Clutch Replacement
 

Looks like I'm coming to the point where I'm going to need to replace the clutch in my '94 C2 Cab. Since I'm replacing it anyway, is it worth it to upgrade the clutch or should I just put in a factory replacement? What is the cost difference between upgrading vs. the factory version?

Thanks,
Scott

Hi Scott,

With regard to light weight flywheels (LWF), there is a current, very informative thread on the 993 board. In a nutshell, since you have a pre-OBDII 911, you run the risk of having idle/stalling problems with a LWF. Two solutions are Andial's "semi-light weight" flywheel and a software modification.

Unless you need a "competitive edge" (tracking?), I would suggest you stay with the factory stuff. Makes for a good daily driver.

An important point. When you have your clutch work done, prompt the mechanic to lube /seal your input shaft/clutch center, along with installing all the tranny plugs. Myself and another person on the 993 board had to have our transmissions pulled recently, because of a sticking-in-gear problem. In both cases, rust was found on the input shaft/disc center, which caused the binding. In my case, standing water was actually found in the case, as the last mechanic to work on the car failed to reinstall the bell housing vent and slave cylinder cover.

Finally, my complete clutch job (sans flywheel, I have the LUK) only cost $1210. I had received estimates anywhere from $1200 to $1500 (independent) to $1700 (dealer) to $2100 (an independent shop) to $2600 (another dealer). The shop that finally did the work saved on labor costs by only dropping the tranny. According to the mechanic, many shops don't know you can drop the transmission only, and still drop both the engine and transmission.

Hope this helps.

[ 07-06-2001: Message edited by: Randall Granaas ]

I LOVE my LWF, but it does come with a price.

Usually stalling only occurs shortly after startup...when backing out of a parking space or the first stop before leaving my neighborhood, otherwise, not a problem.

I have been told by many that a modified IDLE STABILIZER or a reprogrammed chip will make the fix...seems my research more favors the idle stabilizer...but if a chip will add more HP and somewhat fix the stalling issue...it's "more bang for your buck" that will do it for me.

I wouldn't count out the benefits of the LWF/clutch upgrade...the car accelerates quite a bit more now, only from the gear you are in at the moment though...it's quite fun.

Do your homework, I would NEVER put in a factory/stock clutch/pp/flywheel setup, but that's just my "performance minded self" talking.

With the sporatic issues that the LUK flywheel and the p.o.s. dual mass flywheel that came in '89-'91 964s have...consider an aftermarket alternative, they are proven, as well as cheaper in some cases. Happy Hunting! :D

[ 07-11-2001: Message edited by: Jeff Curtis ]

Dear Jeff,
Just a small but critical correction. Dual mass flywheels were introduced in the 1990 model year for the C2 and the C4. The 1989 model C4s did not have the dual mass flywheel,
Ciao,
Adrian
911C4

PS: Check out the stuff on offer from Tweeks. The question was on the clutch and you can improve the clutch without changing the flywheel.

The current issue of Excellence magazine features a road test of a supercharged '95 993 with LWF. They (the staff of Excellence) stalled the car 15-20 times during the 2000 or so miles they had the car. They felt it was an acceptable trade-off for the benefits of a LWF. Not so sure of that myself. Used to have a LWF in my car. Loved the way it revved, but couldn't tolerate the inopportune stalling. Then there's the embarrassment factor :o , when you stall your P-car in front of a crowd of people as you're pulling into the local Italian restaurant.

I was surprised that no attempt (at least not that the article mentions) had been made to remedy the stalling (e.g., software mods). The article does mention that the stalling can be remedied by adding 4 pounds back onto the flywheel, but that this partially negates the benefits of the LWF.

[ 07-11-2001: Message edited by: Randall Granaas ]

These are just my opinions, so take them for what they're worth:

1. The 993 and the 964 shouldn't really be compared at all. The 993s have completely different engine management systems, not to mention engines...sure they're both 3.6 liters, but the 993 uses different pistons, hydraulic lifters, a different cam, and may have Varioram depending on the year.

2. Because of #1 above, the way a LWF acts in a 964 compared to a 993 may be two different things. I've heard stories ranging from total success to total disaster regarding the 964 with a LWF setup. This MAY not really be dependent on just the chip itself. Porsche likes to upgrade their cars the way software companies like to upgrade their OS's. It may depend on what is on your car and what assumptions the software writers of a chip may have made regarding what is actually in a car. I think a good example of the radical difference just between years is the fact that the very early 964s have no check engine light (here in the US) but others do.

3. This point may sound somewhat obscure to people, but the CPU in the engine management system may actually be limited in it's sampling rate of things like the RPM sensor between various years (I don't know if this is true or not) by it's speed. I would have to assume that the newer the car is, the higher the CPU clock frequency would be, and hence it would allow a much higher sampling rate of the sensors. This may not be true from one 964 to another (but it may be), but I would think it would almost be certain when comparing a 964 with a 993. A higher clock speed for the CPU means the CPU can sample the various rates it's monitoring that much faster, hence it stands a better chance of correcting for some of the oddities that a LWF may introduce.

Like I said, just opinions and a fair amount of speculation..take them for what they're worth,

Bill Wagner
'91 C4

Good points you make, Bill. Did you read the recent thread on the 993 board, titled "Lighter Flywheel," topic started by Jim_me, last "updated" 7/3 @ 2156. Lots of great information, but one post made by Steve Weiner is especially enlightening. I've copied the text of this fabulous post below:

**************************

Hi Gents:

Like many things in the world of Porsche, this might not be for everyone but its definitely a performance enhancement with few operational drawbacks and does improve durability. Up to now, the stalling issues with the unweighted ones, made this something to think about for street use. This has
now changed.

A few points here:

1) The worst offenders for stalling problems were the 964 series and the '95 OBDI 993.

2) The '96 and later 993's are OBDII and these cars seemed to handle the RS light flywheel setup without much trouble unless there was something else wrong. Carboned up throttle bodies and idle stabilizer valves come to mind. This software modification is not needed on the OBDII cars.

3) We originally fixed the 964 stalling issues with a modified idle stabilizer
that did the trick. This also worked with the '95 993 cars.

Now, we do the same thing in software and this is usually done when the DME is reprogrammed for more performance. No more stalling troubles!

Andial's RS flywheels with the additional weight added also took care of this
problem. We simply wanted to preserve the lighter weight aspect and retain all the benefits and therefore required a software fix.

There is no question that the lack of flywheel mass and damping makes the typical G-50 low speed gear rattle more audible and for some people this is not acceptable.
This IS a performance upgrade and this is the only real compromise that I can think of.

Personally, I love it and when combined with a good set of close-ratio gears, this REALLY makes these cars perform without affecting emissions compliance or causing check engine lights,....

--------------------

Steve Weiner
Rennsport Systems
Portland Oregon
503.244.0990
http://www.rennsportsystems.com/~porsche/
porsche@rennsportsystems.com

**************************

"Jeff's" idle stabilizer mod is mentioned in this post. And, I'm guessing that the reason the OBDII car's handle the LWF better is because they're "smarter/faster" than the pre-OBDII ECU's, as Bill speculates.

The supercharged '95 in the Excellence article pretty much behaves the same way my '91 (pre-OBDII engine) did with the RS LWF. Great revs, lots of stalling. When I had the LWF in my car--back in 1995--there apparently was no fix for the stalling--or at least my mechanic(s) didn't tell me so.

Finally, one more interesting tidbit gleaned from the 993 board thread. An OBDII 993 owner had a LWF w/Porsche Motorsport clutch installed his car, no problem. His friend put the exact same set-up in his '95 993--car stalled "all the time." He wound up adding Andial's weight to the flywheel to fix the stalling problem.

hi,
I have a '91, I installed a new andial unit with the added weight(due to failure of original)it already had a computer chip, its been 2 months now and It HASN'T stalled, not even once. Sure, there's a little more gearbox sounds, but for me its a trade off I can live with(cause its not as bad as some make it sound).........Geo.

I don't remember being irritated by excessive drivetrain noise when I had my LWF ....

Geo, glad to hear your "semi" LWF works well.
Andial claims they don't have any stalling problems with their modified LWF, and I tend to believe them.

Thanks for the great posts fellow 964ers! :)

I have a Freudenberg in mine and the odds are that little sucker will fail sometime within the next few years...maybe days...who knows!?!? Maybe it will last 100K.

I've never liked the DMF idea. Roland Krunz and I had a rather lengthy discussion on the old Rennlist site about this. He said, if I recall correctly, was that the REAL purpose of the DMF unit was to unload strain exerted between the clutch and flywheel on the engine bearings (Roland if I worded that incorrectly, feel free ....no PLEASE correct me). Another function was noise reduction. From Paul Frere's book, I get the impression that the priority goal wasn't reliability but noise reduction.

Noise reduction? WHO CARES! I would rather have a performance gain AND better reliability at the cost of noise reduction. How many '89 C4s (which use a solid flywhel) are having their engine bearings fail prematurely anyway?

I think the DMF was Porsche's first step in the "yuppyization" of the 911 series...which continues to this day with cars that are unserviceable by their owners!


Bill Wagner
'91 C4

Besides Roland's post, I have also read elsewhere that the other function (besides noise reduction) of the DMF was to enhance engine durability-or something to that effect. Don't remember where I read this, but I think it could have been Bruce Anderson, maybe other places.

Interestingly, this second "benefit" of the DMF often goes unmentioned, even by acknowledged experts such as Steve W. Seems they don't consider it to be very significant.

If I knew two months ago what I know now--that OBDII cars handle DMF's so well--I might very well have had a LWF put in my car during the recent clutch replacement. If my LUK ever does give up, I'm pretty sure I will go LWF.

My original 964 engine did spin a rod bearing at 100k miles, but I seriously doubt it had anything to do with the 17k miles or so the car ran with a LWF.

Hello

Well old stories again.

Now sit in your office chair and spin youself. the push ellbows and later your arms out.

Now make the same but have a big phonebock in your arm.

The Phonebockeffect is achived with the Andial solution.


And just some inputs again.

Porsche did reduce the wight from the 964 crank at some 10% and came into a critical break area. So they had to get rid from the low end vibes/distorsion by adding on balanzers on the ends.

In fact the 964 on cranks are a thad weaker then the previous cranks. But the lowerd wights from the crank driven parts did compensate that.

If someone has time he will find that in any good book about the 964.

If you had the cranks in your hand you will feel it.

The crank has two sides to drive. One is the clutch and a centered force the other side the belt drive an off centered force.

The off centered forces twist the end from the crankshaft, they pull it upwards. The force is not only several pound generatet by the tension from the units. You have a fan plus a alternator who will pull some 40 HP under full load plus the air condition compressor with some 10 - 15 HP at max.
That is the power Porsche #356 0001 delivered on the crank to propel a 600 kg car in 13 sec to 60 mph.


Now those units also have masses like the flywheel and hard to accelarate or brake.

The trick to keep the crank unstressed was to use a dual mass flywheel on both ends. Those units are torsion dampener and they will twist ( up to 60° ) under load making the engine spin "free" or like floating in free ends.

Now back to your office and fetch the books again. Reach aout your hands and rotate them synchronized with the books or Coke bootle or your gym wights. Got that feeling. next step is rotate only one side. Now this is how the engine feels if you have the accesory driven on one side while you have a LWF on the other side.

No not direct as the engine has the situation as you would like stand one one foot.

Waht else ?

If you delete the DMF the engine will hang direct on the string from the car.

Now this is like comparing an automatic to a stickshift. If you rebuild engines you allways will find lees wear in automatics. the reson is that the automatic damped the loadchanges when you go from on to off or from off to on throttle. On a stickshift this is like hammering on the engine. Now the next point are the gyroskopical forces.

If you spinn something it will get more mass or kinetc mass. There is a balance beetween the wight from the crank and the mass by spinning it relatet to the car. The crank musst allways have a higher mass then the car to be the winner in the "hammering" game.

Now the 964 got a bit heavier and therfore the mass in the crank had to go up to egoual that. But Porsche was over that limit since the 80´s 3,2 and used that rubber torsion damper to stretch the limits.

But the good news are your engine will not get to much hurt as the trany is beetween the tire/bodymass and the engine mass.

That shattering is when the two masses colide on one point exactly a oval pressure zone from the gear. Now just look at a bell or a triangle with a dongle beetween two ends.

Now transmission gears where made for a constant load but not dynamical forces. Also the bearings got knocked by hammering.

To explain the difference get into your kitchen and take two oranges. But them both on the floor and then stand on one and try to press it flat. Done ? Then go to the next and just jump on it. Big mess ?

Orange juice does clean the floor very good and your wife will be impressed about the shiny kitchen.

Now you can imagen why Porsche made a fuss about that. The limits are very high on a bullet prove level.

Now why is the engine stalling ?

The reson is that Porsche programed the motronic to rev soft onto the DMF ( to keep the load on that smoth ). With the free floating crank you had someting like 50° dwell angele time to speed up the engine but with a LWF the engine has to react much faster and harder.

Everything clear ?

On the newer Motronic Porsche has more brain integratet lets say the ECU was in real time mode and worked with direct feedback.

Just an other side note:

The Freudenberg DMF was used on BMW and many from them have now DMF failures like Porsche had it. BMW says it is a normal waering part like the friction plate. BMW never hat the intention that the DMF would hold the cars whole lifespan.

Most american owned have a automatic and doesn´t seem to use the sticks to hard.

Grüsse

Roland:

A lot of people want to move AWAY from the dual mass flywheel not because they are after what you seem to consider is a risky performance enhancement, but rather to get away from what many see as a low quality, poorly designed flywheel. The LUK is certainly an improvement over the Freudenberg, but take a look at this link:
http://carpoint.msn.com/Vip/UsedRelO...e/911/Used.asp

As far as web information regarding problem reporting goes, that site is about as good as I've seen (good web information usually translates to fair when applied to the real world, in my opinion). Our cars tend to not be driven as much as most other cars, hence it takes more time for a problem to crop up. With this in mind, the dual mass flywheel appears to still be reasonably questionable, even if it is a LUK. Will the LUK be better? My guess is that it will be much better than a Freudenberg, but is it still as good as a "solid" flywheel. I'm suspicious of this.

Here are some questions for you:

1. Since the 1989 C4s are all using a single mass (solid) unit, are the early C4s having premature engine failure because they don't use the dual mass flywheel?

2. Is there some type of difference engine-wise between the 1989 C4s and all the following model years (for example, different crankshafts and bearings) that would allow the early C4 engines to hold up better with a "solid" than later C4s would?

Prior to buying a 964 I did a lot of research into the cars. My OPINIONS AND OBSERVATIONS are based on owner reports that imply the dual mass units, in my opinion, leave something to be desired. By the way, I capitalized "OPINIONS AND OBSERVATIONS" to make it clear to everyone that I don't have thousands of trouble reports at my disposal and I'm basing my information on samples of probabably no more than 100-200 units...perhaps I should ask Porsche for failure data, but I bet they won't give it to me! :(

My trouble with the dual mass flywheel is that theoretically it sounds like a great idea, but I question whether or not the implementation of that theory was really very good. Theory and implementation are two totally different things.


I'm looking forward to your opinions,

Bill Wagner

'91 C4, 21K miles, Freudenberg entact and OK, so far!

Dear Bill,
According to the documentation I have from Porsche and from the Swiss authorities the prime purpose of the Dual Mass Flywheel was indead to reduce the transmission noise levels which were still outside the limits with the 1989 C4s. From a totally biased point of view. I think the 1989 C4s are a little bit more bullet proof than the later ones. A quick check of the parts catalogue show the 1989 C4 to have quite a few different parts to the 1990s and on. More in common with the 3.2 actually.
Ciao,
Adrian
911C4

This post fell silent, so I thought I would revive it by adding another post.

Do the '89 C4s have an unusually high failure rate with their engines. If not, then how different are their engines from a 90+ C2/C4...particularly with respect to the bearings and crankshaft.

Thanks in Advance,

Bill Wagner