Driving without rubber on 78SC clutch

[RazorRacer]

The best I can tell, my rubber is gone from the clutch on my 78SC. It has 90K miles on it. I can avoid the lurching be carefully shifting. Do you see a problem to continue doing this? How will the clutch eventually break? It's been like this for 20K+ miles.

[chrisp]

You need a new one so you might as well put it in and enjoy the new clutch while you still have the car. Any future PPI is going to catch this and will want $750+ credit to fix it.

To answer your question. I would never drive it like that because you have taken the shock absorption out of the system. Now it's metal on metal and it shock loads the system which isn't good. You're beating up your tranny. Who knows maybe you'll even start shearing flywheel bolts if it hits hard enough, many, many times over.

[bigchillcar]

razorracer,
i'm wondering if i don't have the same problem. i need to go back in my records and see when the clutch job was last done and try to tell if i have the rubber centered or spring version.

anyway, it feels like i have a significant amount of what i call 'preload'...if i just tap the gas pedal, it clunks...kinda like what i remember about old, worn out u-joints. does yours do this? once it's loaded, it doesn't slip...just annoying as i initially tap the gas when it's in any gear.
ryan

[banjomike]

Lucky you. When this happened in my 944 a chunck of the rubber got into the clutch making it impossible to disengage. I would think that the lack of damping would cause pretty significant 'impulses' of force in the various parts of the drive train including the tranny, the motor, the CVs, etc.

It's a Porsche, it deserves to be maintained like one.

[89turbocabmike]

You really need to address this. I blew my rubber-centered disc and drove it carefully for about a week before tear-down. Once the rubber is gone the force is transmitted metal to metal and has about an inch of play from side to side. It looks like it could go some time like this driven carefully but beside the obvious possible damage to the rest of your drive-train, when it goes(and it will) you'll likely spend a considerable amount of money(tow) and time(inconvenient) that could have gone to a new clutch. Besides, how much fun is it to drive like that

[Mike Kast]

Originally posted by banjomike
Lucky you. When this happened in my 944 a chunck of the rubber got into the clutch making it impossible to disengage.

When I read about this problem with the rubber centered clutch that is what the book said generally happens. The rubber jams you out.

[RazorRacer]

Originally posted by 89turbocabmike
You really need to address this. I blew my rubber-centered disc and drove it carefully for about a week before tear-down. Once the rubber is gone the force is transmitted metal to metal and has about an inch of play from side to side. It looks like it could go some time like this driven carefully but beside the obvious possible damage to the rest of your drive-train, when it goes(and it will) you'll likely spend a considerable amount of money(tow) and time(inconvenient) that could have gone to a new clutch. Besides, how much fun is it to drive like that

My 78SC lurches back and forth at low rpm in 1st and 2nd gear. The slack is in the clutch. It's been doing this since I got it at 64K miles and now it has 90K miles. Since your's lasted only a week, my car must have a different problem.

[toolman]

No, it is the same problem, don't try to cheap it either. Get the whole kit and put it in some weekend. You might even find something else wrong upon disassembly.

[chrisp]

..... or the damage being done hasn't created a catostrophic failure......yet.

It may be a time bomb ticking.

Perhaps it has a spring center clutch and maybe only one or two of the four springs are bad and although you feel it shuddering it is not as damaging as when the rubber center fails.

[chrisp]

or do what I did and pull the motor for a clutch and put it back in 3 months and $7500 later.

It started as a clutch replacement/SSI/muffler upgrade ($1500) and a "while I am in there project" ($1000). Then I found a broken cylinder head stud and decided to do a rebuild ($5000).

Although most of it was unbudgeted I was happy that I caught the head stud before it trashed anything else and led to even thousands more in damage.

[350HP930]

I drove mine with bad rubber disk for over 20K miles.

Learning to shift a 930 tranny gracefully enough to not feel the slack did allow me to fine hone my clutching skills.

In the end the metal turn stop that keeps it from spinning eventually gave out, but that was after a lot of exposure to almost 400 ft-lbs of torque.

It wasn't catastropic since it did no damage to anything else.

[RazorRacer]

Originally posted by 350HP930
I drove mine with bad rubber disk for over 20K miles.

Learning to shift a 930 tranny gracefully enough to not feel the slack did allow me to fine hone my clutching skills.

In the end the metal turn stop that keeps it from spinning eventually gave out, but that was after a lot of exposure to almost 400 ft-lbs of torque.

It wasn't catastropic since it did no damage to anything else.

That's what I am thinking. When it fails, it fails. It's not hurting anything to continue driving like this.

[chrisp]

Sounds catostrophic since that metal piece failed.

What hidden damage has happened inside the gearbox or motor? (rhetorical)

I worked on a motorcycle project a couple of years back. We were breaking all sorts of parts and then realized that there wasn't enough "give" in the system and the shockloads were being relieved by parts breaking (hubs, chains, sprockets, crankshafts).

This is similar in concept to why solid motor mounts are bad for daily use cars. You and I "feel" the added vibration and it's uncomfortable. The car "feels" the vibration and starts to come apart over time.

[bigchillcar]

razorracer,
i'm wondering if i don't have the same problem. i need to go back in my records and see when the clutch job was last done and try to tell if i have the rubber centered or spring version.

anyway, it feels like i have a significant amount of what i call 'preload'...if i just tap the gas pedal, it clunks...kinda like what i remember about old, worn out u-joints. does yours do this? once it's loaded, it doesn't slip...just annoying as i initially tap the gas when it's in any gear.
ryan

re-posting this...really thinking we have the same issue. mine's been like this for nearly a year i think, not sure though...it's gradually been sneaking up on me i think.

[juanbenae]

i have heard conflicting stories on this subject. on topic but, not exactly. i have had two very highly recommended wrenches give me two different takes on the rubber centered clutches.

one saying that (my ppi guy) "if one lasted more than 30K miles we would have hung it on the shop wall as a trophy". i asked after the ppi specific if he thought my clutch was a stock rubber centered unit. with his statement above he said more than likely with 64K on a 78 (2+ years ago, 25+ year old rubber) no, it probally had been replaced.

My current wrench says they may last as many as 73K and 28 years (my current state of affairs). I took it to him after i did a clutch cable and adjustment when i statrted experiencing some take off low rpm chatter. he drove the car and liked the adjustment. in speaking further i revealed it had been on ramps (front wheels) for about a week before i noticed the chatter while doing some valence work. he stated it was more than likely a main seal leak and oil/swepco had gotten on the clutch plate. it did go away after about 100 miles and has been not problem a since. that would include very spirited mountain driving.

so my question which is it? 30k as a record, or possibly do i have a rubber center still on board?

sorry to take this in another direction

[RazorRacer]

chrisp, once the clutch is engaged, there is no additional stresses and we can avoid the lurching, too.

bigchillcar, I think we do have the same problem, but I'm still not convinced it's a worn rubber part. Have you checked for worn CV joints? That's the first thing I checked. It's something in the clutch for me.

k911sc, welcome. you would think that this problem has been discussed and become well known, but apparently not.

[bigchillcar]

razorracer,
lol...let me give you my list of recent efforts to try and solve this:

brand new, complete half shafts...thus, yes, new cv's

brand new, sport tranny and motor mounts...

the only things left conceivable would be clutch or worn ring and pinion gears...what else could it be producing such noticeable slack in the drivetrain until loaded?
ryan

[RazorRacer]

Agreed...you and I have the same problem. My trusted wrench says there's too much slack for it to be in the transmission, so it has to be in the clutch.

[Mike Kast]

Originally posted by k911sc
so my question which is it? 30k as a record, or possibly do i have a rubber center still on board?

sorry to take this in another direction

I drove an SC recently that had a rubber clutch. If I remember correctly it had about 50,000 miles on it. When I was still looking for a 911 a year ago I found one in Pennsylvania that had just under 100,000 and the owner said it was an original clutch car with original chain tentioners and no pop off valve.
So... I don't have any hard evidence, but I wonder if the ones that have survived the doomed 30,000 mile period we have all heard about live out a normal clutch lifespan or if the few that are left are just freak rarities. or both?
Either way, It seems they are all due to be changed about now.
Did the rubber clutches perform as well as a standard replacement clutch? Or better? Or no noticeable difference?
The one I drove a couple of months ago was a dog! I don't have a clue what about it made it feel that way, but the car just felt weak. I thought the low mileage on it had somehow taken its toll but I have no clue. It was immaculate looking but weak.

[bigchillcar]

razorracer,
yeah, i've had this problem a long time, too. i'm going to order the parts and try to do it myself pretty soon. it feels like i could probably go for a while like this, but it's annoying as hell...hit the gas in any gear and it feel the clunk before it loads, i guess it's that slack.

i can feel it transmitted all the way through to the shifter knob if i leave my hand on it...you too?
ryan