I have a 73 f100 with blown up 390 c-6. I'm putting in a 68 390 that was a four speed back and will be setting it up into the old c-6. The 68 4 speed 390 has a tiny harmonic dampner, the 73 390 c-6 has a big dampner do i need to put the big dampner on the 68 390 or leave the little one one and not worry?. Figure this issue and then it will be go time. Please help thank you.

 

I believe that if you are gonna swap the flex plate for the fly wheel you need to change the balancers too. In other words keep the manual balancer with the fly wheel and the auto (c-6) balancer with the flex plate. This should keep the engines balanced. Someone will chime in soon to let you know for sure. -Ed

 

There is no such thing as a manual (harmonic) balancer.

The A/T flexplate is the same for all 1965/76 352/360/390 engines.

C3AZ6312E .. Harmonic Balancer / Fits: 1965/67 F100/350 352 / Passenger Cars: 1958/59 332 / 1958/67 352 / 1961/67 390 / 1966/67 410 & 428.

D2TZ6316A .. Harmonic Balancer / Fits: 1968/76 F100/350 360/390 / 1968/71 Galaxie/LTD 390/428 (except 428 S/CJ).

C5AZ6375D .. FE Flexplate

Fits: 1965/67 F100/350 352 w/MX Cruise-O-Matic and 1968/76 F100/350 360/390 C6 // 1965/67 Galaxie/LTD 352/390 MX Cruise-O-Matic / 1966/71 Galaxie/LTD 390 C6 / 1968 427 C6.