304 vs 360 flex plate

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   Hello,

I finished my new 360 build only to realize my donor 360 was in front of a 400t and balanced to the 400 flex plate.  My original 304 was in front of a 904 and that is the trans I will be using.  I still have both FPs.

They are both weighted but look very different.  I am not sure if the balance is the same.  

I looked up multiple years and part numbers via rock auto and it appears the only difference in flexplates was by the change in transmissions.  (example; a javelin calls for the same FP with a 304 or 360)

Can anyone with certainty say if 304 and 360 with the same trans use the came FP.  If not,  what is the difference.   I hate to trust aftermarket part numbers and my machine shop is backed up and i was hoping to get this motor in.

Thanks in advance,
Chris

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chris989 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Jun/04/2014 Location: boise Status: Offline Points: 63	Post Options Post Reply Quote chris989 Report Post Thanks(0) Quote Reply Topic: 304 vs 360 flex plate Posted: Jul/05/2017 at 2:41pm
	Hello, I finished my new 360 build only to realize my donor 360 was in front of a 400t and balanced to the 400 flex plate. My original 304 was in front of a 904 and that is the trans I will be using. I still have both FPs. They are both weighted but look very different. I am not sure if the balance is the same. I looked up multiple years and part numbers via rock auto and it appears the only difference in flexplates was by the change in transmissions. (example; a javelin calls for the same FP with a 304 or 360) Can anyone with certainty say if 304 and 360 with the same trans use the came FP. If not, what is the difference. I hate to trust aftermarket part numbers and my machine shop is backed up and i was hoping to get this motor in. Thanks in advance, Chris

304-dude Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082	Post Options Post Reply Quote 304-dude Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 3:04pm
	The only difference is the balance weight. To get a good idea, here is a link, the photos are about mid way down. http://theamcforum.com/forum/flex-plate-id_topic4832_page4.html
	71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker

chris989 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Jun/04/2014 Location: boise Status: Offline Points: 63	Post Options Post Reply Quote chris989 Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 4:00pm
	304 dude, I read through that post, I see the pics of the two flexpate comparison. The weight on my 304 plate looks more like the 360 in the pics. In the pics, the 304 looks thicker. Is it possible they weigh the same?

304-dude Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082	Post Options Post Reply Quote 304-dude Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 4:21pm
	No, they don't cannot be Interchanged, without effecting balance. When I took apart two 304 engines with their flexplates are installed. They both had the wide block type weight. The 360 weight if not long, may be in a different clock location on the flexplate. It is possible the engine has been put together with a transmission off 360. Best thing to verify is to locate the harmonic balancer 's part number located on the back side inner area. Then compare it to verify nothing else was swapped to the 304 that may make balance off.
	71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker

tufcj Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Supporter of TheAMCForum Joined: Jul/10/2007 Location: Watkins, CO Status: Offline Points: 4084	Post Options Post Reply Quote tufcj Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 4:21pm
	The 304 and 360 flexplates are physically the same but balanced different. Since AMC V-8s are externally balanced, the bigger pistons in the 360 weigh more, so the balance is different. You can use either the 304 or 360 flexplate, and have it "match balanced" to the TH400 flexplate that was balanced with your motor. You'll want to do that or have the entire rotating assembly re-balanced. Bob tufcj
	69 AMX 74 Javelin AMX 67 Rogue If you need a tool and don't buy it... you'll eventually pay for it... and not have it. Henry Ford

304-dude Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082	Post Options Post Reply Quote 304-dude Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 6:57pm
	Since I raised the question, here are the part numbers for the 304 harmonic damper and 360 to verify which one you have, in case it may have been swapped. 72 on up 304: #3216083 72 on up 360: #3230131 Below is a comparison of the weight locations. The white lines are the ends of the balancer weight protrusion. Seems like a lot of our pictures for comparisons are lost to Photobucket. I am sure there is some wrong doing going on, as holding photos they know are being used on sites and forums, and holding them for ransom so to speak. At least we got part numbers Inn text, else this site would be bare like Old Mother Hubbard's cupboards. Edited by 304-dude - Jul/05/2017 at 7:12pm
	71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker

purple72Gremlin Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Online Points: 16611	Post Options Post Reply Quote purple72Gremlin Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 9:01pm
	I can tell you from past experience that the flexplates do NOT interchange. And since the 360 had a TH400, it will also have a bushing in the crankshaft pilot hole, (Because the standard TH400 converter has a smaller hub than the TF converter does) remove the bushing so the TF converter will fit...............(You dont use a bushing for the TF) Edited by purple72Gremlin - Jul/05/2017 at 9:07pm

chris989 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Jun/04/2014 Location: boise Status: Offline Points: 63	Post Options Post Reply Quote chris989 Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 8:01am
	Thanks for the replies. I am confident I will need another FP. Where i can find the correct 360 FP that was in front of a Torque Flight. Will a FP from a 727 fit the 904? I have read mixed information about this. Can someone point me towards the right part. I spoke to a local guy from craigslist but i am not so confident with it. When i look up the part to order new, the 304and 360 are listed the same. Pioneer lists a FRA118 for an 85 360 wagoneer and my 80 304 CJ7 noting a 727. CJs never had a 727. They lists the FRA108 for a 904, I called pioneer and tech could not tell me the weighting Sorry, This is the first Chrysler auto i have ever had so i do not know much. I will order a new FP and take it to the shop to triple check.

304-dude Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082	Post Options Post Reply Quote 304-dude Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 8:43am
	I found an AMC 360 flexplate, that is a wee rusty, but usable on ebay. http://www.ebay.com/itm/AMC-AUTOMATIC-FLEXPLATE-FLYWHEEL-AMX-JAVELIN-JEEP-MATADOR-REBEL-MACHINE-390-360-/332262962229?hash=item4d5c6a7435:g:uXcAAOSwiONYM1KT Edited by 304-dude - Jul/06/2017 at 9:06am
	71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker

chris989 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Jun/04/2014 Location: boise Status: Offline Points: 63	Post Options Post Reply Quote chris989 Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 8:47am
	Dude, Can you tel from the photos if it is correct? In the Ebay description the seller does not know what it came off of I prefer to buy new if i can get the right part number.