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1970 390 flexplate

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Transmission & Drivetrain
Forum Description: If it's between the engine and wheels, it goes here
URL: https://theamcforum.com/forum/forum_posts.asp?TID=39339
Printed Date: Mar/28/2024 at 3:21am
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Topic: 1970 390 flexplate
Posted By: RedX
Subject: 1970 390 flexplate
Date Posted: May/05/2012 at 10:13am
poormansMachine posted a photo of a 70/390/Borg Warner flexplate on Jun/03/2008.   That photo has been moved or deleted and now I need to compare it to my flexplate.  Is there a way to retreive that photo?   My torque converter to flexplate nuts have come loose several times and i just replaced the nuts with new ones.   The stud holes in the flexplate have elongated (egged?).  Can I have the holes redrilled in a different location without affecting the balance?   Thanks.   This forum is female caninein'.  I have learn so much from it.  I' believe restoring an AMX would not be possible without the AMC Forum and e-Bay.   Thanks for any help you can provide.



Replies:
Posted By: 1970390amx
Date Posted: May/05/2012 at 11:25am
I dont see a problem with having the holes redrilled in a different location. As long as no weights are removed and nothing intefers with any weights.

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1970 390 4speed Bittersweet shadow mask AMX
1970 Amx missing most everything, or in a box


Posted By: FuzzFace2
Date Posted: May/05/2012 at 11:35am
^^^x2 what he said^^^
I would also use blue loctite on the nuts this time around.
Dave ----


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TSM = Technical Service Manual

75 Gremlin X v8 for sale
70 Javelin 360/auto drag car
70 Javelin 360/T5 Street car


Posted By: sidewinder
Date Posted: May/05/2012 at 11:38am
If the pics were posted from a remote host ( photobucket) and  they are deleted or moved from there they won't show up here on the forum.  I don't think the forum had the ability to host pictures in 2008.

Chuck Page


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Chuck Page ,AKA Sidewinder
1968 "BLACK CHERRY" Javelin
Previous owner of 2013 Heritage Cup winner 1970 BBO AMX




Posted By: amx39068
Date Posted: May/05/2012 at 5:19pm
Originally posted by 1970390amx 1970390amx wrote:

I dont see a problem with having the holes redrilled in a different location. As long as no weights are removed and nothing intefers with any weights.


This is incorrect. The offset weight is relative to the index of the bolt holes (one is off center from the other 5) so drilling the bolt holes in a different location will move the flex plate weight to an amount equal to the offset of the new holes and create an out of balance condition. The 6th bolt hole is offset specifically to ensure that the weigth on the flywheel is in one location only relative the counter weights on the crankshaft.

Will333 discovered his car had the wrong harmonic balancer offset weight on his 68 390 and it caused a vibration that was resolved by putting the correct balancer on his engine. The same would hold true if you move the bolt holes on the flex plate.

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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development


Posted By: whizkidder
Date 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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Ron Frost
marne1ancient @ gmail.com
910 nine two two 0563

"There is no limit to what a man can do, so long as he does not care a straw who gets credit for it. Charles Montague


Posted By: bbgjc
Date 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.


Posted By: 390spirit
Date 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!


Posted By: RedX
Date 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.


Posted By: amx39068
Date 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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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development


Posted By: 69amxr
Date 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?


Posted By: amx39068
Date Posted: May/07/2012 at 3:14pm
they are different

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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development


Posted By: 69amxr
Date 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.


Posted By: amx39068
Date 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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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development


Posted By: Rebel Machine
Date 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-
 



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