Single mass flywheel?....Sounds pricey...
....Not sure what the difference is?
There's a lot of debate over which is the better choice. I'll try my best to give you a condensed version, but you're really best off searching the forum for some of the threads dealing with the subject.
I'll start with the dual mass flywheel. This was what Ford installed from the factory, and is still what they recommend. It's actually two pieces of metal. One piece of metal bolts to the crankshaft; the other has the clutch bolted on to it. They're connected to one another by 6 sets of heavy-duty springs, and the idea is to dampen some of the vibration from the engine so the vibration is not carried to the tranny. However, it is possible for the springs to break, and if they do, the end result is two separate pieces of metal, and no way for the engine to transmit power to the tranny...and you're stuck. They're also ridiculously expensive to replace with a new unit ($1200 from
www.partsamerica.com, compared to about $500 for a single-mass flywheel).
The single mass flywheel is far simpler. It's a single piece of metal that the clutch bolts onto and that bolts onto the crankshaft. It's lighter, less expensive (compared to buying a new DMFW), and stronger. However, at low engine speeds, you'll get a noise (commonly known as gear rollover) from the tranny with an SMFW that is generally not present on a DMFW. Also, it has been hypothesized that the added vibration from the engine that isn't dampened by a DMFW will eventually have a long-term negative effect on the tranny internals. To my knowledge, however, that has not been proven.
There's also a third option. If you can find a used DMFW in questionable condition, but with a good clutch surface (IIRC it's not advised to resurface a DMFW clutch surface, although I don't know why and may be mistaken), you could try a
Lucky Mod. Personally, I'm not a fan of this method, because the end result is relying on a number of fairly small Grade-8 bolts to transfer your engine's power to the tranny (and, if the bolts break, you're just as dead in the water as if the springs had failed), but others have tried this with success.
I went with a single-mass flywheel myself, and haven't had a problem. However, I've only driven my truck about 15K miles since switching transmissions, so I cannot speak either way about the long-term effects.
The first two pictures are of an old DMFW...you can see both sides of it. The third picture shows the clutch side of a SMFW, and the fourth compares the thickness of a ZF flywheel with that of a flywheel from a T-19. I've heard that someone tried to use a T-19 flywheel with a ZF, but I don't remember if it was successful or not, and in any event, I think it's probably going to be more trouble than it's worth.
or....
