Vibration at 2500-2800rpm

[mduenas]

I have had vibration since putting a rebuilt 302 in my truck. At the time I put a rebuilt Dana 20, 700r4 and new driveshafts. So I thought it was my driveline. I finally drove without the rear driveshaft and vibration is still there. Under load in the highway between 60-70mph it seems very harmonic. It is like driving over a rumble strip with a pattern.

I recently rebuilt the transmission, replaced my head gasket and replaced my motor mounts. Vibration is still there. I don’t know why I hadn’t, but I finally put the truck in neutral and revved it to the trouble some rpm band. The vibration is very much there, although not harmonic, but constant.

What could this possibly be? Imbalanced crankshaft? Harmonic Balancer?

 

[m_m70]

I had a similar issue. Have you tried pulling the belts off and see if the vibration goes away?? My issue turned out to be my fan of all things . Just remember that with your belts off things can get hot pretty quick so keep an I on that.
Good luck.....vibrations can be a tough diagnosis.

 

[mduenas]

I had a similar issue. Have you tried pulling the belts off and see if the vibration goes away?? My issue turned out to be my fan of all things . Just remember that with your belts off things can get hot pretty quick so keep an I on that.
Good luck.....vibrations can be a tough diagnosis.

I haven’t tried with no belts. But I’m on my 5th fan… so I can rule the fan out.

I’ll try to pull all belts. Rather that then tear down the motor again.

 

[Timmy390]

You say "a rebuilt 302". Does that mean not the original motor rebuilt? If it's not the original, what year is it? Think it was mid 1981 Ford went to 50oz in-balance

Tim

 

[mduenas]

Not the original, I got it with a destroyed 351 and out a 302 that had been newly rebuilt in it because of my Financial limitations at the time. From what I recall it is a 78. I should look again

 

[bmc69]

Tim posted what I was thinking....a 28 oz early flywheel is going to make a '81-up engine vibrate like you described.