Pinion Angle/Tailshaft Bushing

Working on my 4 speed Dart with minor humming, grumbling vibration in 4th above 2000 rpm/55 mph. Still there when in neutral gliding but reduced. Can feel roughness when pushing clutch in at that speed. It is noticed in the float zone of the throttle while cruising only and from the trans forward. Can feel it in the shifter and even a bit in the steering wheel. 3.91 gears are in the rear and new 3” driveshaft was built to potentially help issue with new u joints, but it didn’t help. Tires are all good and balanced. There is some very minor side to side play of the slip yoke into the trans, so I am suspecting the tailshaft bushing has some wear (the trans needs a re-fresh anyways). Either than, the pinion angles, although look parallel, may not be perfect, causing this symptom.


Had a similar issue on another car of mine recently.


Being that this vibration/hum isn’t violent and shaking the car to pieces, and I am suspecting either the tailshaft bushing to be worn, or pinion angle to be off slightly, do you think the car should be fine operationally until I can get a chance to refresh the trans and get the pinion angles just perfect? The car is driven a few times a week, about 100 miles total over a week.