924Board.org

bass gt · Posted: Wed Apr 04, 2007 4:17 am Post subject: Clutch, clutch, clutch

Gents,

Hoping to tap into some of the collective wisdom here. I have a strange query you may be able to help me with.
OK, my car is a Series 2 931, and had the stock clutch assembly fitted, except the new friction plate i fitted last year.
I then purchased a 911 Sachs sport clutch pressure plate, as would you believe it, it wont fit.
The problem is this. The stock pressure plate is a lot deeper than the 911 type, with the friction disc protruding beyond the mounting face. Now when i offer up the 911 pressure plate, the friction disc is inside the assembly, by about 3-4mm. So when i fit this to my flywheel, there is a 15-18mm gap between the two friction surfaces. Obviously WAY too big.
Now, i have a load of old bits floating about, and guess what, the deeper pressure plate fits the clutch disc with the big rubber doughnut mounted spline. When this is offered up, hey presto, all the faces mate up.
So, am i right in assuming that the S1 and S2 flywheels are different in terms of their friction disc mating surface height??
And do i ned an S1 flywheel to make this work. Or, can i use a Fidanza 924 NA flywheel, as i am now longer using the ring tone as my ignition trigger?
Sorry for the long post, but any insight or info anybody has would be of great help.
Best Regards,

Steve

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Hey Steve,
Is the friction surface of your flywheel on the same plane as the surface where the pressure plate mounts against? I think that may be the trouble. The flywheel should be flat across the friction and mounting surface (where the bolt holes are), and have a little lip around the outside that the entire plate fits within.

I'm not sure what the story is with the rubber-center disk. As long as the thickness of the friction material is the same, a rubber or spring center disk would fit identically.

We need pics

For reference, here are the 931 S1 parts -

_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

bass gt · Posted: Wed Apr 04, 2007 5:41 am Post subject:

Nick,

No, my flywheel is deeply dished!! The PP sits down into the flywheel, as does he frictions plate. Once i get home, I'll upload the pics and post them up
Steve

bass gt · Posted: Wed Apr 04, 2007 8:32 am Post subject:

Guy's,

You can clearly see how dished the flywheel is. It has had a tiny skim, about a couple of thou, to clean it up, but thats it, thats how it came from the car. And as for the 2 PP's, the silver is the 911 unit, and the old is the one from my car.
Oh, and check out the crank and rods

Steve

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Need bigger pics - my eyes aren't that good!

* edit, ok I see the pics now!

It looks like there is a huge difference between the friction surface on the flywheel and the mounting surface for the pressure plate. Mine is flat, and 911 flywheels are also flat between the two surfaces. Yours doesn't look stock by any means to me! What does it weigh in at?

Also, where did you get the pressure plate you had before that worked with it? You were right, the friction surface on it protrudes by a lot! That doesn't look like any of the stock 931 plates that I've seen.

Everything I have has the same part numbers listed for S1 and S2 clutch packs. This is a real head-scratcher!
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

bass gt · Posted: Wed Apr 04, 2007 10:41 am Post subject:

Nick,

Weird Eh?? Well that flywheel weighs very little, however, that is offset by the weight of the iron PP!! But that is going to be lightened as well.
Just checked my other engine, and guess what, it has a flywheel much like yours. Weighed that and the 911 PP and there is a total weight saving of 7kg(15.5lb) over the stock items.
I think i will try the stock looking items in this engine, and the ali flywheel/PP in my other. Might be interesting to see how the spool ups compare, given they will share the same head and turbo.
I have somebody over here looking a their S2 clutch this week, to see if this is how the UK/ROW S2 clutches are.Very strange that Porsche would fit different flywheels todifferent markets. However, with the US cars running less boost, and generally being detuned a little from the factory, maybe this is part of the deal.
I'll keep you posted if anything turns up.

Steve

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

Pressure plate? What pressure plate??

_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Smoothie · Posted: Wed Apr 04, 2007 2:34 pm Post subject:

Yes, nice looking workbench.

I got a look at the "E_924_85_KATALOG" .pdf (Euro PET .pdf).
It does show a couple more pressure plates than the USA PET.
They are
931.116.001.02 for M31.01/02, M31.03/04 -also used on US cars. -and only with the spring damped clutch plate 931.116.011.04

915.116.001.27 for '81 M31.50 -only with the spring damped clutch plate 931.116.011.04

931.116.001.03 for '81-up M31.03 -only with the rubber damped clutch plate 944.116.012.08

Maybe see if you can find that 915.116.001.27 number on the unusual pp.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Wed Apr 04, 2007 2:48 pm Post subject:

For flywheels... they show 931.102.206.01 for use with engine types M31.50/03

engine types from the tech specs booklet -
M31.01 is Euro 79-80 931 ....... clutch contact force = 7200-7900N
M31.02 is US/Can 79-80 931 .. clutch contact force = 7200-7900N
M31.03 is Euro 81-84 931 ....... clutch contact force = 7200-7900N
M31.04 is US/Can 81-82 931 .. clutch contact force = 7200-7900N
M31.50 is "924 Carrera GT" .... clutch contact force = 7800-8500N

The guess from this is that you have some Carrera GT clutch parts.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

[img]http://i115.photobucket.com/albums/n281/daverea/daverea3251.jpg?t=1175727282[/img] [/img]http://i115.photobucket.com/albums/n281/daverea/daverea3252.jpg?t=1175727178[img][/url]

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

finally, with the help of my wife lol, some pics of the two different style 931 flywheels (both S2's).

bass gt · Posted: Thu Apr 05, 2007 9:21 am Post subject:

Interesting!!!
Mine is the same as the dished type. I'm guessing these are used for the rubber friction discs, which were introduced later on.
Is there a weight difference between the 2???

Steve

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

according to my digital bathroom scales they both weigh in at 4.9kg. so its safe to say they weigh the same if not precisely 4.9kg.

i used my rubber centred plate/pressure plate on a 944 engine so i cant do a weight comparrison with the spring centred plate/pressure plate.

BTW, flywheel for use with rubber centre plate .... 931 102 206 01.
flywheel for use with spring centre plate .... 931 102 206 03.

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Wild. I didn't know that any 931's came with a rubber centered clutch.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet