s54venture

I have an 82 Competition 5 speed.
So I recently came across a woman selling 928 parts on CL and I went and bought them all.

Among the parts was a mostly complete clutch.
Pictured is what I got, in the order I think they go in the orientation I think they go.





Recently my clutch has refused to release, it seems like a collapsed pressure plate to me, I've read about some self adjusting shims that might need resetting, but I haven't looked too hard into that.
I don't really think it's the little shims I read about, mainly because the new clutchfork has no play with the throwout and pressure plate, while the one on the car, when it fell off the little ball up top had all sorts of movement.

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My car only has ~60k miles on it, but more likely than not I'm going to take out the existing and replace the clutches and bearings.
Pelican shows that the front and rear clutches are different parts, and one of the two is NLA from sachs and porsche.
928MS was going to be my next option, I don't plan on adding any power to this car so stock would have been fine.
The clutches I've got seem fairly new, but they seem identical, so how can I tell which is front and which is rear? Or are they both the same and I'm missing one side?




They also look used, so I compared the material to a quarter, are they any good anyway?



I don't see any branding on them either, but the flywheel side sticker probably gives the brand away.
I'd hate to waste a still good part, but 928MS sells the clutches for only ~$600 so would I be best off just buying brand new ones?

That just about does it, i always pack a million questions into threads when I make them, any input is always appreciated.

SeanR

Those disks are not factory 928 parts.


Check with Roger@928srus.com for factory disks.

Dave928S

^^ What Sean said .... and the pressure plate may not be factory either.

Once you have all the correct parts that will play together, you'll need to make sure that they're assembled correctly, which will include balance.

There have been a few recent threads on clutch components and adjustment that would be worth checking, to fill you in on all the differences.

s54venture

The pressure plate is sachs. I'll go hunting for the clutch threads.


Thanks, I sent an email, it's probably just best to get new ones, I don't want to be messing with the clutch all the time.

Dave928S

It might have the Sachs casting marks, but it's likely to be re-manufactured.

The pressure plate blue paint is typical of aftermarket PP's with increased clamping force, such as the ones you'll see on 928MS site, which have the same blue paint and puck style friction disks, like yours.

You need to determine exactly what you have with each component, so that you can be sure you're going to end up with a pack which works as it should.

Genuine new Sachs out of the box are not painted ...

s54venture

I didn't think about that, after googling around it seems like the clutch discs are the Spec stage 2 discs. SP802
They look just like the stage 2, not their 1 or 3. And the FW side decal looks identical.
Spec also seems to paint their pressure plates blue.

Considering I'm now planning on buying new OE clutches from 928rus, and new pressure plates are $300 I guess I should just skip using any of it really.

Dave928S

I guess that's a decision only you can make .... but ....

I've stuck with the known quantity of OE, as when correctly installed and adjusted it works fine.

It may be that the Spec components are still OK, but who can tell if you'll get a correctly working assembly. I personally can't see that the friction face area of those disks is a good design, as I think they could cause hot spotting (you can already see glazing around the rims).

If the Spec parts seem OK maybe you Ebay them to partially fund your OE parts.

s54venture

Something so easy to see in person, so hard to show on camera.







There is plenty of evidence of hot spotting already.

I do like having cars closer factory than further. There's always a few things per car that really could use improvement, but for the most part I like OE too.

Not being able to use these parts wouldn't have changed my mind on buying these 928 parts anyway, I kind of got a screaming deal for a 16v motor, a manual open dif trans and an auto open dif trans and boxes and boxes of other bits.

ROG100

One clutch plate is still available OEM and both are still available from Porsche but more expensive.
We stock them both.

The expensive part is the intermediate plate - it may be reusable after a light surface skim - however let the experts advise on this.

One of the MOST important parts is the correct high pressure grease for the splines - do not use anything else!!!! Yes we stock that as well.

Disc 1 = $205
Disc 2 = $336
Pressure plate = $318
Intermediate Plate = $840
TO Bearing = $150
Pilot Bearing = $6.50
Guide Tube = $75
Release Arm Bush = $14.75
High Pressure Grease = $22.68

Lizard928

The problem is not the discs.

I got a set of those discs with the PP from the seattle group because they couldn't get them to work.
The problem is the PP.
Use your original PP and the problem will disappear.

Dave928S

I think it's quite probable that the Spec PP is a significant part of the problem, as Colin has experienced ... but that doesn't mean that all the items Roger listed don't need to be spot on as well, to get the whole pack working as it should.

I have no doubt that the friction discs will work ... to a degree ... but they cannot work as well as a standard disc, as they don't have the same friction material surface area each side, and the wear pattern is grossly unbalanced.

I've calculated the surface area of the friction material on one side of a standard clutch disc as approx 169 square centimeters, which is the annular ring area less rivet hole area.

The area of friction material on one side of the Spec disc, is approx 103 square centimeters, which is the annular ring area less the eight tab cutouts.

The friction material area of the Spec discs is 61% of the friction area of the standard disc. Expecting that diminished area of material to perform the same job, would be akin to expecting brake pads of 61% of standard pad area to do the same work.

Note: The Spec lining material is listed as Kevlar, which has a coefficient of friction of about 0.36, with standard brake and clutch materials having a coefficient of friction of around the same value. For the smaller friction surface area Spec discs to work they obviously requires a higher clamping force PP to achieve the same or greater performance ... with the standard PP they will perform at much less a value than the standard discs.

The difference in area is obvious in the comparison photos below, as is the totally unbalanced wear pattern on the Spec disc, compared to that of a used standard disc.

I would want to see some compelling technical data, and stats of history of successful use, to be using other than standard clutch components for street use.

Lizard928

Dave,

The reduced surface area of the friction discs, will actually work without any issues, and will hold more force.
The reason has to do with not only the compound, but the reduced surface area.
A reduction in surface area results in a greater amount of pressure on the surface area in contact.

example, a truck on regular tires will sink in to the snow because of a very small contact patch with high surface pressure, where as a tracked vehicle will stay suspended on the surface of the snow because it's much larger contact patch has a very low surface pressure.

Will it last as long? Unlikely, but clutch life is not an issue in a 928.

Carl Fausett

Don't throw that intermediate plate out - I can use it for a core.

I'll pay $40 cash or give a $55 in-store credit for it. It just has to be all-there, and have a good ring gear on it. The friction surface can be scared and warped - no problem. I pay for shipping but the shipping has to be postal - cheapest way.

Contact me BEFORE you send yours in.

I'm also looking for bad early throw-out bearings to use as cores to rebuild and provide an advance-exchange for my customers.

Lizard928

Better idea,
I can just fix it for you.
Or tell you how to fix it.

The problem is there are no stops (like factory clutches) so the pull back springs get over extended. You can use pieces off the factory PP to fix this one and make it work.

mark kibort

not the best analogy.. if there was one little one square inch point of contact, the psi would be 400lbs per square inch on that surface contact point , or 400lbs of force. if the discs had more contact area.. say 12x, the force still on the overall disc is 400lbs , just less for each 1" square area. (less chance of scoring and wearing odly) the analogy only works for why a nail can penetrate wood, and not the hammer.

as you said, there is NO problem with the stock stuff. ive heard all sorts of horror stories, but the ONLY thing i have seen going up from 240ftlbs to 420ftlbs of torque out of an engine, is the pressure plate can be weak and slip... upgrading the pressure plate is a way to fix that problem. wear is NOT an issue. and the stock clutch is good up to 350ft-lbs of engine torque NO problem. (and most of all, no wear issues or grip issues)