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Old 04-18-2008, 10:50 AM
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driveshaft length, vibrations?

I have a '72 Scamp with all the running gear and suspension out of a '76 4 door dart. IIRC the wheelbase is exactly the same, but when installing the driveshaft I have to completely compress the output shaft seal with the slip yoke to get the diff side u joint in.

where exactly to I measure from when determining how much the yoke needs to stick out of the tailshaft? I've heard multiple people say that 3/4" is correct, but is that from the tailshaft or the seal?

top is where im at, is the red area on the bottom what I should be measuring at 3/4"?



please excuse my mad mspaint skills






The car has a fresh transmission, before and after the trans swap the car has a really bad harmonic vibration that fades in and out, above 45mph or so and increases with speed. is this most likely either the driveshaft or the wrong pinion angle? is there anything else it might be? (the car is a 318, and has a 360 converter with the weights chiseled off

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Old 04-18-2008, 11:00 AM
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The part you have colored in red should be 3/4 of a inch. In other words you measure from the seal to the yoke. Also this measurement should be at ride height. The reason for the 3/4 of a inch is so when driving and your rear suspension is working up and down that when the rear end comes up the front yoke on the drive shaft won't bottom out and bind or beat the seal out of your tranny.

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Old 04-18-2008, 12:10 PM
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Quote:
Originally Posted by streetpirate
and has a 360 converter with the weights chiseled off
Your problem may be in the converter ...
Also ... I have taken a driveshaft and rotated it 180 degrees 2 the transmission ( without removal ) , reinstalled it into the rear end and the vibration disappear or be greatly reduced ...

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Old 04-18-2008, 12:21 PM
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when i make or install a driveshaft, i put the yoke of the driveshaft all the way in. measure from the back of the u-joint hole to the closest point of the pinion yoke, minus 1/16". (i make sure the rearend is at ride height) never had too short of a driveshaft.
alot of people use alot of methods, this is what i prefer.
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Old 04-18-2008, 12:43 PM
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Quote:
Originally Posted by Deuce
Your problem may be in the converter ...
Also ... I have taken a driveshaft and rotated it 180 degrees 2 the transmission ( without removal ) , reinstalled it into the rear end and the vibration disappear or be greatly reduced ...

.
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Old 04-19-2008, 10:49 AM
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Drive shaft

I think you maybe confused as far as measurements in this case.... The measurement does not always mean a specific lenght from the shaft or the seal. It means the amount of free play or travel front to back without bottoming on the tailshaft drive.

Put the shaft into the car as you would be driving it. With a sharpe marker, mark the input shaft of the driveshaft where the end of the seal comes. Remove the shaft from the rear end yoke. Now, put the input shaft back into the trans and insert to the mark. Now shove the driveshaft up into the trans until it hits dead stop, make another mark with the sharpe on the driveshaft. Remove the shaft and measure between the marks you made. If it measures three quarters, then things look good on that end now replace the shaft to the car as if you were going top drive it.....Does the shaft now fall between the two marks you made.... As long as the front mark is not too far away from the seal the lenght is not too short. On the other hand if the second mark cannot be seen when reinstalled then you might be a tad to long. Use your own descretion.
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Old 04-19-2008, 10:54 AM
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You need to push the slip yoke in until it bottoms out, then pull it out 3/4". With all the combinations of tailhousings, output shafts, and differing length of slip yokes, it's the only way to be certain you'll have the proper amount of travel.
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Old 04-19-2008, 11:48 AM
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If you measure as instructed and have the shaft balanced at a driveline shop that particular issue should be solved..Some cars just do have a harmonic at some speeds so an application of lizard skin or something of that nature to the floor boards and trunk area can help kill the harmonic..

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