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By 55vickey - 12 Years Ago
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I'm getting a vibration in the car, 2500 rpm range, maybe around 60mph and up. 55 Victoria, 272, Mustang 3 spd, stock rear end 3.30. Been reading some articles on bad harmonics at a certain rpm range, and I'm getting close to that (2800), at 55 the car is ultra smooth, but 60+ and it gets very noticeable. Wheels and driveshaft have been checked for balance, spot on. My engine builder had me check for vibration in neutral, up to 3500 very smooth, does that rule out the harmonics issue, I'd like to have this solved before it gets put away for the winter. Thanx, Gary
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By gekko13 - 12 Years Ago
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Although you don't say, is this a recent occurrence? The wheels may be balanced but are they round? Tires can develop problems resulting in radial run out for example. That's pretty easy and cheap to check. Turn each wheel by hand and measure or observe radial or lateral anomalies. Have you tried to run it up to say, 70 mph then kick it into neutral and coast? That might give a clue as to where to look. Any unusual sounds associated with the vibration? Kind of grasping at straws here- so many possible sources.
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By Ted - 12 Years Ago
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Have you checked for looseness at the rear transmission yoke? A worn bushing in the transmission tail shaft and/or a worn yoke can cause some out of balance in the drive train.
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By MoonShadow - 12 Years Ago
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Did this start after recent transmission or engine work. If you had the driveshaft out try disconnecting it and rotating it 180 degrees and re-install. I've had a problem a couple of times in my years that this has fixed. My shaft guy says its like they are out of phase. He didn't know why it happens but it can show up on a brand new perfectly balanced shaft. Hope this helps. CHuck
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By Meandean - 12 Years Ago
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Had a 57 Custom that developed a vibration. Checked everything including the U-joints. Kept driving it and the vibration got worse and louder. It WAS the U-joint, but would lock in place when checking originally and only because it was so bad you could see the offset was it determined to be that. It was really hogged out, so it would seem to be easy to find, but was checked several times without identifying it.
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By bn - 12 Years Ago
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The output of a U-joint (when operating an an angle) will have an RPM which increases and then decreases with respect to the input for each revolution. This causes a vibration frequency of 2 x RPM of the drive shaft. For a drive shaft with a U-joint on each end and out-of-phase with each other, this rotational unbalance will be absorbed by torsional deflection in the drive shaft tube. If they are in-phase, the rotational unbalance will be additive and you will feel it as a vibration at 2 x engine speed (when in 1:1 high gear). At 2800 engine RPM, this would be 5600 cycles/Min or 93 cycles/Sec. There would be some vibration at any engine speed, but the reason you feel it most at 2800 RPM is because it is in resonance (matches the natural frequency) of something else in the vehicle. Most other vibrations in a vehicle occur at 1 x engine speed or at wheel speed.
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By MoonShadow - 12 Years Ago
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Very good explanation of the phaze but what about the 180degree rotation that helps with vibrations? I suppose manufacturing variations in the joints and couplers could account for it. Chuck
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By bn - 12 Years Ago
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Sorry, I should have worded it more clearly. The two U-joints being rotated 180 Deg from each other is what I was referring to when I said, "For a drive shaft with a U-joint on each end and out-of-phase with each other, this rotational unbalance will be absorbed by torsional deflection in the drive shaft tube."
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By MoonShadow - 12 Years Ago
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I understood what you were saying. Its a different question. For example, I had a new drive shaft made for my Dodge van. When I first drove it it had a cyclic vibration almost all the time. I went back to the shop and they checked the shaft. The balance was dead on so the guy put it back in rotated 180 degrees from the previous installation. He had marked the carrier and shaft when we took them out. The vibration was gone! Thats what I was wondering about. Apparently this is common enough that the shop was familiar with it but couldn't explain why. Chuck
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By Ted - 12 Years Ago
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55vickey (9/30/2013)
..... 55 Victoria, 272, Mustang 3 spd, stock rear end 3.30. .....Was the driveshaft modified for that three speed conversion? If so, then insure that the U-Joints were clocked or aligned with each other when any welding was performed. The balance of the shaft is yet another consideration.
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By bn - 12 Years Ago
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Allow me to try again. When the two U-joints are clocked properly (phased 180 Deg), for a given 1/2 revolution, one is increasing in RPM and the other is decreasing in RPM. Thus the vibration is cancelled out within the drive shaft tube. This is happening every 1/2 revolution, which results in a 2 x drive shaft RPM vibration. If the two U-joints are in phase with each other, the cyclic RPM is additive and is transferred into the rear end and the back of the transmission.
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By 55vickey - 12 Years Ago
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Rotated the driveshaft 180 degrees, no change, 65 70, put it in neutral, still vibrates. The drive shaft is relatively new, built for the tranny conversion. Before I got my suspension adjusted the driveshaft hit the floorboard a couple times, no dent in anything, just paint rubbed off? All fixed on that end. How much up and down or side to side play is allowable in the pinion yoke and tranny tail shaft? Tomorrow it gets put away for the winter, then I'll check tires for roundness, etc. Does the fact that its so smooth at 55 rule out anything? Thanks for all the suggestions, Gary
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By bn - 12 Years Ago
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Garry, I don't think rotating the driveshaft 180 Deg would have changed anything. This is a pretty complex subject and I think I may have miscommunicated by implying that the two U-Joints should be 180 Deg out of phase. In fact, they should be in-phase. In-phase would be established by rotating the transmission and rear end yokes so that they are parallel with each other (while the driveshaft is out of the car). For example, positioning the front and rear yokes so that they are both in the vertical plane and then installing the driveshaft (without rotating either yoke) would achieve the "In-Phase" condition. Also, it is very important that the front and rear operating angels are near equal. Here is a link I found on the subject: http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php
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By MoonShadow - 12 Years Ago
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I think the phazing of the drive shaft joints is a different, although related, subject. I do know that I have had two experiences with vibration in the drive shaft that was reduced by rotating the drive shaft at the rear end by 180 degrees. The people that I have had build shafts, a very old company, are the ones that first told me to try this. It helped. Chuck
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By The Master Cylinder - 12 Years Ago
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Chuck, I have done the same thing, rotated the drive shaft 180° and reinstalled. Vibration gone. For the life of me I can't explain it or anyone else who has done it can. Usually one of the first thing we try. Just one of those FM's, I guess.
I do know the trick has been around awhile because some old Dudes (older than me... ) told me about it!!
Edit; Off topic, I just mistakenly found out if you type : ) without the space between them you get 
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By John Mummert - 12 Years Ago
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My experience with driveshaft problems is limited but I have found a couple of things. First, if I put the vehicle in reverse and back up under load and hear a "ping", I know there is a bad U-joint. they seem to bind up in a forward direction and applying power in reverse breaks them loose. At this point if the u-joint is greased it will fail immediately. Done this one twice.As Ted mentioned, the bushing in the tailshaft causes many vibration problems. These can be identified by driving 60-70 MPH and varying the throttle. A bad bushing will not vibrate under load but when you let off the throttle it begins to vibrate.
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By ian57tbird - 12 Years Ago
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I had a similar vibration as John M mentioned but with the differential pinion. Power on = no vibration, power off = no vibration, but cruising it would vibrate.
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