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1970 390 flexplate

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Rebel Machine View Drop Down
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    Posted: May/09/2012 at 8:46pm
Originally posted by 69amxr 69amxr wrote:

One more question along this same line.  Is the flex plate from a '69/390 the same as the flex plate for a '70 390?  are they interchangeable?
 
 
Originally posted by amx39068 amx39068 wrote:

they are different
 
Are they? The flexplate from my '70 Machine looks the same as the one from my '69 AMX.
 
-Steve-
 


Edited by Rebel Machine - May/09/2012 at 8:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2012 at 4:09pm
I had two 68/69 service replacement blocksm one NOS and one used, and both had the correct 68/69 deck height, were balanced correct for the 68/69 model year and had the correct pistons, rods and crankshaft for 68/69. The 70 service replacement block was a different block and used the taller block for all ther 70 390 and 401s but should have the correct internals for whatever years it replaced.

What may be your case however is that someone unknowingly used a later service replacement block that was not correct for your year at some time in the car's life and swapped the earlier balancer and flex plate without realizing they are different than the ones that go with the earlier engines. For all you know, you could have a 401 lurking under the hood and the only way to tell is to pull it out and drop the pan to see what crankshaft and rods are actually in the block.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69amxr Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2012 at 3:22pm
thanks for the confirmation.  I am assuming they are balanced differently.  My AMX has a 1970 service replacement engine and I am guessing they used the original 1969 flex plate as I have a noticable vibration at highway speeds.  I have narrowed the source down to the trans or flex plate.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2012 at 3:14pm
they are different
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69amxr Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2012 at 3:07pm
One more question along this same line.  Is the flex plate from a '69/390 the same as the flex plate for a '70 390?  are they interchangeable?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2012 at 10:35pm
Originally posted by whizkidder whizkidder wrote:

I don't think he's changing the orientation of the plate to the crank -- he's changing the orientation of the converter to the plate. If the converter is neutral balanced it shouldn't matter.


Upon rereading the OPs original posting, I stand corrected but I would imagine getting the stud holes properly lined up so the converter is positioned perfectly from center will be a real PITA plus you would wan to drill the new stud holes equidistant from the old ones in either direction so as to not cause any extra stress points that might crack if the new holes are too close to the old holes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RedX Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2012 at 10:25pm
Thanks everyone.   I thought drilling was possible.   Didn't think about welding.   Could use a copper or brass 3/8" rod  to protect the "good part" of the hole during the welding process.   I installed the new nuts with the blue loctite.    Will try that first before pulling tranny.   Wish me luck.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 390spirit Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2012 at 7:25am
i took a F/P that was intended to be used with a 727 and drilled holes to make a TH400 converter fit it and mounted it to my 70 390 and it has worked great for 2 years now.

Yes it can be done!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bbgjc Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2012 at 6:52am
You could also weld the elongated part closed. A little welding wire, a little grinding and you're done. Probably quicker than drilling new holes, which would have to be correctly/exactly spaced or the flex plate will be out of true and will cause all kinds of issues.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote whizkidder Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2012 at 8:54pm
I don't think he's changing the orientation of the plate to the crank -- he's changing the orientation of the converter to the plate. If the converter is neutral balanced it shouldn't matter.
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