Rubber center or cast iron clutch ?

robert walsh · 08-15-2008, 08:39 AM

I have seen pictures of the rubber centered clutch and the cast iron version and do not understand the advantage or disadvantage of either. I have a 1983 911SC 3.0, and have read of the rubber centered clutch being a problematic but i don't know the specifics of why, I drive the car for pleasure and do not track it at all, any suggestions on a clutck kit to use, they seem to be all over the board from $500 and way north, I just cannot contain a clutch chattering problem and am looking at replacing the clutch etc., could use a little guidance, would like to spend as little as possible but do want want to any way short change the end result, smoothness, response and performance. Will be paying for the labor as i am not qualified to do it myself. Open to all kit's out there just not the ones mentioned above. Have already replace all the mounts, clutch cable and helper spring and adjusted it correctly, it's about 80% better than it was but still drives me nuts when the chattering happens.

88911coupe · 08-15-2008, 08:46 AM

Rubber centered was designed to smooth out the shock of the clutch engaging. Nearly everyone replaces it with a "normal" type since the rubber can eventually start to disentegrate and cause problems. It's also considerably more expensive. I'm not sure when Porsche started using it so it may or may not be an option for your SC. Bottom line is I'm not aware of too many owners, if any, that have used the rubber centered clutch when replacing the old one.
Hopefully some of the many SC owners can chime in here.

KTL · 08-15-2008, 09:08 AM

The SC cars were the first ones known to have the "exploding" rubber-center clutch disc. They were later switched to the tried and true spring-center disc. Get a Sachs clutch kit for your car and you can't go wrong. That's not to say there's not other clutch kits that are also good but cheaper. Exedy, Dakin, Luk, Spec,...... the list goes on. You can shop around and get a lower price, but I don't think you can go wrong with Pelican's Sachs kit.

FYI, the rubber discs returned in the G50 cars in 1987 (and were still used in the Turbos long before this) and are more reliable but still prone to failing like the SC cars did. Just not nearly as frequently.

And if you've got a chattering problem, you may be wise to consider a new flywheel if your current one cannot be resurfaced. Some recommend not resurfacing the flywheel because it doesn't always turn out well and results in warpage.

robert walsh · 08-15-2008, 12:25 PM

My mechanic says he can resurface the flywheel, no need to replace, should i bite the bullet and spend the $300 for the new flywheel. He sys he's done dozen's of resurfacing of porsche flywheels without any problems. I think i'll buy the new one and be done with any possiblity of the clutch chatering anymore, does anyone else have any other items to look at when it's dropped and apart to eliminate the chatter problem, i want to fix anything that could be causing it.

teenerted1 · 08-15-2008, 12:33 PM

if it not part of the kit...throwout bearing, probably other parts too. just get all the regular stuff you need when doing a clutch replacment.

KTL · 08-15-2008, 01:20 PM

Throwout/release bearing is typically part of the kit- check Pelican catalog to be sure. One thing most people don't remember is the pilot bearing for the flywheel. I'd be sure to replace that since it's cheap and easy.

Only reason I mentioned the flywheel resurfacing is because others have had problems resurfacing these- John Walker comes to mind and i'm sure he's done more than his share of clutch replacements on these cars. I've resurfaced flywheels on the handful of clutch jobs i've done with no ill effects. But we're only talking about, like, 6 cars......

Could you describe the chattering condition a bit further? During clutch release? When pushing in the clutch? When applying a heavy amount of throttle from low RPMS? Need a bit more background to identify what you mean by chattering.

jmohn · jmohn's Garage

You may want to check for sufficient compression on the boudin (sp?) portion of the clutch cable housing. Insufficient compression (i.e. bow in the boudin) will cause some shudder when releasing the clutch.

JerryM
'78 SC

teenerted1 · 08-15-2008, 01:54 PM

Quote:

Originally Posted by KTL

Only reason I mentioned the flywheel resurfacing is because others have had problems resurfacing these- John Walker comes to mind and i'm sure he's done more than his share of clutch replacements on these cars. I've resurfaced flywheels on the handful of clutch jobs i've done with no ill effects. But we're only talking about, like, 6 cars......

i think JW has all these sent out now. at least he did when he did my tranny a few years ago. no issues after for me. YRMV

javadog · 08-15-2008, 02:22 PM

I've had three clutches put in cars in the last few years (2 in 930's and one in a Carrera 3.2.) I've gotten chatter when I didn't replace the flywheel. It may make a difference how the flywheel is ground and how bad the hot spots were before grinding. All I know is changing the flywheel fixed the problem, and I tried everything else (and I mean everything) without success.

JR

robert walsh · 08-15-2008, 04:01 PM

In reponse to Kevin, the chattering or vibration is evident in reverse and 1st gear particularly on an incline, it was very bad, my mechanic adjusted the clutch and replace the 4 mounts (eng/trans), he said the cable and helper seem fine, however i bought new ones yet to install, thought i would replace with the clutch and all the parts mentioned, perhaps i should the new cable and spring in first to see if it makes any difference? He felt it may be a pedal bushing issue so i bought new ones also. The clutck itsself has less than 20k on it, but when releasing in 1st or recerse i get a bad shudder sometimes, (on an incline it's much worse) but if you raise the rpm's and release it slower I can get it to take off okay, a quicker release can cause it to shudder then stall. I've had several british and german std cars, never had this problem. The adjustment he did a few months ago made way better but it is still there. If someone else dives it, it takes them a while not to stall it. Once in motion no problems at all, no grinding, slipage etc. I know this sound real stupid, but I just found the "new" cable and spring in the trunk, I asked him about it today and he said the ones in there are newer and fine shape, I had the valves adjusted 2 years ago and they swapped out the parts then.

KarlCarrera · 08-15-2008, 04:05 PM

FYI, the rubber discs returned in the G50 cars in 1987 (and were still used in the Turbos long before this) and are more reliable but still prone to failing like the SC cars did. Just not nearly as frequently.

The original rubber centered clutch on my 88 Targa was replaced at 49,000 miles with a 2nd rubber centered clutch by the original owner. I just had that one replaced with the Sachs kit at 119,000. the fly wheel was turned and re-installed. New t/o bearing. the car runs, shifts and drives excellent.

Just .02 from a 10 poster.

Karl
88 Targa

KTL · 08-19-2008, 11:12 AM

A bad clutch cable could easily cause the problems you have. But if it feels smooth and doesn't require much pedal effort, I doubt it's the cable. The cable guide tube is also a culprit for spotty clutch action.

To check the pedal bushings, disconnect the clutch cable and move the pedal back and forth. Does it feel smooth or is there noticeable resistance. There should be very little effort required to operate the pedal w/out the cable connected.

robert walsh · 08-19-2008, 01:07 PM

I have a brand new cabel and helper spring and a few new bushings planning on replacing this weekend. My mechanic said the spring and cable are fine, it was his thought that it may be a bushing problem at the pedal. The clutch when pushed in and out is not heavy or hard but it does have a weird point durring the release that it seems to have to go over a hump then continue and this is right where the chatter happen. I know it is a poor discription but thats what it feels like. I asked the mechanic if he could address the bushings but he said i would have to make another appt., every time it's 3 weeks out, few qualified in the saratoga n.y. area.

Superman · 08-19-2008, 01:41 PM

A special diamond stone must be used to grind these particular flywheels. The stone must have a SHARP outside corner, since our pressure plates fit INTO the flywheel. For this and other reasons, I would suggest you use a new flywheel. In fact, since you are having the work done, I would replace every clutch-related part including the guide tube and the fork. It is a few more bucks, but since you will be paying a handsome price for the labor, it doesn't make sense to gamble on parts. For your kind of driving, I would use Sachs and all OE stuff. Nothing fancy. Nothing aftermarket. And of course, I would make sure they replace the rear main seal and the transmission input seal. I cannot think of a clutch chatter problem I have seen that was NOT caused by a clutch disk contaminated with oil.

robert walsh · 08-19-2008, 02:31 PM

Thanks for the input, after this weekends intall of the new cable and spring, i'm quite sure i'll be dropping the engine and will follow your advice and replace everything, it would be my luck to spend the bucks and still have the problem, better safe than sorry. Thanks again

javadog · 08-19-2008, 05:16 PM

Quote:

Originally Posted by Superman

A special diamond stone must be used to grind these particular flywheels. The stone must have a SHARP outside corner, since our pressure plates fit INTO the flywheel. For this and other reasons, I would suggest you use a new flywheel. In fact, since you are having the work done, I would replace every clutch-related part including the guide tube and the fork. It is a few more bucks, but since you will be paying a handsome price for the labor, it doesn't make sense to gamble on parts. For your kind of driving, I would use Sachs and all OE stuff. Nothing fancy. Nothing aftermarket. And of course, I would make sure they replace the rear main seal and the transmission input seal. I cannot think of a clutch chatter problem I have seen that was NOT caused by a clutch disk contaminated with oil.

Amen to all those suggestions. One thing, though. I have just fixed a clutch chatter problem on one of my cars by changing the flywheel. When the clutch went in, the old flywheel didn't look all that bad, so it was resurfaced and reinstalled.

Robert,

When you get this done, shoot a picture of the face of the old flywheel and let us have a look at it.

JR

javadog · 08-19-2008, 05:19 PM

Quote:

Originally Posted by robert walsh

Thanks for the input, after this weekends intall of the new cable and spring

When you put the new cable in, lengthen it as much as possible at the clevis end (make sure you still have enough threads engaged.) Then do the basic clutch adjustment to set the preload and then measure and adjust the cable travel.

JR

robert walsh · 08-20-2008, 01:38 AM

I would like to get you guys photo's but I have to plan my life around the surgeon's appointment book, min 3-4 weeks out, followed by the time of day he schedules the surgery, and we all know these factors are similar to an aircraft actually departing on time. He's a very nice guy, quite knowledgable, when he's working on the car, smaller less entailed jobs he defers to the assistant, but there most be someone else in the Saratoga N.Y. area to work on the cars.
P.S. He is located in Ballston Spa N.Y. , When i puchased this porsche, '83 cab, it never even entered my mind that there is a true lack of skilled mechanics to work on them. Thanks again

javadog · 08-20-2008, 03:30 AM

Well, when you get the job done, ask the guy to give you the old parts. Then you can take them home and shoot photos at your leisure.

JR

glennspiegler · glennspiegler's Garage

When my 88 911 cab engine was out for a rebuild the orig rubber centered clutch was still in. I had read many articles about spring replacement clutches. Since I am a street driver, he insisted on rubber replacement stating that I would not like the vibration transmission that the rubber dampens out. 90,000 on the new clutch, alot of hwy miles with my daily commute. Any comments?