Pressure Plate

[Mijostyn]

Hi Everyone and Happy New Year!

 

While driving My C4S last week around town the clutch pedal stuck to the floor! I stomped on it and it finally came up. After that the clutch felt really light and when I depressed it I could feel the engine in the pedal. The clutch would engage but if I gave it too much gas it started slipping. The car has 49K miles on it now. I limped it over to my indy. It is supposed to come apart today. My guess is that the pressure plate broke. I have never heard of this happening before. Anyone have this happen??

[JFP in PA]

1 hour ago, Mijostyn said:

Hi Everyone and Happy New Year!

 

While driving My C4S last week around town the clutch pedal stuck to the floor! I stomped on it and it finally came up. After that the clutch felt really light and when I depressed it I could feel the engine in the pedal. The clutch would engage but if I gave it too much gas it started slipping. The car has 49K miles on it now. I limped it over to my indy. It is supposed to come apart today. My guess is that the pressure plate broke. I have never heard of this happening before. Anyone have this happen??

 

Yes, and yes.  These are diaphragm style pressure plates and have pivots (fulcrum rings below) for the fingers which can fail, or the diaphragm itself can fail.  Not a common failure, but it does happen.

 

[Mijostyn]

Nice diagram and Thanx! I did not hear from the Indy today. In looking at the diagram my guess is that the diaphragm spring broke. I'm the third owner of the car. The second owner tracked it for about 1000 miles and beat the poop out of it. I've already replaced wheel bearings and struts. I guess this is another manifestation of the abuse. I expected the clutch to die prematurely just not this way. Hopefully the flywheel is OK. Can you resurface these? I won't put a light weight flywheel on the car from all I've heard. While its apart I'm redoing all the engine and transmission mounts and replacing the shifter console and cables with GT3 style versions. 

[JFP in PA]

1 hour ago, Mijostyn said:

Nice diagram and Thanx! I did not hear from the Indy today. In looking at the diagram my guess is that the diaphragm spring broke. I'm the third owner of the car. The second owner tracked it for about 1000 miles and beat the poop out of it. I've already replaced wheel bearings and struts. I guess this is another manifestation of the abuse. I expected the clutch to die prematurely just not this way. Hopefully the flywheel is OK. Can you resurface these? I won't put a light weight flywheel on the car from all I've heard. While its apart I'm redoing all the engine and transmission mounts and replacing the shifter console and cables with GT3 style versions. 

 

Dual mass flywheels cannot be resurfaced; doing so would cut into the elastomer which would ultimately cause the unit to fail.  Your current flywheel can be cleaned and the surface buffed with something like a Scotch Brite pad, but that is about it.

[Mijostyn]

Well, He has the car apart and the pressure plate is junk. He relates that the flywheel "is a little loose" but is neither for or against replacing it. I'm more on the replace it side. JFP what do you think?? Also should I replace the RMS while we are there. Mine is not leaking now but I understand there is an upgraded part for this engine.

 

In the middle of a BIGGG snow storm. Skiing is going to be GREAT!!

[JFP in PA]

It is kind of hard to tell what he (or she) is referring to by "a little loose".  There is a factory flywheel testing procedure where you determine how much you can twist the dual mass and if it returns correctly; if they have use this procedure and it is either over the limit or does not return properly, scrap it.

 

 

DualFlywheelTechBulletin.pdf

 

[Mijostyn]

Yes, the DMF turns like 2.5 cm side to side and is a little "sloppy" but There was no unusual transmission noise. 1st and second gears are not shifting well but I think that is do to worn cable ends. I am replacing the Cables with GT3 style ones with metal cable ends and the entire sift console with an all ball bearing aluminum one. Also what about that RMS issue. Would you replace one that was not leaking while you were in there doing the clutch? 

[JFP in PA]

The important point on the dual mass is that it twist no more than 15MM in each direction, and then when released returns to its original position.  If it moves more than 15MM, or does not return, it needs to go.

 

We always replace the RMS whenever we have a car apart; it is less than $20 and takes 5 min. to do, but cost a whole lot more time and effort to get at it again.  The newer PTFE seals are much better, but require that all surfaces be perfectly straight and clean, not even finger prints, and that the seal be installed 13MM from the flywheel mating face on the crank.

[Mijostyn]

I went to see the car this afternoon. The flywheel definitely went more than 15mm, more like 25mm. It did return sort of to center but there was some slop around dead center. It's going. I always though the clutch in this car felt numb in comparison to the other 911s I have owned. I wonder if that was why.

It is a little "damp" under the RMS and there have been two updates since this car was built. Along with your logic clinches it for me. This indy has the appropriate tool so I am not worried. The was an old Lambo Diablo on the lift next to mine that just had an engine rebuilt. Boy what a nightmare it is under that car. That god for 911s!  Could I have done the clutch. Ya sure but on jack stands I would have hated every minute of it and would have always wondered if I got it right. Now having seen what it takes I might try it next time....if I ever get that lift.

[JFP in PA]

13 minutes ago, Mijostyn said:

I went to see the car this afternoon. The flywheel definitely went more than 15mm, more like 25mm. It did return sort of to center but there was some slop around dead center. It's going. I always though the clutch in this car felt numb in comparison to the other 911s I have owned. I wonder if that was why.

It is a little "damp" under the RMS and there have been two updates since this car was built. Along with your logic clinches it for me. This indy has the appropriate tool so I am not worried. The was an old Lambo Diablo on the lift next to mine that just had an engine rebuilt. Boy what a nightmare it is under that car. That god for 911s!  Could I have done the clutch. Ya sure but on jack stands I would have hated every minute of it and would have always wondered if I got it right. Now having seen what it takes I might try it next time....if I ever get that lift.

 

I fully understand the complexity of the Lambo, we just had a new Ferrari 488 Spider up in the air and it looked like more moving parts than the space shuttle under there with their active aero stuff.

 

Doing the clutch on the ground is really not all that bad, the only real issue is the flywheel bolts; 19 ft. lbs. plus 90 degrees.  The last 45 of those 90 can be murder unless you are built like King Kong.  I actually walked out into the shop once to see an intern literally hanging on his longest breaker bar with his feet off the ground. Not fun....

[Mijostyn]

At 64 I'm not in bad shape but King Kong I am most definitely not although my wife might disagree (Viagra:-). I think I'll wait for the lift. Anyway with entirely new internals I should be able to make it another 100K before it has to be done again, about 10 years.