Please help me diagnose vibration 1966 289 4V :SOLVED!

[c9zx]

I'm glad you got it fixed. Chuck

 

[Seckc1]

Unfortunately, at this point I think you must find out if the flexplute is 28 or 50 oz. imbalance, somehow. If you confirm it is 28 oz. then all that remains is a bad convertor, bad balance, or worn/damaged pilot hole in the end of the crank. Hope for a bad convertor. I'm out of ideas. Perhaps someone thinks of something we've all missed so far. Chuck

 

[Seckc1]

I’m having the same issue. So if by part number I determine it has the 50 then I should replace it with a 28?

 

[Idaho Chris]

I’m having the same issue. So if by part number I determine it has the 50 then I should replace it with a 28?

Unless your engine was rebuilt or replaced with a later year 50 oz balance, and you have the same issue as me with an improperly installed 50oz flexplate, then swapping the plate for a 28oz is the only fix.

Good news though, you don't have to pull the transmission. With the coolant lines unhooked and the transmission crossmember unbolted you can slide the transmission back far enough to replace the flexplate.

 

[Seckc1]

Unless your engine was rebuilt or replaced with a later year 50 oz balance, and you have the same issue as me with an improperly installed 50oz flexplate, then swapping the plate for a 28oz is the only fix.

Good news though, you don't have to pull the transmission. With the coolant lines unhooked and the transmission crossmember unbolted you can slide the transmission back far enough to replace the flexplate.

Thanks now off to get a new flex plate

 

[clevelandcoupe]

Congrats on solving your vibration... I have been chasing one in my Mach 1 since I installed a 5 speed last spring. I need to get it on a lift to check mounts, etc.
Thanks, Jay

 

[mrgmhale]

It was when I was rereading this post from its inception that I paused long enough to recognize how much differently our AOD swap in place of the original C4 in our 73 Mach 1 could have gone. In our case the original 302 2v engine was replaced by the prior owner with a 351W built for moderate street/strip performance. We had no imbalance or other vibration. While preparing to order the various parts for the AOD swap I recognized the 28 oz vs 50 oz flex plate issue existed, and decided to usr the conversion kit from California Pony cars (PN TRA-650-421) which was for 289/302/351W to bolt to the AOD. The Flex Plate in their kit is the 28oz weighted unit. With other reading I determined that was the correct weight, but I was prepared mentally to pull the AOD and swap in a 50 oz Flex Plate if I noticed any vibration. The gods were smiling on me during the swap to the AOD tranny, no vibration. Whew...

https://calponycars.com/products/1965-1966-a-o-d-conversion-kit