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125 Posts
Discussion Starter · #1 ·
The hits just keep on coming...

‘67 K-code, 4-speed top loader, 3.89 rear gear, new to stock spec. drive shaft, new u-joints. Motor & trans rebuilt, rear only inspected for obvious defects/failures (none found) and re-assembled. 420 miles since assembled and back on the road.

Now that I have a bit more confidence in the motor I decided to start testing above 3500 RPM, what I found was a pretty nasty vibration comes in above that, but only in 4th gear (somewhere around 75mph). I feel it mostly in the seat and toward the center, i.e. not more to the left or right, and while under power. Hard to describe in words what the actual vibration is like but it comes on consistently and doesn’t seem to change much in frequency or intensity but then again, I'm not trying to push any limits just yet. It's like the drive line hits a point of resonance if that makes sense.

I rounded up what I think are all the usual suspects:

  • No vibration in neutral.
  • Changed to a different set of tires/rims, no change.
  • Pushed and pulled on each of the rear tires to detect any free play in the wheel bearings, none was detected.
  • Pushed and pulled on the pumpkin yoke, no free play detected there or the u-joint.
  • Pushed and pulled on the transmission yoke and found some lateral movement (up/down, side/side) there, the u-joint seemed tight but you can see the yoke moving where it enters the tail shaft.

At this point I need to ask, how much lateral movement of the trans yoke is too much (or too little)? Should there be some, none, somewhere in between?

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