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Discussion Starter #1
Can someone please help. I have a stroker with the 400 crank so, it has a balanced flexplate and balancer. I just put in a new balaned flexplate.

Here's the problem. It runs smooth when its idling. But, when it gets to about 3k RPM it starts to vibrate bad. I don't seem to notice it in 3rd running 3k RPM. But in 2nd and 1st and Park it vibrates real bad.

Help Please

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obnoxious 67 camaro under construction. TH350/383 stroker w/ aluminum Eldlebroc RPM heads,cam, and carb.
 

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Discussion Starter #2
Ill take that back it vibrates in all gears and in Park. Help!
 

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I'm not sure I'm reading yoy're message correctly.
It looks like you state that you had the rotating assembly balanced, including the flex plate. It then looks like you state that you added another flex plate to the assembly AFTER the rotating assembly was balanced. If that's the case, that's probably where the problem lies.
The flexplate should be balanced WITH the rotating assembly.
 

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Who did you purchase your stroker kit through and is it a cast or forged steel crank?

With Speedomotive's kits (and some others) the cast crank kits use the externally balanced (400 style) balancer and flexplate. The forged crank kits use an INTERNALLY balanced (standard small block Chevy) balancer and flexplate.

I read your comments the same as the guy above; it appears you changed flexplates AFTER balancing. As long as you got the correct internal/external balance piece it should work, but you've defeated the purpose of balancing all the pieces together.

By the way, if all the pieces are correct, the balance could be off. I got a 400 from Speedomotive that the balance guy made a mathematical error (his words) and added when he should have subtracted or vice-versa. It shook VERY badly at low rpm's like you are experiencing.

Double-check your parts first and determine if they are correct.

Jody



[This message has been edited by Camcojb (edited 12-09-2000).]
 

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OBNXUS67

Is your torque converter new? I have experienced one out of balance before. If thats the case try unbolting it and pushing it back from the flexplate, then crank her up and see if there's a difference. Just a thought.
 

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Discussion Starter #6
Thanks for responding guys. The flexplate was not balance WITH the crank as a set. I'm pretty sure it was a cast crank and it was not balanced. Therefore, the balancer and the flexplate have to be balanced. Now, the new flexplate is a balanced type. So, now what guys. I really need help.

Tony

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obnoxious 67 camaro under construction. TH350/383 stroker w/ aluminum Eldlebroc RPM heads,cam, and carb.
 

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the 400 flywheel and ballancer have large honkin' weights on 'em. Make sure yours do. The ballancer weight is funny on the 400, If i remember correctly they have metal removed from the outside of the ballancer, instead of a weight on the inside cast into the hub like the 454 does. The 400 flex plate should have a large weight on the outside of the wheel, If I remember right , it has a few holes in iot and is different from the 454 flexplate. I'ts been a while since I have done a 383, but i was able to use new 400" flexplate and ballancer with only a negligable amount of shake. obviously a professional ballance will be your best bet.
Good luck
John
 

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Make sure you have the flexplate on correctly. The crank should have a locating
dowel pin and a corresponding hole in the flexplate. I built a 383 and had the same problem. The machine shop had left the dowel pin out of the crank and I accidently put the balanced flywheel 180 degrees out! Talk about a bad vibration.....just like what you are experincing.


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'69 SS 396/375hp L78 M21 3.73 Fathom green/medium green interior

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