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Dutch924-racer
Joined: 23 Jul 2007 Posts: 1076 Location: The Netherlands
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Posted: Wed Apr 21, 2021 5:17 am Post subject: Clutch 931 slipping at high revs |
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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? _________________ 937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller |
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Rasta Monsta
Joined: 12 Jul 2006 Posts: 11723 Location: PacNW
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Posted: Wed Apr 21, 2021 5:47 am Post subject: |
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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?
_________________ Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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Carrera RSR
Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK
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Posted: Wed Apr 21, 2021 6:38 am Post subject: |
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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 _________________ 1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Dutch924-racer
Joined: 23 Jul 2007 Posts: 1076 Location: The Netherlands
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Posted: Wed Apr 21, 2021 3:10 pm Post subject: |
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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. _________________ 937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller |
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Carrera RSR
Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK
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Posted: Wed Apr 21, 2021 5:17 pm Post subject: |
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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. _________________ 1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Cedric
Joined: 27 Aug 2004 Posts: 2600 Location: Sweden
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Posted: Wed Apr 21, 2021 5:19 pm Post subject: |
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Did you build everything to s1 spec then with s1 flywheel etc? _________________ 1980 924 Turbo
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Dutch924-racer
Joined: 23 Jul 2007 Posts: 1076 Location: The Netherlands
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Posted: Thu Apr 22, 2021 2:43 pm Post subject: |
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It is all S2, flywheel, etc. The fork, axle, sleeve and bushes are all new. _________________ 937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller |
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Cedric
Joined: 27 Aug 2004 Posts: 2600 Location: Sweden
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Posted: Thu Apr 22, 2021 3:50 pm Post subject: |
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But i didn't think the 911 pressure plate fit the s2, which one did you use? Do you have a pic on pplate? _________________ 1980 924 Turbo
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Carrera RSR
Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK
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Posted: Thu Apr 22, 2021 5:09 pm Post subject: |
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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 _________________ 1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Cedric
Joined: 27 Aug 2004 Posts: 2600 Location: Sweden
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Posted: Thu Apr 22, 2021 6:35 pm Post subject: |
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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. _________________ 1980 924 Turbo
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Carrera RSR
Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK
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Posted: Thu Apr 22, 2021 8:52 pm Post subject: |
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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. _________________ 1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Carrera RSR
Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK
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Posted: Thu Apr 22, 2021 8:59 pm Post subject: |
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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. _________________ 1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Dutch924-racer
Joined: 23 Jul 2007 Posts: 1076 Location: The Netherlands
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Posted: Fri Apr 23, 2021 2:42 am Post subject: |
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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. _________________ 937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller |
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Cedric
Joined: 27 Aug 2004 Posts: 2600 Location: Sweden
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Posted: Fri Apr 23, 2021 5:41 am Post subject: |
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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. _________________ 1980 924 Turbo
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peterld
Joined: 10 Dec 2006 Posts: 946 Location: Noosa Heads QLD Australia
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Posted: Sat Apr 24, 2021 8:38 pm Post subject: |
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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. _________________ 80/81 932/8 ROW |
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