ebluekeys

WOW, I had no idea all this was so critical. I thought the whole purpose of U-joints was to ALLOW the differences to be accomodated. But, I WILL do all this measuring and what not this weekend... I've been working late on a regular basis, and just have no energy left when I roll in at home around 8!!

As for those locating "nubs" on the axle perch, I wouldn't shim it to the point where the they were to separate... I may be a little crazy, but I'm not stupid. I'm an engineer, and I'm constantly wondering what mechanical system might fail - especially when I'm driving over 70Mph!! Like a pilot, if I'm driving fast, I'm always alert to what I'll do, and where I'll try to go if something lets loose...

and thanks for all the good info guys. Looks like I might lick this high speed vibration problem after all...

ebluekeys

AFter TWO years, I found the problem. I had one of the 40 year old engine mounts separate, so replaced them with caged Urethane mounts and the vibration got AT LEAST 50 percent better (less). This was the tipoff that it was the motor. I replaced the stock harmonic balancer with a "fluid damper" type gizmo, and the vibration has now COMPLETELY GONE AWAY. I wish someone would have suggested this two years ago!! If you know your wheels/rims are properly balanced, and you've done some engine work, I recommend you get one of these right off the bat and save yourself a lot of grief!!

valley firearms

Wow, cool that you reported back. It's amazing how a vibration can migrate from one end of the car to the other and make you think it's something that it's not.
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fast66

I remember you having these vibration issues from months ago, maybe even a year, Great that you have got it sorted. Do you have any info on the dampener you used? I need to replace my balancer anyway, and perhaps it wouldn't be a bad thing to go with.