1955 Chevy BelAir

It is a great looking car.  Orange over cream - almost like a Dreamsicle.  Yet it has an annoying "thrumming" sound at speed.  Many thing had been done.  New tires, balanced and re-balanced.  A new driveshaft, different differential, different axles.  And yet all the time a continuous beat frequency at freeway speeds.  It is pronounced and felt in the seat of your pants while driving and disappears the second you ease up on the gas.

Going over every detail I pretended I had just bought the car and was trying to solve the issue for the first time.  Double checked the driveshaft spline and balance - all seemed good here.  Pulled the rear end apart and checked the gears, bearings and axles.  Pattern looked good, bearings felt fine and the housing wasn't bent.  I did notice the pinion angle wasn't where I'd like.  I double checked with Inland Empire Driveline.  http://www.iedls.com/Education-Zone.asp  I had seen a presentation at the Hot Rod and Restoration trade show so I knew they had the driveshaft details.

I even added new motor mounts since the previous 1955 setup originally included a bellhousing mount that had been removed when the TH400 had been installed.

Transmission investigation is next.  Stay tuned.