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Technical School me on Flathead Ford flywheels

Discussion in 'Traditional Hot Rods' started by breakdown, Apr 5, 2014.

  1. breakdown
    Joined: May 24, 2007
    Posts: 136


    I have an older running early 1940s Ford flathead that has a crusty flywheel with two planes? on it. I also have a lightened flywheel that is completely flat. I would like to use the lightened one, but I have a couple questions pertaining to this. Are all flathead flywheels the same diameter, as I think the lightened one is off a truck? Also, the lightened one is drilled for a larger clutch/ pressure plate, is there any consequence in redrilling it for a smaller clutch and pressure plate? Lastly, is there any benefit to using the flywheel that has two levels vs. a flat one?

  2. jetmek
    Joined: Jan 12, 2006
    Posts: 1,847


    the dished flywheel is somewhat heavier and uses a 9" clutch the flat one will work if off 42-48. 49-53 will not work and uses an incompatible pressure plate 10" is desirerable 11" truck not so much
  3. FlatJan
    Joined: Dec 13, 2013
    Posts: 212

    from TX

    i also have a flywheel with 11" clutch.. How much can I lighten it with a 4"crank 2x2s hiconp heads if I want to use a hot cam?
    any recommendations?
  4. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,612

    Bruce Lancaster

    Early ('32-48) flavors: 1932-4 used a wheel with a heavy rim drilled for the pressure plate bolts...pressure plate bolted to the rim well above the main surface, friction surface was down on the main surface. Same basic pressure plate as Model A.
    1935...Ford went to the common Long pressure plate, 9" for passenger cars. Many of these wheels also had a rim ring but had no bolt holes in that ring...pressure plate bolted right down to the friction surface within the ring. This flywheel was commonly used to make light wheels, as just machining off the ring dropped a lot of weight and tapering the edge cut some more, plus it took the light 9" clutch. Trucks got 11" Long on a heavier flat flywheel. I think this rig applied through about '42. After then, all flywheels were flat, and since the cars were picking up weight the pressure plates went to 10" Long for cars. In '35-48 the 11" was also an option for heavy duty (like Taxi use) cars, and the bell portion of trans from '35-48 was slightly reshaped to allow all versions to fit.
    '49-53 wheels do not interchange with earlies, and came in 9 1/2, 10, and 11" Long and in 10" Borg and Beck patterns. Some were drilled for two sizes.
    FlatJan likes this.
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