I just did a C6 to zf5 swap in my 86' 6.9. Someone told me to use a 6.9, 4speed flywheel behind my 6.9 for balance purposes (bullcrap, you can use the SMF conversion or the 7.3 DMF on the 6.9). I did and modified my clutch fork to compensate for the thinner 6.9 flywheel (I work at a welding shop and was able to figure it out, but this is why everyone says the 4speed flywheel won't work). I basically built up/spaced up on both ends of my clutch fork as the pressure plate fingers are further away from the TO bearing because of the thinner 6.9 flywheel. See pics of stock fork and modified fork; plus pic of installed fork up against the back of the TO bearing. It worked fine. It actually revved quicker as the 4speed flywheel probably weighs half to 2/3 of the DMF.
It worked *****'n, no problems what so ever, except for the amount of gear roll over noise coming from tranny at idle. It wasn't that bad in the cab, but as soon as I opened my door it got loud. When driving, no noise at all as soon as rpms went up a little. It bugged me too much so I found a used DMF and now it's quiet at idle and all I hear is engine and exhaust. With the 4speed flywheel, I ran the clutch disc with only one set of springs. I bet if you got a single mass conversion clutch disc with two sets of springs, it would quiet it down some.
So I have basically everything else you need to get your conversion rolling:
freshly surfaced/machined 6.9 flywheel, with new USA input shaft bearing installed
used clutch disc (but I'd recommend getting the dual spring clutch disc to prevent excessive noise)
used pressure plate
used TO bearing
used master + slave cylinder I got with my zf5 (I bought new units, but guy said they worked)
modified clutch fork to make all these parts work together
I'd make you a deal on all these parts, but shipping is going to be expensive as I'm in CA. The $232 SMF conversion kit is so cheap, but I've seen more bad reviews than good ones. There's another SMF conversion kit for $300 that has good reviews, but I guess it depends on your budget.
Hit me up if you're interested or have any questions. I'd be happy to help as I also replaced my 6.9 with another low mile, rebuilt 6.9 at the same time. I'm finally getting this 4x4 dually flatbed up and running. Bought it with bad motor almost 15 years ago!! Also have two diesel, 85' and 88' parts trucks.
Chris
805 748 8564
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