My Car has developed a Vibration / Noise in the last 2 Weeks. Its a light Vibration with a "drumming" Noise that repeats louder/ lighter. The Vibration is through the Floor not Steering. I have checked Brakes for Drag and Tires for Separation ( Radials). I pulled the Driveshaft Today to make sure new U-Joints were not tight and rotate freely and balance Weights are in Place. Motor / Transmission  Mounts are new and Tight.  The Vibration/Noise is diminished if I shift to Neutral . The only change I made recently was new Standard Mufflers and some Pipe bending. Nothing is touching the Frame. Any Suggestions?

  

Not sure but dual exhaust at least on my '55 routes through openings in the frame.  I get a vibration/rattle on occasion, usually when backing up in my case, which I attribute to the exhaust knocking against the frame opening.   It's near the front seat, if I remember correctly.  Maybe if you have dual exhaust passing through the frame on your '56 you should grab it and shake it to see if it rattles against the frame.

Again, this is just an idea.  I could be all wrong.  And often am!!

Check your motor mounts/bushings for a broken mount or a cracked bushing.  The engine can move enough to cause the exhaust to touch and vibrate.  Sometimes it will actually sit back in place properly, and everything seems ok, but the engine torques over on start up and can cause your vibration.  Just a thought.  Joe-JDC

JDC

Motor Mounts and Transmission Mount new and Tight. There is clearance around the Pipes where they go through Frame. No Movement in the Exhaust at all with all Hangers in place and tight. Spinning the Wheels off the Ground I don't hear any Noise like bad Wheel Bearing.. Definitely seems to be from Front but not through Seat or Steering.Feel it through Feet on Floor. Strange. The Car I used to own still had the Heat Shields welded to the Floor above Mufflers. This One now does not. I don't know if that would be a Reason for the Noise/Vibration since I changed the Mufflers but it was not there initially after Exhaust Repair.Started a couple of Weeks later. 

  

Have you checked diff pinion and extension housing bushing for movement?
I feel for you trying to track vibrations down. 

The Diff is fine. Fordomatic. Should there be basically no Play where the Yoke goes into Transmission? This Vibration is happening when driving at steady speed like 40-55. Under Acceleration seems to disappear. 

  

How about the torque converter bolts? Also if you don't have the later complete circle flexplate the 4 point mounts sometimes will crack or break a mounting point.
 



Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Does it completely go away when shifting to neutral?  If not i am thing maybe wheel or axle bearing.  Make sure wheel lugs are tight. Just a thought 

Located in Harford County Maryland 

I chased a similar vibration for a long time going through everything, it finally turned out to be the bushing in the tail housing of the trans. It didn't feel that bad but I think it was from the pressure of the seal holding it somewhat. After removing the seal you feel the slop better. After replacing the bushing it cured 90% of the problem, still haven't found the other 10%.

Its been replaced with the new Style Illustrated. Previous Owner did it. I had the Engine apart this Winter out of the Car so I am sure its all good.