Vibrations

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matt030305

matt030305

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Hey FABO Tech, I just need some answers to what might be the issue to my driveline vibrations.

This has been a problem since I have purchased my 71 duster that was swapped with a 340 and 727TF. I get these vibrations at around 60+ MPH (it is not a wheel balance issue as I have gotten them balanced) I recently began my scavenger hunt to figure out the culprit.

Last week I put the car onto jack stands and jacked up the rear. Put it into drive and let it roll slowly. Come to find out my whole driveshaft is shaking up and down. Linked below is the video of this.



I started thinking that the driveshaft is too short (yoke is too far out for the bushing) but it seems to have enough splines grabbing (it is a 6 inch yoke that has 2 inches of no splines). I read from one member that about 1-1.5 inches of slippage is okay and won’t cause any vibrations. I’m taking my driveshaft to a driveline tech tomorrow to see if it is balanced properly.

A picture is attached below to show the measurements of the yoke. The green measurement is the measurement where the output shaft sticks out. So I measured the yoke to the end of the tail shaft housing. The red measurement is from the seal to the yoke. (Both are measured in inches)

There is also some play up and down in the tail shaft attachment point from the yoke shown in this video.

I know that there is a bushing that the yoke rides on by using the tranny fluid. And that’s what I’m leaning towards being the problem.

My question is…
Is the play because the yoke is out too much or is it from a worn bushing or is it both??

IMG_6064.jpeg
 
Your third picture, the centerline of the u-joint portion of the slip yoke does not appear to be inline with the shank of the slip yoke, to me, that slip yoke is twigged.
 
Max1196 said:
Your third picture, the centerline of the u-joint portion of the slip yoke does not appear to be inline with the shank of the slip yoke, to me, that slip yoke is twigged.
Click to expand...
Now that I’m looking at it, you’re right! I’ll be sure to let my driveline tech know.
 
Okay, I just looked at the yoke, it’s just the orientation of how I took the photo, it doesn’t appear to be bent.
 
Take the drive line to a drive line shop and have them “recondition” it. I.e. putting in new non serviceable u joints, a balance and a paint job. Last one I had done was 150 bucks total
 
Here is my take...

  1. Unless the slip yoke is particularly long the amount out of the trans is excessive.
  2. There appears to be excessive play in your transmission mount
  3. The video where you are raising the drive shaft up and down it looks like the U joint is moving.
  4. The wabble in the drive shaft looks a bit much
  5. I did not see any video of the rear u joint at the diff.
I would absolutely take the driveshaft to a shop and have them evaluate it. They will probably do it for free.

With the rear axel supporting the body weight, disconnect the rear u joint. Slide the drive shaft forward till it touches the transmission seal. Back it out 1 inch.


Measure from the center of the slip yoke to the center of the diff yoke.

See how that measurement compares to your driveshaft.

If it is more than 1/2 inch difference I would have a new drive shaft made.
 
Yes, 1" out from the tail shaft seal is more ideal.

The more that it is hanging out the more it can exaggerate any problems of wear.

☆☆☆☆☆
 
I was thinking that the play is from the bushing for the tail shaft housing where the yoke rides on.

I was also going to replace the transmission mount as well. Two birds one stone type of deal. More new parts more reassurance.

The driveshaft that is currently on it now is 44.5”. I did what Dana told me to do and I need my drive shaft to be 45” to be at the ideal 1” of slippage for the yoke.
 
Drive shaft looks too short to me. Not enough engagement in the bushing. That big seal at the back is just a dust seal. You can run just a standard seal instead of that one to allow more yoke to be inserted into the trans.
 
Is that a new U joint? Have you had the driveshaft out? Maybe it's just me but the caps of the u joint are sticking out? 1st video looks like bad u joint. My Blue dart sits in almost the same. I agree it should be around an inch but I have had no issues in ten years.
 
So the news is back. The driveshaft had a crooked weld and needs to be lengthened. My driveline guy is going to lengthen it by 3/4-1” along with replacing my u-joint.

He is making a new one for me and it’s going to cost me $400. Sucks that I have to spend that much money on something I won’t see but this is a once in a lifetime thing, won’t have to worry about it again.
 
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