Engine vibration

[Paul G]

As engine rpm rises, whether in nuetral in the driveway, or cruising down the road I am feeling a vibration in the floor of the car. The vibration starts about 2000 rpm and gets worse as rpm's rise. I feel I have elimated the drive line causing the vibration by bringing the car up to speed, over 60 mph, engine turning at 2500 rpm. Feeling the vibration at this speed and rpm I can put the trans in nuetral, rpm drop to idle, and the vibration is gone. The car is coasting with no vibration.

The engine is a 72 360. This should be an externally balanced engine right? Because it vibrates at higher rpm, I put a new Summit brand vibration damper on it. The new damper is weighted (and has timing advance marks on it). It made no change in the vibration. So that was eleiminated.

Torque converter is next. It is a Hughes lock up converter nuetral balanced, using a B&M flex plate with a half moon shape cut in it for balancing. Could the converter be causing the out of balance? Can a converter go bad and get out of balance?   

Could this engine have been built with an internal balance? Using the proper for the year external balanced damper and converter causing the vibration?

I ask because I have been eleiminating vibration issues one at a time for a long time with this car. This is about the end of it I hope.

[flyinlow]

 Take off all the fan belts and run the engine (short time only) this will eliminate an accessory problem. Any change?

I had an aftermarket alternator cause problems once.

[cdr]

Take off all the fan belts and run the engine (short time only) this will eliminate an accessory problem. Any change?

I had an aftermarket alternator cause problems once.

Yes, & I have also had a fan blade that was bad.

[Paul G]

I will try backing off the fan belts.

[Paul G]

Havent backed off the belts yet, but did take a look under the car. Found a broken trans mount. Replaced it and the engine is smooth now till around 3500 rpm before i start to feel it in the floor.

[Paul G]

I wondrer if the whole drive train is not in a bind?

[flyinlow]

Do you have a GoPro camera? Mount it under the car see if you can film the vibration? It is a way to see what the engine or drivetrain is doing under load.

If you think it is the converter out of balance , you could put a weight (washers) on one converter bolt at a time and see if it changes things.

A drivetrain issue would not normally effect the car in neutral and you stated the vibration was present in neutral/park.  Engine, accessories , flex plate , converter and transmission pump are what is spinning.

Take the belts off and run the engine without the alternator, PS pump, water pump, and AC spinning . A short 30 second run would not overheat the engine.

[Sublime/Sixpack]

Have you always had this vibration with your current engine and trans.?

[Paul G]

Have you always had this vibration with your current engine and trans.?

Short answer is yes.

[Sublime/Sixpack]

I suggest like already mentioned, take the alternator belt off and run the engine. Through the years I've had two alternators that caused more vibration then one would expect.
And for what it's worth three years ago I pulled the 318 out of my '68 Coronet (kept the original A904 Trans.) and installed a rebuilt 360 engine that I had used for 41,000 miles in another car without any vibrations. I used a rebuilt torque converter with the added weight for the 360. I then had a vibration. Checked angles, had the driveline straightened and balanced. Still had the vibration. It seemed that it was in the floor board so I assumed it was driveline related. Turned out it wasn't. Even in neutral I had a vibration that started around 3000 RPM and got worse. A year later the A904 went bad so I replaced it with a rebuilt A904 with the same weighted torque converter. Still had the vibration.
Fast forward to September 2017, I picked up a A999 rebuilt trans. with rebuilt torque converter. Vibration is gone! My conclusion is the T.C. for the 360 was defective or became defective if that is possible.
I'm not saying this is your problem, just offering my input based on my own experience.
Good luck!