As many know, I recently replaced my oil soaked clutch with a rebuild by Southland Clutch in San Diego. They machined both surfaces fairly lightly (I calculated a total removal between the two surfaces of 30 thousandths) and replaced the friction material on my OEM disk.
I had to return the disk for replacement of a bad rivet that Eagle Eye John Zeiler caught, but otherwise things looked good. Unfortunately, the results after assembly are less than satisfactory. The very first time I engaged the clutch, it had a severe {shudder, judder, chatter} (I see all three used to describe this phenomenon) with the engine at idle and in my garage on a level concrete floor.
I thought it might just be a high spot that needed to be worn in a little, but I dropped a note to Southland anyway. They said this was not normal and asked me to get back to them after a significant number of starts have been made. I have run nearly a full tank through and made probably 50 starts now, all fairly easy at RPMs varying from just above idle to 2,000 or so. I thought the other day that the shudder was gone as I rode nearly 40 miles and it didn't occur once. However, just as I was leaving the last stoplight before my house, it shuddered heavily. Since then, it seems to shudder more when cold and less when hot, but it is fairly random. Hard to believe something like this can be random. When it is smooth, it is really smooth just as smooth as it was before the rebuild.
I tried to get it to do this earlier today so I could get it on video while I had my wife with me to run the camera, but I could not get it to shudder no matter how easily I engaged the clutch. However, I washed the LT and when I went to move it into the garage, the shudder was back with a vengeance and I got it on video. I was along, so it had to be done at idle with me riding one-handed.
The shudder is worse at idle or low RPM and if I rev to 2,000 or so, it doesn't audibly shudder or chatter, but I can feel a slight pulsing as the clutch engages. However, at other times, it will be as smooth as silk. I am including a link to the video and I think you can easily hear what I hear if you turn your volume up.
I have read several articles on this and they give a range of possible causes, but I think I can rule out almost all of the causes other than improper machining by Southland or an improper friction material. Other causes, such as oil contamination I ruled out as this happened the very first time I engaged the clutch and I had cleaned the parts several times prior to assembly per the Clymer manual and I was quite careful as to how much grease I put on the splines and pressure plate pads.
Anyone have any other thoughts as to possible causes? I can't think of any assembly errors that would cause this, but I don't want to point a finger at Southland if there are other equally likely causes. I have not seen this before personally, but as I read more I see this is a fairly common issue with some of the new automatic DCT cars and can be do to oil contamination, improper friction material (I found a pretty interesting research paper on that topic alone) and software that doesn't engage the clutches properly.
I probably won't bother to tear it down again as the clutch works great otherwise. It disengages fully, shifts smoothly, and holds full throttle torque. If I remember to rev to 2,000 or so to launch, the chatter is nonexistent and just a light pulsing occurs. I normally wouldn't like doing this, but since the only fix now is to replace the clutch cover, pressure plate and friction disk, I am not too worried about damaging them as I have nothing to lose.