Let me start by saying that this is a steep learning curve, with tiny margins of error allowed for success. Both ill (ZFdoc) and Jim at PowerTorque are experts and helpful; a rare resource for those willing to listen to them, in this car hobby. We have all met some, purported experts who blow hard about this and that, then blame others for issues that arise. My personal experience is that 90+% of the shops and other 'experts' are dangerous to my car's health.
Jim's initial reply to my clutch questions was very discouraging, but I learned why, when he answered the telephone. He seems to be the go-to guy when ZF projects, especially conversions, 'go south'. Now, as a good guy, he has helped, oft for no personal reward or even compensation. The problem arises when he does so, then the caller disregards what is suggested. Why call an expert, only to disregard the advice?
We ended up spending up over an hour talking. I learned a lot. My project was termed a double conversion as my engine has the two piece rear seal and the 'normal' push type clutch. Besides the ZF employing a pull clutch, most cars have one-piece seals. The seal count is not the issue; the geometry is, meaning more than different bolt patterns and flange sizes.
The longitudinal clearances are critical to a successful install, especially as the ZF needs a 100% functioning hydraulic clutch to preclude synchro and gear damage. They are tough but precise units and their limited deployment is nudging repair costs skyward as parts stocks get depleted or almost worse, get sourced in China. Failures, for example, of the China-made release bearings runs about 10% of the 'real' ones, yet that stock is pretty much gone. Few, it seems, can tell from the part number, which are real and which are Chinese. Similar issues exist in clutch parts choices, as one after another once-reputable U.S. firms sells out their good name. Okay, I digress.
I paid $900, plus shipping, for the reman black label ZF alone. The alternatives are meager and many are unattractive, given the situation in the Corvette ZF arena, meaning boxes in need of repair due to poor hydraulics or incompetent 'repair'. The scarcity of competent technicians and parts, plus the costs, makes used ZFs an iffy proposition. One might imagine the future of ZF-equipped cars as bleak. My own view is that this is true of most of the new cars, regardless of price.
Tomorrow, at Jim's recommendation, I will speak with RAM about their HiPerf single disk conversion package and the special needs for my project. The tolerances, again, are critical to success, defined as smoothness and longterm reliability, w/o having to redo and redo.
Bill gets $700 for a rebuild, plus parts. With many of the larger parts running in the hundreds of dollars, it is easy to see that a cheap transmission, may not be. He is a reputed perfectionist, with attention to details. Who do you want working on your car and when have you seen the cheap route, stay so? Bill will do the install and I will help get this small group of experts on the same page, and LISTEN to them, so my unique C4 stays on the road for some time.
He agreed with my choice of steel flywheel, BTW, but not knowing the particulars of the existing FW, had no advice as to its use. Aluminum SMFs will also rattle more with a lumpy iding engine. Again, that crucial tolerance for full clutch engagement and full disengagement.
There is so much more; so many stories of hack jobs, but this is too long already.