Feel a vibration from Motor. I Think

[RangerRat]

The  390 in my 72' F100 has developed a vibration about 1600-1700 RPM. Then goes away by 1800 RPM. It's just in that couple hundred rpm. Can't feel it driving down the road. But very noticeable when parked if you idle it up or if fast idle is on. Harmonic balancer maybe?

[WConley]

I doubt it's the damper, since on a 390 they are neutrally balanced.  I'd check the cooling fan for looseness, or possibly a bent blade.  That seems like about the right rpm for a big heavy clutch fan to act up.  If you pull off the belts, and the vibration goes away, it's a good clue.

Another possibility is the torque converter throwing a balance tab.  Let's hope it's not that!

[RangerRat]

I looked over the damper it looks fine. No sign of the rubber part separating. That's a good idea about the belts. I'm going to try that today. I thought about the converter. I sure hope it's not that.

[machoneman]

Spin that fan blade over by hand and see how it goes. Should only spin at the max 1/2-3/4 rotation before stopping. Then, grab two blades and see if there is a lot of fore/aft play. I've also (some work here) taken off a clutch fan and run a cold engine for awhile to see if either noise or vibrations go away.

[RangerRat]

So I took the belts off this morning and sure enough no vibration. Great suggestion I would have never thought to try that. I swapped the fan clutch for an extra I had and the vibration is pretty much gone. The only thing I feel now is I believe just the exhaust pulses at a certain rpm. Before it would vibrate the steering wheel. No more. Thanks guys, I knew I came to the right place

[WConley]

   Glad it was the easy end of the engine.  Enjoy that great truck!

- Bill