I have also studied the problem of how to handle the high torque generated and passed through the clutch and transmission package. To give the background, I had contacted an ebay seller doing business as GermanPartsWholesale and learned that he had done (does) a number of TDi into Vanagon conversions. He said he had a clutch solution. Asbestos lining of the FW side, feramic face on the PP side for a dual material disk. This he put together with a higher clampforce pressure plate - all at the Vanagon 215 dimension. He said that his tests show that the package on the Vanagon diesel flywheel would hold 350 foot pounds without slipping, but with soft engagement. His price was $189 for the disk, $129 for the modified pressure plate and $40 for flywheel surfacing. He required that I ship him a used clutch disk and pressure plate (he would rework both) and the flywheel.
I then discovered all the negative discussion about him at TDiClub, and his alterego's (www.tdiracing.com and tdinozzleguy). You can see the proffered clutch system on TDiracing.com by going to other products after you reach his web page.
At this point, son and I discussed the story over excellent Steakburgers at Kirk's in Palo Alto. Kid said - why the asbestos on the FW side and feramic (sintered iron metallic brake pad material) on the pressure plate side? GPW said soft engagement on the asbestos/FW face then if overheated, secondary engagement on the feramic PP side. Kid pointed out that moderated engagement happens on the PP side with the FW/clutch face firmly contacted and the pressure plate moving up and down slightly as you feather engagement. So soft engagement surface should be on pp side!
This and the negatives from TDiClub caused me to look further into the problem. I soon found that much of the story was true (except for reversed face materials - I'm now told that this is the case for chinese sourced knock-offs of dual face clutches). I found South Bend Clutch, Inc. These guys (see www.dxdracingclutches.com) build clutches for the truck and diesel truck as well as agriculture market. The DXD site is their retail outlet for passenger car applications including racing.
They sell the feramic material as well as full asbestos material as well as Kevlar, racing organic material, ceramics, etc. They were very high on the feramic material (also confirmed the moderate engagement side of the clutch) because it has smooth engagement, excellent thermal properties, good friction and doesn't cut into the flywheel surface. Further, the guy I dealt with (Andy @ 800-988-4345), clearly knew his stuff. He pointed out that the VR6 clutch/pp combo that the chipped TDiClub guys go to had a clamping force of 1500 pounds @ 228 mm diameter, while the stock Vanagon pp was rated at 900 pounds. Even with standard clamping force enhancement rework, he could only raise the Vanagon plate to 1100 pounds - a more than 25% deficit. He has the feramic material in both puck style (bad for street) and full face styles (good). However at the Vanagon 215 mm diameter, the disk could only be made in a puck version. At 225 mm we had full access to his state of the art materials.
I then measured my spare flywheel, clutch and pressure plate. The details are that the well in the pressure plate measures 227 mm at the top, 222 mm at the bottom. The bolt circle ring annulus width starting from the inner edge of the starter ring to the edge of the well is 14 mm. The well can be opened to 230 mm without any infringement on the bolt circle for the pressure plate. On the flywheel, there is a 1 mm d-shaped groove surrounding the hardened face. The hardened face is 221 mm OD.
With this data, I have arrived at the following conclusion: Racing 6 spring sprung hub rated for more than 400 foot pounds torque to break, 350+ for start/stop usage. (Hub is 13/16 - 24T), with organic asbestos/brass weave racing face material (M808) for pp side, full face feramic for the FW side. Clutch will be 225 mm with Marcel section. Flywheel will be opened up to 228 mm for center well clearance. I send him the flywheel and he does the cutting, resurfacing and balancing acing. The cost for the clutch and pp combo is $325.03 and the FW machining is $40.
To summarize, Vanagon diesel flywheel opened to true 228 mm ID, custom dual face 225 mm clutch disk with Vanagon diesel pp clamp force set at 1100 pounds for $365.03 plus shipping. More than 350 foot pounds anti-slip capacity with smooth engagement. Note, 15% higher clamp force and higher stiction material to make up performance difference to equal 228 mm Corrado VR6 standard.
