did you use? Do you have a pic on pplate?


+1 was my thought. Assumed the 911 pressure plate was only for S1 spec clutch and flywheel? May be wrong. I binned off all my S2 parts to only use S1 spec on my engines to avoid any future issues
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Cedric  



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PostPosted: Thu Apr 22, 2021 6:35 pm    Post subject: Reply with quote

Carrera RSR wrote:
C�dric wrote:
But i didn't think the 911 pressure plate fit the s2, which one did you use? Do you have a pic on pplate?


+1 was my thought. Assumed the 911 pressure plate was only for S1 spec clutch and flywheel? May be wrong. I binned off all my S2 parts to only use S1 spec on my engines to avoid any future issues


The s2 share the clutch with 944 and 944 s2 instead , which are very different. The pressure plates have very different depth since the face of the s2 flywheel is deeply recessed.
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Carrera RSR  



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PostPosted: Thu Apr 22, 2021 8:52 pm    Post subject: Reply with quote

C�dric wrote:
Carrera RSR wrote:
C�dric wrote:
But i didn't think the 911 pressure plate fit the s2, which one did you use? Do you have a pic on pplate?


+1 was my thought. Assumed the 911 pressure plate was only for S1 spec clutch and flywheel? May be wrong. I binned off all my S2 parts to only use S1 spec on my engines to avoid any future issues


The s2 share the clutch with 944 and 944 s2 instead , which are very different. The pressure plates have very different depth since the face of the s2 flywheel is deeply recessed.


My guess is that the 911 pressure plate + S2 clutch + S2 flywheel is that the 911 PP is not using its full clamping force onto the clutch and flywheel due to the flywheel being more deeply recessed. It just can't push hard enough, that deep.
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Carrera RSR  



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PostPosted: Thu Apr 22, 2021 8:59 pm    Post subject: Reply with quote

Solution is S1 spec flywheel + clutch + 911 ally pressure plate

Or

S2 spec flywheel + S2/944 spec clutch + S2 spec pressure plate not 911 ally with higher clamping force

I know went with first solution but with steel 911 PP, which was some kg lighter than the old 931 steel PP and the 911 version had 30% more clamping force. No issues in quite some years but I fear the clutch plate should be nearing its lifespan now from aggressive hill climb starts and shifts.

I looked at buying the ally version but was told it could only be bought as a complete 911 clutch kit at circa €1000? IIRC.
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Dutch924-racer  



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PostPosted: Fri Apr 23, 2021 2:42 am    Post subject: Reply with quote

There are two types of S2 flywheels, I have both, one is suitable for the 911 pressure, the other wont fit because the 911 pressure plate has a raised disc. That other flywheel uses a different clutch and pressure plate (same as 944 S2) , the pressure plate disc is not raised with this version.

I will look for some partnumbers and pictures to clarify.
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Forge recirculation valve + boost controller
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Cedric  



Joined: 27 Aug 2004
Posts: 2600
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PostPosted: Fri Apr 23, 2021 5:41 am    Post subject: Reply with quote

Dutch924-racer wrote:
There are two types of S2 flywheels, I have both, one is suitable for the 911 pressure, the other wont fit because the 911 pressure plate has a raised disc. That other flywheel uses a different clutch and pressure plate (same as 944 S2) , the pressure plate disc is not raised with this version.

I will look for some partnumbers and pictures to clarify.


It hink the weird s2 hybrid version was for the US market only.
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peterld  



Joined: 10 Dec 2006
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PostPosted: Sat Apr 24, 2021 8:38 pm    Post subject: Reply with quote

There are indeed several versions of the S2 flywheel.
ROW from day one got the stepped version used in conjunction with the dual mass (rubberised centre) clutch plate; however in the States the early S2 had a normal flywheel, but with the metal insert for the trigger count, and outside teeth. #931 102 206 01
I too use one of these with a SPEC 8 puck clutch plate.
Later S2 production for the USA was similar to the ROW setup.
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