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304 / 904 ?
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mikesramblur View Drop Down
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mikesramblur Quote  Post ReplyReply Direct Link To This Post Topic: 304 / 904 ?
    Posted: Mar/11/2021 at 9:39am
I have a 258 with a 904 attached. Im swapping a 304 in and would like to use the 904. Is it a direct swap or will there be balancing problems? The 304 flywheel will not take the 904 converter, but the flywheel from the 258 fits perfect. Just not sure about the balancing.
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Points: 4866 		Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2021 at 10:01am
If the 304 is a 72 or newer, the crank flange will fit the 904 torque converter.

The 258 is internally balanced so it doesn't have balancing weights welded to the flexplate.

The 304 (and all AMC V8s) are externally balanced, also referred to as Detroit balance, so the 304 flexplate will have a balance weight welded  to it. Flywheels (for a manual transmission) will have a cast in place balance weight on them. The weight will be different amounts and in different spots depending on engine size.
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mikesramblur View Drop Down
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mikesramblur Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2021 at 10:26am
The 258 converter will fit into the 304 crankshaft but it wont fit the 304 flex plate. Bolt holes are all wrong. So do i use the 258 flex plate?
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Hurst390 View Drop Down
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Points: 5822 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2021 at 11:11am
No unless you have it balanced. Redrill the 304 plate
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mikesramblur View Drop Down
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mikesramblur Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2021 at 11:26am
Ah ok. Thanks
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Points: 3557 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2021 at 1:58pm
Check if the flex plate has one or two sets of converter mounting holes.
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mikesramblur View Drop Down
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mikesramblur Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2021 at 2:43pm
just one set.
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mikesramblur View Drop Down
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mikesramblur Quote  Post ReplyReply Direct Link To This Post Posted: Jul/21/2021 at 4:33pm
Ok back to this. Life gets in the way. The flexplate i thought was a 304 is actually a Th400 plate. Soooo, i guess i will have to get a 304 plate ?
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Points: 10356 		Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/21/2021 at 7:12pm
Just be careful as a lot of places will list flywheels & flex plates fitting all motors.
That is only half right, they will all bolt to the cranks of the different motors but ........
The weight / balance will be off and can hurt the motor over time.

At one time I think there was a thread on how to tell what flywheels & flex plates fit what motors by where the weights were?
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mikesramblur Quote  Post ReplyReply Direct Link To This Post Posted: Jul/21/2021 at 7:17pm
I noticed that today, that places are listing them to fit all motors. 
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