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Min clutch thickness?

Gang,

I have the motor out and disassembled...

I've been thinking about the clutch... I have the standard clutch with springs (not rubber centered) and would like to measure it for wear...

I don't want to replace it now unless necessary, since the trans will be coming out next year for freshening... What is an acceptable thickness on the clutch? How do I measure it?

Thanks,

Chris

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Old 10-22-2002, 06:47 AM
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Your clutch disc should have rivets in it. Check to see how much disc surface is left above the rivets. Obviously, the closer the surface gets to the tops of the rivets, the closer you come to losing your surface and totally screwing your flywheel up, not to mention the horrible sound it has to make (never heard it, but I can imagine it's bad). Maybe figure out how many miles you have on the disc and how many more you plan to drive until you have it out again. A clutch disc is something like $125. For that cheap insurance, I'd go ahead and replace it. If you have a real good digital camera, give us a closeup shot. My G50 rubber centered disc had PLENTY of life left in her at 82,700 miles. But was replacing the whole thing for different reasons.
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Old 10-22-2002, 06:55 AM
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The disc has about 2mm on either side... What is the stock new thickness on these things. The car has about 3000 track miles on it.
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2001 GT3 Cup - "Pepin"
1999 Spec Miata
1996 993 RS Replica
2010 Harley 48
2013 Honda 250 CRF
1971 Norton 750 Commando
Alcon Brake Kits
Old 10-22-2002, 10:07 AM
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Anyone have a new clutch that would be wiling to measure the thickness of the material from the rivets?

Thanks,

Chris
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2001 GT3 Cup - "Pepin"
1999 Spec Miata
1996 993 RS Replica
2010 Harley 48
2013 Honda 250 CRF
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Old 10-22-2002, 01:53 PM
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The clutch material BARELY pokes above the level of the rivets. If you can R&R the engine yourself, and if the material sits higher than the rivets, I would put it back in. But then, I'm trying to be the board's most notable cheapskate.
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Old 10-22-2002, 02:12 PM
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Chris,

Depending on the vintage of the clutch disk ... spec books show a min. thickness of 6.0 mm to 6.5 mm.

6.0 mm in '70 -'74

6.3 mm for '78 - '83

6.5 mm for 1969

No spec given for '84 thru '87 models!
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Old 10-22-2002, 02:33 PM
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Warren, is this total thickness, or thickness above the rivets?

My total thickness is about 7.75mm... ...and I'm wondering how this compares to new...In other words if new is 15mm and min is 6, then I'm pretty worn, but if new is 8.5-9 and I;m 7.75 then I'm in good shape...
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Last edited by cstreit; 10-22-2002 at 02:52 PM..
Old 10-22-2002, 02:48 PM
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Chris,

That is total thickness, and all of the 1970-1983 225 mm disks had a new spec of 8.1 mm +/- 0.3 mm. Probably the same for '84-'86 models, too ... just can't confirm it from the spec book.

The new disk in my Sachs Power Kit is 8.13 mm thick overall.
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Old 10-22-2002, 03:07 PM
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So it sounds like I could easily get another year outta this one. It's probably less than 25-40% worn...
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2001 GT3 Cup - "Pepin"
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2013 Honda 250 CRF
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Alcon Brake Kits
Old 10-22-2002, 03:36 PM
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That was my guess. I mean about being able to reuse it. I took my disk in to JW during my rebuild to ask him if he though I could reuse it. The friction material rises above the rivets, but not by much. He said with a sly grin "Only if you want it to last another couple of years."
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Old 10-22-2002, 04:58 PM
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Well if the original thickness is 8.13mm and minimum is 6.50mm and MY thickness is 7.75mm then than puts me at at only 23% wear... I have 4mm wear before I actually hit rivets...

Which is actually a lot considering there was only 5000k miles on the racecar. But clearly if I lost 25% in two years, I can keep the clutch in for another year or two without worries!

Thanks to all!

Chris
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Old 10-22-2002, 08:40 PM
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I just measured the thickness on my 88 3.2 and it's a shade over 9mm....sounds like I'm good for a while...correct?
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Old 12-06-2007, 10:31 AM
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Quote:
Originally Posted by Early_S_Man View Post
Chris,

Depending on the vintage of the clutch disk ... spec books show a min. thickness of 6.0 mm to 6.5 mm.

6.0 mm in '70 -'74

6.3 mm for '78 - '83

6.5 mm for 1969

No spec given for '84 thru '87 models!
74-78 spec?
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Old 08-02-2020, 07:05 PM
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I had my engine dropped to do my throw-out bearing last year. I measured my clutch against the spec and was at 22% left. It took 70K miles (daily driver) to burn the top 78%, so I figured it was going to make it to about 100K miles total before needing replacement. That is maybe 2-3 years with my normal mileage.

I have 3 kids now, and finding the 2 weekends to drop and then lift the engine is getting difficult. I went ahead and did the replacement, and now it should last until the kids are old enough to help!
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Old 08-03-2020, 06:26 AM
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So I just measured my friction disc from my 77. It's 7.5mm. So.... kind of a waste to change it, no?
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Old 08-03-2020, 10:58 AM
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I guess I am not that much of a cheap skate. The Porsche Clutch Disc (225 mm) - Sachs 1878005583 is just $181.50.

Nothing to to just ignore, but the labor to R&R an engine and clutch it just seems like a no brainer. Replace it if it has more that minimal wear. But that is just me.
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Old 08-03-2020, 12:05 PM
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Wayne's book How to Rebuild & Modify Porsche 911 Engines 1965-1989 has a list for the Clutch Tolerances in Appendix A for all of the engines up to 1989 except for the 89 930.

911 (1975-1986)
New thickness 8.1 +/- 0.3
Wear Limit (symmetrical) 6.3

Wayne's data for the 1987-89 G50 data is different than the workshop manual. I don't have access to the spec book so maybe it is listed without compression there.

Wayne's 911 (1987-1989)
New Thickness 10.1 +/- 0.3
Wear Limit (symmetrical) 8.5
Lateral Runout 0.5 max

The workshop manual 87 Models Onward
New 9.3 +/- 0.3 mm compressed
Wear limit of 7.5 mm compressed
The figure for compression shows the disc being compressed with a hand vise.
Lateral runout 0.6 mm measured 2-3 mm from circumference.

Last edited by HaroldMHedge; 08-03-2020 at 04:41 PM.. Reason: Add 87 Models Onward Lateral Runout
Old 08-03-2020, 04:33 PM
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Is there any way to get an idea on your clutch wear w/o dropping the motor? I mean, on my '84 915...if I messed with the clutch cable adjustment, is a some way to translate the position of the adjustment to how worn the clutch is?
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Old 08-03-2020, 07:35 PM
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Quote:
Originally Posted by JohnTucker View Post
Is there any way to get an idea on your clutch wear w/o dropping the motor? I mean, on my '84 915...if I messed with the clutch cable adjustment, is a some way to translate the position of the adjustment to how worn the clutch is?

If you're running out of room on the cable the disc is probably worn.

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Old 08-03-2020, 07:37 PM
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