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Discussion Starter #1
I loaded the car up with tool recommendations from VMF'ers on a previous post and headed beyond the limits of my subdivision for the first "Cruise". I was excited and nervous at the same time.

All was well until I hit 35 mph, then I noticed a vibration that seemed to resonate about the car. It got steadily worse until I got over 45 mph, when it started to even out and not be as evident. The vibration seemed to surge, and wasn't steady. It vibrated so much that you couldn't see out of the rear view mirror and the dash panel shook.

I've had out of balance tires before, but that seemed to be a constant vibration and didn't throb/surge like this did. There was no shimmy in the steering wheel, so I don't suspect tires.

Here's some possibilities I see and things I would eliminate:

I would say it's not:
1. Engine - vibration persists when car in neutral
2. Wheels - rear tires new and balanced and no steering wheel shimmy
3. Alignment - I had it aligned yesterday and watched as they did it.

But it could be:
1. Driveshaft - didn't mark it when it was taken off, plus mated to different rear housing. Could I have put it in facing the wrong way front to back?
2. Rear wheel bearings - When rebuilding rear housing, the weel bearings spun only about 1/2 turn, were tight, and no leaks so I presumed they were good.
3. Differential - it was my first rebuild (but no clunking or whining from it).
4. Transmission - I know nothing about it except that the oil looked fine when I changed it and the filter.

How would you try to start isolating this problem?

Thanks,
Glenn
 

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sounds like something in the rear end if it was in the front you would feel it in the steering wheel could also be bad u- joints. ::
 

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Did you put new u-joints in the driveshaft? I know this sounds crazy but somtimes taking the rear u-joint loose from the rear yoke and rotating it 180 degrees and reinstalling it will make a vibration go away or diminish significantly.
 

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Discussion Starter #4
Ahh, forgot to mention that I did put new u-joints on it. One did seem to be a little tighter (harder to move from side to side when installed) than the other.

It seems simple enough to rotate the shaft 180 degrees at the rear yoke, so I will try that first. If that doesn't help, then what?

Has anyone tried jacking the rear of their car up and looking for the vibration? Doesn't sound like a good idea unless in a empty parking lot or something though.....
 

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Where in Houston are you? I have a friend with a 67 and it is apart, maybe you could try his driveshaft to see if it is that simple.
 

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Put the rear of the vehicle on jackstands, and block the front wheels. Get a good friend to sit in the car, and have him take it up to speed, and watch the driveshaft to see if it gets fuzzy. You can even take a stick and hold it against the driveshaft to see if it bounces off. You should be able to hold it on pretty steady if things are okay. I have done this before on my mothers F-150. The u-joints felt tight, but the whole thing was out of whack. New joints and a re-balance fixed it right up.
 

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Make sure your wheels were 'center-balanced'. There is a special jig for this. I had a similar vibration a year ago and after going to the third shop to find the jig they rebalanced the wheels and no more problem.
 

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Word of warning here. If the vibration is in the drivetrain, you may very well not feel it with the car up on stands as you are not loading the drivetrain.

Same problem with mine, except from 75 to 85 mph. Put it on stands - no vibration. Back on the road - vibration.

The problem started when I changed the rear gears. I'm going to try getting the shaft balanced and see if it goes away. I indicated the driveshaft front, middle and back and have .015" maximum out of round so the only thing left is balance.
 

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Does the car vibrate when you are parked in neutral at certain rpm's? If it does and the vibration surges I would suspect the transmissionmount. I had a similar vibration a few years ago and although the 35 year old rubber mount looked fine it was the cause of this bad vibration.
 
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