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Clutch Disc Options
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peterld  



Joined: 10 Dec 2006
Posts: 771
Location: Noosa Heads QLD Australia

PostPosted: Mon Apr 05, 2010 12:02 am    Post subject: Reply with quote

Well I think I've answered my own question. Based on what was available locally (ie. ROW RHD) I was under the mistaken belief that all S2 DITC cars had the rubber damped clutch. Dan's reply got me thinking and searching. I've located a USA S2 flywheel (non rubber damped) and what a difference to the ROW rubber damped version! Unfortunately I don't have a corresponding clutch and pressure plate, however I do have a S1 clutch and pressure plate at hand and it would seem that they will mate up nicely with the early version S2 USA flywheel. All bits are filthy and rusty so I can't tell definitively until they are cleaned up and properly measured.
So what's the point of all this - run DITC without having to use rubber centered clutch! and thus eliminate the weakest point in the drivetrain.

So for what it's worth - there are at least FOUR versions of 931/932 flywheel available (forget the PET). ROW S1/USA S1/early S2 USA/ ROW S2 and late S2 USA. The major difference is that the rear (closest to crankshaft) on the earlier flywheels is largely flat while the rubber centred version (late S2 USA and S2 ROW) is dished.
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Mon Apr 05, 2010 2:55 am    Post subject: Reply with quote

It will be interesting to see what version is in the 81 euro I just bought. It was manufactured in Jan 1981
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gegge  



Joined: 27 Jul 2007
Posts: 1075
Location: Sweden

PostPosted: Mon Apr 05, 2010 5:43 pm    Post subject: Reply with quote

I think there are at least one more flywheel and there could be two versions of the flat S2 flywheel: Carrera GT and US

I have been searching for a flat S2 flywheel just like the US version for my ROW rubber project. But all US got a "USA" casted on the surface due to different ignition timing on the trigger wheel compared to ROW. I havn┤t seen this with my own eyes, but Porsche tech manuals are showing this. I don┤t know the PET number for this one.

I do have two flat S2 flywheels with PET numbers that are correct for Carrera GT. ( And one mysterious billet S2 with nothing on)

Then you have the GTS/GTR flywheel, but I don┤t know if the ignition was triggered by the flywheel: 931.102.207.00
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K-Roll931  



Joined: 08 Jul 2017
Posts: 64
Location: Southfield, MI

PostPosted: Fri Feb 21, 2020 11:34 am    Post subject: Reply with quote

I've been trying to figure this out for weeks.....Can I or can I not use a spring centered NA 944/924S clutch kit or even disc on an 1980 S1 car (09/1979 build date)??
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ideola  



Joined: 01 Oct 2004
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PostPosted: Fri Feb 21, 2020 12:10 pm    Post subject: Reply with quote

No. 931 or 86 Bronco II
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K-Roll931  



Joined: 08 Jul 2017
Posts: 64
Location: Southfield, MI

PostPosted: Fri Feb 21, 2020 12:23 pm    Post subject: Reply with quote

ideola wrote:
No. 931 or 86 Bronco II


Well, I guess I'm getting a pressure plate, throwout bearing, and Bronco II disc.

Thanks Dan!
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Fri Feb 21, 2020 11:04 pm    Post subject: Reply with quote

Dan!!!!

Long time no see!

Hey, can you elaborate on the differences? Is it just for the snailshell cars, then?

I would swear I put a 944 clutch kit in my '82 US 931, but it was a while ago, could have been a 931 part I bought?
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Fri Feb 21, 2020 11:43 pm    Post subject: Reply with quote

It's not specific to the trans. The really late 82 931 in US had the 944 rubber damped setup. All other 931 up through midyear 82 had the spring damped setup. I suspect PET may provide a VIN break point, but I haven't checked.

The late S2 flywheel on the rubber damped setup is unique to those cars and is much deeper than those with spring damped. As a consequence, on the pressure plate for the rubber damped setup, the friction surface that clamps the disc against the flywheel sits proud of the housing, while on the earlier setup (both S1 and S2), the friction surface is slightly recessed.

The S1 cars can use first gen S2 flywheels, which saves weight, but S2 cars can't use S1 flywheels unless you ditch the DITC (pardon the pun) due to the sintered insert required by the S2 crank pickup.

All 931 with spring damped clutch disc can use any of the 915 pressure plates. There are 3 variants of 915 pressure plate housings: all cast iron; part iron, part alu; and all alu. The alu variants obviously save weight, and aid in quicker acceleration. The 915 part numbers also provide 50% more clamping force than the 931 PP, and are therefore desirable upgrades on 931s with increased BHP as they resist slippage more than the OEM 931 part number pressure plate.

It is conceivable that one could find a late S2 flywheel and use a 944.1 rubber damped setup. BUT WHY? No advantage wrt clamping force, and the rubber dampers are notorious for disintegrating. The failure mode on the spring damped discs is loss of friction surface, not a giant exploding rubber donut. So you be the judge 😉

The ideal setup, IMHO, is a 915 hybrid iron/alu PP, OEM 931 throw-out bearing, gen 1 S2 flywheel, and the HD (heavy duty) Bronco II clutch disc with 6 (rather than 4) springs. The all alu PP is virtually impossible to find. Neither of the alu versions are available new, at least as far as I'm aware, so you have to scour Pelican 911 postings to try to snag the iron/alu unit used. Expect to pay 911 prices. But worth it.

It's also worth noting the S1 flywheel can benefit from significant weight savings by lathing out LOTS of material. I've been able to shave ~40% off of S1 flywheels. You can shave maybe 10% off of S2 flywheels. Some of the S2s I've pulled from cars were drilled and balanced at the factory! It's highly beneficial to "internally balance" the flywheel and pressure plate, i.e. spin them individually and balance them by selectively removing small amounts of material by drilling out divots on the "heavy" side. Sort of the inverse of adding wheel weights when balancing tires. Then double check balance of the entire assembled clutch pack and fine tune. Helps with a smoother running engine, especially high-performance builds. Rule of thumb, if it rotates, balance it (crank, cam, sprockets, pulleys, pressure plate, flywheel); if it reciprocates (rod, piston, lifter), weight match it to its counterparts.

I have other posts here with part numbers. I'm phone posting, so you'll have to search those out on your own, just use "ideola" in the author field, and "915 pressure plate" + "all words" in the search terms.
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CÚdric  



Joined: 27 Aug 2004
Posts: 1973
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PostPosted: Sat Feb 22, 2020 12:42 am    Post subject: Reply with quote

Be careful here to call the "s2 and 944" clutch plate rubber centered, because they have been spring centered for many years. So people dont get confused.
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Sat Feb 22, 2020 12:49 am    Post subject: Reply with quote

944.1 (1982-1985) came with rubber damped clutch disc and so did the very late 82 models, at least here in the US. 944.2 (1985.5-onward, including 924S) went back to spring-damped.
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Sat Feb 22, 2020 1:02 am    Post subject: Reply with quote

Here is an example of what I'm talking about, although this is incorrectly listed as for the 924S.
https://www.ebay.com/itm/OEM-SACHS-Rubber-Center-Clutch-Disc-225mm-for-PORSCHE-924S-early-944-2-5L-N-A/124071075466

PET does not illuminate, it only lists one part number, so I believe what happened is they deprecated the rubber center clutch discs because they failed, probably due in part to leaky rear main seals getting oil on the rubber. But I can assure you based on my own experience of parting out multiple late model run 931 S2s as well as early 944s that they came with these rubber donut clutch discs.

I spent many hours investigating whether there was an upgrade path from 931 parts to cheaper more plentiful 944 parts, but the differences in the flywheel (depth and bolt pattern) were the show stopper.
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924RACR  



Joined: 29 Jul 2001
Posts: 8293
Location: Royal Oak, MI, USA

PostPosted: Sat Feb 22, 2020 1:08 am    Post subject: Reply with quote

Thanks for the detailed reply!

Never thought about getting the flywheel balanced, just turned or lightened... but it's a damn good idea, makes sense!
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CÚdric  



Joined: 27 Aug 2004
Posts: 1973
Location: Sweden

PostPosted: Sat Feb 22, 2020 1:36 am    Post subject: Reply with quote

Yes your right bout them coming with rubber centers from the factory, i was talking about the later replacement kits. Where SACHS replaced the rubber centered part number with a spring centered one, probably because of the issues you mentioned. My s2 engine for example had the spring clutch in it when i bought it, replaced some time in other words. I dont know exactly which year SACHS swapped out the rubber one though.

I got my flywheel with pressure plate balanced last time i did the clutch, not that expensive while your there
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K-Roll931  



Joined: 08 Jul 2017
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Location: Southfield, MI

PostPosted: Mon Feb 24, 2020 7:42 am    Post subject: Reply with quote



Here's a picture of the Bronco clutch next to my around 53,000 mile original clutch.
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