I have a 73 f100 with a gernaded 390 and a Auto trans. The new motor I have installed is out of a 68 f250 with a 4 speed but hooking up to the c-6. The deal is the 73 with the auto trans has a big heavy harmonic balancer and the 68 with the manual has a tiny harmonic balancer. Does going from a manual trans to a auto require the bigger balancer or is it just year to year for the crank? I would like to fire the motor but worried about the balancer issue. Thanks for help.

 

I would tend to think it is a motor thing. Unless you are talking about the flywheel. Ford had a lot of variations. And as long as you are not changing parts you should be ok. But someone is going to correct me if I am wrong.

 

The differences could be related to the imbalance. You must have put the flexplate off your old motor on the new one. So just verify that the 2 motors have the same imbalance and you should be ok. I'd still keep the flexplate and balancer in matching sets. I'm personally paranoid about mixing them.

 

thanks for the advice. so I'm thinking the flexplate and harmonic balancer off old motor should go on new motor.

 

Something smells and it ain't hay.

D2TZ6316A .. Harmonic Balancer / Obsolete

Fits: 1968/76 F100/350 360/390 A/T and M/T // 1968/71 Galaxie/LTD 390 A/T and M/T.

Fits: 1968/70 428 Passenger Cars/Police Cruisers except S/CJ.
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C3AZ6312E .. Harmonic Balancer / Obsolete/Reproduced

Fits: 1965/67 F100/350 352 A/T and M/T / 1960/67 Galaxie/LTD 352/390 A/T & M/T (except 390 HiPo).

Fits: 1961/67 Thunderbird 390 / 1966/67 Fairlane/Mustang/Cougar 390 A/T & M/T.

Fits: 1966/67 410 Mercury Parklane // 1966/67 428 Galaxie/LTD A/T & M/T // 1966/67 428 Thunderbird.
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C5AZ6375D .. A/T Flexplate is the same: 1965/67 F100/350 352 C-O-M // 1968/76 F100/350 360/390 C6 // 1965/71 Galaxie/LTD 352/390 C-O-M/C6.

My guess is...with that 'tiny' balancer, that so called 1968 FE engine is actually a 352 from a 1967 or earlier Passenger Car or F100/350.

And...the only difference between the 1965/76 FE M/T flywheel for a 352/360 as opposed to a 390 is:

C5AZ6375K .. M/T Flywheel = 352/360 / Marked: C5AE-6380-J / (6) 5/16" pressure plate attaching holes on 12 3/8" bolt circle ~ Use with 11" clutch.

C5AZ6375L .. M/T Flywheel = 390 / Marked: C5AE-6380-K / (6) 5/16" pressure plate attaching holes on a 12 7/8" bolt circle ~ Use with 11 1/2" clutch.

One can be used in place of the other without any problems whatsoever. These same two flywheels were also used on 1965/71 352/390 Galaxie/LTD's.

btw: This is prolly the 200th time I've typed this same 352/390 harmonic balancer/flywheel/flexplate info here on FTE.

 

So to be a hundred percent, just bolt the motor to the c6 with the flexplate off the old 73 390 motor and leave the little balancer on there?