Drivetrain Vibration/Resonance

[rebootej]

Hi guys I've got a 74 Satelite Sebring, its been moded a bit. Has a rebuilt 318 and A518 (Transmission 727 with OD). It has a vibration/resonance that is RPM-related. It starts slow and low and as RPMs build, it gets faster and louder, especially over 3000 RPMs at highway speeds but once it shifts it's pretty much gone.
Any ideas where I can start? Since it drops at RPM I can know it is coming from the transmission or forward right? Any advice would be greatly appreciated.

 

[Mick56]

Does it vibrate if you are in neutral and raise the rpm's?

 

[rebootej]

You can sort of hear it in this video at the local drag strip. and see me get smoked by one of my high school students.

https://youtube.com/shorts/51yq7nJ5K6k?feature=share

 

[rebootej]

Does it vibrate if you are in neutral and raise the rpm's?

Yes it does

 

[Mick56]

Then it seems engine related. I would check the flex plate and converter bolts first.

 

[Slap Stick]

And the harmonic balancer. It may have separated.

 

[Dave6T4]

I had the same vibration in my 440 in my '67 R/T. It turned out to be my water pump. Grab your fan blade and see if you can wiggle it. If you can, the bearing is shot.

 

[rebootej]

Thanks, guys I'll check those out. How can you tell if the Harmonic balancer has shifted?

 

[Mick56]

You would need to find the TDC of the engine, and see if the mark on the balancer lines up with the 0 on the tab.

 

[rebootej]

You would need to find the TDC of the engine, and see if the mark on the balancer lines up with the 0 on the tab.

Sounds good Ill check that out. Thank you.