Bulvot

I finished the installation of a Spec Stage 2 clutch (model SP142) on my 1987 928 S4 today. It's supposedly rated for 525 ft lbs of torque. I've only put 20 miles on it with a couple of dozen starts from a stop and several dozen shifts at speed. But, these are my observations so far:

• The very first three or four times that I engaged the clutch, it shuddered a little bit. Nothing that wasn't manageable with careful feathering of the clutch and throttle, but it was there. After that, it hasn't shuddered at all, not even a little.
• The pedal travel from fully released to fully engaged is about half the distance that it was before. That is probably a combination of my old clutch being completely worn out, and the new clutch being rated for more torque.
• Engagement is positive and smooth, albeit quick.
• The pressure plate and clutch disc looked to be well made, and the disc was properly marked which side faces the flywheel.
• Installing the pressure plate was a tighter fit than the OEM one coming out. The centering pins just barely cleared the flywheel with a little bit of dragging. Not enough to gouge anything, but it was a tight fit. I used a bridge jack on my lift to slowly and precisely raise the pressure plate into position. I can't imagine doing it by hand while laying on my back. It would be doable, but not for someone who's not in good shape. It took more effort than the OEM would have (in my opinion).
• The release arm bearing that they supply with the clutch is made by SACHS. They do not provide the pilot bearing.

I haven't really stressed it yet, but it is definitely holding in situations where my old one was slipping. So far, I am very happy with it.

After I've got at least 1,000 miles on it and have really hammered it, I'll report back.

Bulvot

I paid $818 for the kit (pressure plate, clutch disc, release bearing) on sale at Pelican Parts, but it is now $939. This is the kit on Pelican Parts' web site: https://www.pelicanparts.com/More_In...42&SVSVSI=1002

You can order it from just about anywhere, even non Porsche vendors. It is drop shipped from the manufacturer.

This is the manufacturer's site for the single disc clutch options for the 928: http://specclutch.com/cars/Porsche/928/1987/Single

And here is a breakdown of each available stage: http://specclutch.com/products

Petza914

Glad you're happy with yours.

I hated it in my 928 from a grabiness and shuddering perspective, with no ability to normally engage it without the whole driveline shuddering. When I put my 928 back together from the engine R&R currently underway, I'm reinstalling it with the OEM friction discs that have the marsailles spring between them (the SPEC discs do not), the lightweight Aasco flywheel, the OEM intermediate plate, and the Spec pressure plate, and hoping that combination works much better for me. If not, I might try an OEM flywheel with the SPEC discs to see how that works.

Looking at the spec friction discs I removed, they look like they have virtually no wear and are still even on both sides of both discs. I think the material is just too hard for smooth engagement. It's also possible that I was having some issues with my slave cylinder (replacing that while I'm at it), so we'll see, but looking forward to a better future clutch experience. If all goes as planned, I'll likely sell these spec friction discs to someone that wants the higher friction bite they offer or keep them as spares in case I want to try them again with the other changes I've made to the clutch setup.

Bulvot

I don't think that we're talking about the same product. Yours appears to be a Stage 3+, correct? That's significantly different material and rating than the Stage 2 that I've referenced above.

I didn't take a photo specifically of the disc, but the below image taken from the corner of another photos shows that my disc's material is very different from yours:

Petza914

You're very right about that. Mine was supposed to be just a light upgrade, but looking at the metallic content of my friction disc vs yours, I think I know why mine was much grabbier and why I don't like it. You'rs looks a lot more like the OEM material, just in a segmented type pattern. I didn't select the clutch that was in my car, which is why I'm unclear what it is. If SPEC has their info booth at the Mitty races at Road Atlanta this weekend, where I'll be on Saturday, I'll show them the pictures and let them tell me what I have, then add that info here to contribute to the knowledge base.

You also have a sprung hub and single disc clutch vs my dual disc with intermediate plate and unsrung hub, so that's another major difference. The springs in the hub help with engagement smoothness.

Bulvot

Even worse, I just noticed that yours has a solid hub! Yikes, that is most likely a Stage 5 disc!! From their site:

Types of Driving:

Street, Drag, Pulling, Autocross

Features a full-metallic disc with the highest possible friction co-efficient. Street drivable but not street-friendly. The hub is solid 12-rivet and the assembly is heat treated for strength and durability. Best for extreme street and drag racing.

• High clamp pressure plate
• Full-metallic friction material
• High torque solid hub and disc assembly
• Bearing and tool kit

Spec doesn't even list dual disc kits, so I'm guessing that you bought it through 928 Motorsports. You might want to talk to Spec directly and confirm dimensions (thickness) on their discs and see if you can go with a smoother operating setup that still provides greater strength than stock. When I selected mine, I specifically looked for the non-puck style disc that did not have semi-metallic facing on either side. But even one face with kevlar and one with semi-metallic would be much better than what you've been using (both sides semi-metallic). It didn't even occur to me to consider a solid hub. That's nuts.

I think that this is exactly why a lot of people say that Spec clutches shudder, aren't suitable for the street, etc. They order a clutch purely based on what torque it is rated for, and of course they operate off of the "more is better" mentality, and don't consider the facing material. Most people are probably ending up with semi-metallic or full metallic disc.

I would love to have more holding power to accommodate my upcoming forced induction project, but I'm very happy with how smooth the Stage 2 disc is.

Petza914

I'm hoping with the stock friction discs I'm going to that it will smooth things out - heck, anything in the right direction will be an improvement. Though I'm supercharged at around 375-400 HP at the crank, moving to this style of dual disc clutch with the intermediate plate should give me enough holding power compared to the early single disc clutch my '79 had originally (though that was before the supercharger). We'll know in about a month when I have a motor back into the car and everything reinstalled.

Bulvot

Anything would operate smoother than what amounts to the solid steel discs that you had installed before

Bigfoot928

I have the stage 3 discs and the breakin was difficult. They say it takes 500 miles of stop and go traffic, and I was at the point I was ready to rip it all out and start over again. I have several sets of the dual disk clutches as a standby.

Petza914

I had 15,000 - 20,000 on mine before pulling the motor this month.

Still waiting for that break in... LOL

Bulvot

There is a huge different between Stage 2, 3 and 5.

ptuomov

Stage 3+ is not nice to drive. I hate it.

But on the plus side, it does not slip.

Bigfoot928

I had 4-5K miles on mine but they were all highway miles. I started driving it around town, just to break it in, and it sucked. but it finally got just clicked one day and was good to go.

Bulvot

I've now got about 1,700 miles on the clutch, including 1,300 round trip to Atlanta and back. It is outstanding. Zero shuddering, no slipping, consistent engagement. I'm very happy with it.

Chris Lockhart

Good to hear!. Thanks for the report.