My F150 has a 390 (FE) engine and it vibrates at 1100 RPM and above. At first I thought it was missing however removing the spark plug wires one at a time shows that all cylinders are hitting. The vacuum is steady at around 19, drops when cracking the throttle and goes up to around 22 when released. The exhaust sounds good (it has dual glass packs). The engine has good power. The carburetor is a 4 barrel Edlebrock, I switched to a Holly with no change, there is no smoke coming from the tail pipes.

The vibration does not change with the clutch pushed in so could it be a flywheel or pressure plate issue. The clutch operation is smooth, it does not appear that the flywheel is loose, prying back and forth does not show any movement. There are no knocking sounds.
This is a junk yard special truck so I have no idea what year the engine is. Did all FE engines use the same flywheel and crank pulley? Could it have the wrong ones installed?
Any suggestions would be appreciated.

 

you probably got the wrong flywheel, better pull it out and match it up to one for your engine and see where the weights are at.

 

I agree to a point .. The 390 is internally balanced .. The 70's 460s are internally balanced also and the flywheels are interchangeable .. Since it is a junk yard motor my guess is a externally balanced 460 flywheel was put on by mistake .. If that is verified as being the case you'll want that resolved ASAP or you will seriously damage the mains if you haven't already..

 

My best "guess" is wrong flywheel....

Flywheel (Manual Transmission) | Mustang 428 Cobra Jet Registry

 

Thanks for the information. Is there a way to identify the flywheel prior to removal to verify that it is the wrong one?

 

I'm pretty sure the part number is on the engine side, so no.

 

The 390 flywheel is exactly 1/2 inch thinner than the 460 externally balanced flywheel because of the counterweight. I don't have a 390 flywheel here to measure thickness for your base number but maybe someone else does ..

That being said the 390 bell housing would not work with the externally balanced 460 flywheel ..

 

Will a 460 bellhousing fit on an FE motor?

 

Look at the harmonic balancer: At the factory, a rubber gasket is placed between the inner damper and outer pulley, then the 3 parts are pressed together forming a one piece assembly.

Over time, the gasket age cracks/shrinks, causing the other pulley to "walk away" from the inner damper...causing a vibration.

If not noticed in time, pulley will separate from the damper taking assorted belts along with it...may end up in the radiator core. Not pleasant!

Same harmonic balancer: 1968/76 F100/350 360/390 & 1968/71 390 Passenger Cars // 1961/67 352/390 is different.
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1965/71 Galaxie/LTD 352/390; 1965/76 F100/350 352/360/390: The ONLY difference in the 2 flywheels used in these vehicles is: The bolt pattern for the pressure plate.

C5AZ-6375-K .. 352/360 Flywheel-184T ring gear / Use with 11" clutch / (6) 5/16" -18 pressure plate attaching holes on a 12 3/8" bolt circle.

C5AZ-6375-L .. 390 Flywheel-184T ring gear / Use with 11 1/2" clutch / (6) 5/16" -18 pressure plate attaching holes on a 12 7/8" bolt circle.

As long as you use the correct sized clutch, you can use the 352/360 flywheel in a 390, use the 390 flywheel in a 352/360.
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No such thing as a 460 flywheel or bellhousing until 1983 as this was the first year the 460 was available w/a M/T (and 4WD). 1983/97 460's came w/a hydraulic clutch.

ALL 1968/82 460's came with C6's / D7TZ-6384-A .. Flywheel Ring Gear-180T = 1977/82 351M/400 & 1983/97 460.
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D1SZ-6375-A .. Flexplate: 1968/73 429; 1968/78 460; SOME 1979 460's with block casting number D1VE-6015-AB.

D9TZ-6375-B .. 460 Flexplate-Use with block casting number D9TE-6015-AB / SOME 1979 460's; 1980/97 460's.

FoMoCo changed the 460 MID-YEAR 1979, has a weighted spacer. There are no before/from serial numbers/production dates, because this was a "running" change.