Automotive flywheels are often designed as two-masses flywheels to optimize the oscillating behavior. Both parts are connected by a spring system, which gives the possibility of adjusting the spring stiffness due to the specific engine (and drivetrain) characteristics. In addition, the flywheel is often used as one part of the clutch system, and it may carry the gear for the engine starter. In this way, the flywheel consists of several parts, made of different materials. Here are some links: 

http://www.zf.com/corporate/en_de/products/product_range/cars/cars_dual_mass_flywheel.shtml

http://www.luk.com/content.luk.de/en/products/dampers/zms_sv/zms_sv.jsp?

The flywheel main body is made of steel with no advanced requirements, e.g. S235JR. The gear rim for the starter is a press-fit mounted part made of heat-treatable steel with increased carbon content, e.g. C45E.

Automotive gears are made of steel, too. Depending on the requirements regarding strengh and wear, different low- or high alloyed types come to use, e.g. C45E, 42CrMo4. In some cases, steel with a good producability comes to use, e.g. 11SMnPb37. Case-hardened steel gives the possibility to achieve relatively hard surface (low wear) and elastic inner area at the same time, e.g. 16MnCr5.

Automotive propeller shafts are also made of heat-treatable steel.

Kind regards,

Mario

Gears sometimes are also made in austempered ductile iron.

Franco

FLy wheels are C I castings, machined on o/d face & mtg holes.

Gears are alloy steel comps. Propshaft - from Extruded steel tubes

Propeller shaft - alloy steel tubes to withstand effective torque transmission.

Gears - alloy steel casting or forging.

Fly wheel - Steel castings

 Information unfortunately are inadequate. There are many books about materials in the automotive industry. I would recommend two that I have in my library.

J Rowe.Advanced Materials in Automotive Engineering, 1st Edition

Brian Cantor, P. Grant, C. Johnston. Automotive Engineering: Lightweight, Functional, and Novel Materials.