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Mysterious drive shaft vibration

28K views 11 replies 8 participants last post by  plinker17722 
#1 · (Edited)
Time for some clever problem-solving everyone.



I've got what I believe to be a driveshaft vibration. Primarily it happens under acceleration at 10 to 15 mph and 30 to 35 miles an hour.



I think I began to notice it after my muffler system was replaced, about six months ago.



Not wanting to remachine the driveshaft I decided to replace the front & rear flex disk and center bearing. Even though the old disks looked okay I had the parts around so I decided to swap them. That didn't work out so well. Within a few weeks of the swap the front desk was almost completely shredded. I decided to replace the front with a Lemforder disk to see if that would solve the problem.



It didn't solve the problem.



So I decided to bite the bullet and have my mechanic pull the driveshaft. He sent it off to North Carolina to be rebalanced and aligned. He put it back in and also replace the rear flex disk with a Lemforder, which had also begun to shred.



And guess what, it didn't solve the problem.



And here's a really strange part. The vibration still happens at exactly the same speed & under the same conditions as always, however it's now quieter.





///stumped\\\
 
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#3 ·
Vibration can come from a variety of sources. Even though you've likely checked some of them, check again.

Tires - very common and easy to not get balanced properly
Axles - they can get out of balance and feel like drive shaft
Fan - a bad bearing can throw the fan off center and create bad vibration
Transmission - not likely and hard to check, but certainly possible. Maybe rear bearing.
Center bearing - can go bad even if relatively new

All that said, I think you've got something else going on that's shredding your disks. I believe mine are original and have 230k miles on them. Even the cheap chinese ones should last for awhile. The only thing I can think of that would shred disks like that is alignment. Is it possible your rear transmission mount has collapsed or somehow been mounted off center? Or possibly the rear end shifted somehow? The flex disks are only good for a degree or two of misalignment.
 
#8 ·
Good ideas - let me try to respond to fine tune what's going on.

Tires - very common and easy to not get balanced properly
Axles - they can get out of balance and feel like drive shaft
Fan - a bad bearing can throw the fan off center and create bad vibration
Transmission - not likely and hard to check, but certainly possible. Maybe rear bearing.
Center bearing - can go bad even if relatively new
Tires are new and balanced
alignment is great
center-bearing - I'm not sure if it was rechecked when the driveshaft was reinstalled, but I'm pretty sure they did.
Fan - I've checked this by removing the fan and fan clutch and the vibration happens regardless.
Axles - never checked.

Never seen anything like this. I am assuming your center bearing is checked and OK. Also check the pilot bearings in each end of the drive shaft. I would also do a run out check on both the transmission flange and the diff flange.
Pilot bearing was replaced with the new drive shaft last week
What's a run out check on the flanges?

My first thought was trans mount. Check engine mounts too.
I just checked the trans mount and it's good. How precise does the placement of the trans mount have to be? Mine has a groove in it to be adjusted foreword and aft.

It's got to be something putting other than torsional stress on the disks. I like the pilot bearing idea. If they were shot, or gone, it would definitely create a tearing, off center vibration.
Iknow the front bearing was replaced then the shaft was reinstalled, not sure about the back.

Also the universal joint was replaced with the shaft.

keep it coming!!
 
#10 ·
You aren't too far from me and I'm parting a 51,000 mile 1972 350 4.5. It runs and I have to assume the transmission and drive shaft aren't in too bad of shape. It's being parted due to rust.
Fonz - Thanks for the offer... where are you?
The problem is that >in theory< the drive shaft and trans mount should be perfect... don't know that replacing it with an unknown quantity is going to solve it...

this has got me stumped. Tonight i'm going to put it up on a lift and see if i can get a look at the center bearing and trans mount.
 
#12 ·
These shafts hava a special angle to run at . You should find out how to check the angle from the work shop manual . Also if the rear sub frame is loose in any way [mountings worn] then the angle will be out making it wear the shaft mountings. I hope its a simple fix like just the wrong rubber doughnut thats been fitted .And even the doughnuts are fitted a cirtain way .Even the bolt are incerted one way .There is a right way to fit them and a wrong way . You have to fit front transmission rubber with bolts facing transmission ,and thr rear rubber fixing bolts facing axle . This may not be like the way your mountings are fitted to the shaft ,but idea is very much the same
 
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