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    Any difference between a 305 and a 350 Flywheel? automatic.
    Just learned that my new GM motor I put in has a bad vibration. I used the same harmonic balancer but bought a new Flywheel from Napa thought it was the same but it now seems that it is not be weighted or Harmonic Balancer is bad. What do you guys think?
     
  1. Thunder

    Thunder 3/4 ton status

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    If you have an automatic trans its not a flywheel. Its called a flex plate. It may be your problem. A friend of mine put a flex plate off a 350 on his small block 400 and got a vibration from it. When he replaced it with the right one, the vibration went away.
    Take a look at your harmonic balancer. If the rubber in the middle of it is distorted or cracked it should be replaced.
     
  2. 70jimmy

    70jimmy 3/4 ton status Premium Member GMOTM Winner

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    flexplate on 305 and 350 are different. They are not dished out the same. One sits farther from the motor. In my case I have a 350 that had a 305 plate on it. The 350 plate is closer to the motor. After numerous bendix gears being eaten and a couple flexplates I found this out. Diameter is the same. 350 and 400 are different in the fact that the one is externally balanced. I think this was the 400 It has weights on the plate and the 350 doesnt.
     
  3. riz

    riz 3/4 ton status

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    <font color=purple>I bought a new one when I dropped in my new motor, I checked and they said they are all balanced rom the factory.</font color=purple>

    <font color=purple>L8r,

    .Riz.<font color=purple>
     
  4. JimmyDie6.2

    JimmyDie6.2 1/2 ton status

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    I checked in the hollander manual at my uncles junkyard on this. It says that the 305 and 350 small blocks and the 4.3 use the same flywheel. from 79-85. when you get to a 1 piece rear main seal the flywheel is different 86-91. (that manual goes up to 91). So did you go from a 1 piece rear main seal to a 2 piece??? or vica versa???? You will get a vibration!! I personally went through this, especially at idle..................js
     
  5. I went from a one piece rear main seal on a 305 to a brand new one piece rear main seal 350 from GM. I decided to buy a new flexplate and bought it from napa but you know them they never get anything right and they probably just grabbed one for a small block and did not reference the year difference between the two models 2 piece vs. 1 piece. I think I will just go to GM and buy one from them and put it on that way I won't void the warranty I have only driven it a 100 miles so hopefully not too much damage.
     
  6. JimmyDie6.2

    JimmyDie6.2 1/2 ton status

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    another thing about the flywheels, the 1 piece rear main seal is about 4 times the price of the2 piece. (at least at pep boys by me)...........js
     

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