Finding driveline vibration with Independent suspension - lifting and running to diagnose?

JHZR2

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I’m chasing a vibration in my 1982 300CD.

It comes on at around 40 mph. No real vibration in the steering wheel, though one front tire roadforce balances at 34 lbs (high).

I feel it primarily in the floorboard. With the car up (wheels on the drive on kwik lift), parking brake on, transmission in neutral, I can turn the driveshaft slightly. Maybe 1cm of play.

Center support bearing seems fine, flex discs, etc all seem ok.

Id like to lift the rear end, and make the car “drive”, wheels off the ground. Since it is an IRS, doing so with the wheels hanging will put a lot of force on the axles.

Is there a way to do this? Ferris Beuler style, up in the air, up on stands, run the vehicle. Don’t want to damage my axles.

Thanks!
 
Wont damage your axles, we literally do this every day.

Although, 34 lb of roadforce will likely be the issue.
The 34# tire is on the front left. Wouldnt/shouldn’t I expect some steering wheel vibration?

Not opposed to replacing the tire, but it is a $100ish endeavor. I suppose I could swap some 14“ wheels from my 240d onto the front to try first, but that’s another hour of time…

money vs time…
 
You probably have a tight u joint. You’ll have to remove the driveshaft and feel the u joints by hand to find it.
 
This is from another forum, but one of the members states his vehicle does the same thing as yours, around 40 mph.
 
Not for nothing.. I had a dodge dakota that had a driveline vibration. My hunch told me it was a u-joint on the drive shaft. I found a local driveshaft specialist and spoke with them. They charged me 200$ to replace the u-joints with high quality parts, and balanced the driveshaft. Truck was so smooth afterwards it was ridiculous. They grit blasted the shaft, replaced the u-joints, and high speed balanced the drive shaft. The position of the weights did move, and he told me that after around 100k, the weight locations drift some. I had such success I'm planning on balancing the driveshaft in my 2010 crown victoria interceptor. High speed vibration around 90 mph.
 
The 34# tire is on the front left. Wouldnt/shouldn’t I expect some steering wheel vibration?

Not opposed to replacing the tire, but it is a $100ish endeavor. I suppose I could swap some 14“ wheels from my 240d onto the front to try first, but that’s another hour of time…

money vs time…
Road force will be straight up and down, does not always cause steering wheel vibration.
 
You probably have a tight u joint. You’ll have to remove the driveshaft and feel the u joints by hand to find it.
That is a thought. These cars have a straight, aligned drivetrain, no need for angle changes, but it does have a u joint to allow for relative motion that the flex discs can’t absorb.

All mounts are good as far as I can tell… but drive shaft has crossed my mind.
Have you removed your driveshaft lately? If so, did you index it?

Drive shaft has never been touched. Looks like new.

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A14D3FD5-4677-4A2C-8603-46C709436397.jpeg

Not for nothing.. I had a dodge dakota that had a driveline vibration. My hunch told me it was a u-joint on the drive shaft. I found a local driveshaft specialist and spoke with them. They charged me 200$ to replace the u-joints with high quality parts, and balanced the driveshaft. Truck was so smooth afterwards it was ridiculous. They grit blasted the shaft, replaced the u-joints, and high speed balanced the drive shaft. The position of the weights did move, and he told me that after around 100k, the weight locations drift some. I had such success I'm planning on balancing the driveshaft in my 2010 crown victoria interceptor. High speed vibration around 90 mph.

interesting that the balance may shift.
 
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That is a thought. These cars have a straight, aligned drivetrain, no need for angle changes, but it does have a u joint to allow for relative motion that the flex discs can’t absorb.

All mounts are good as far as I can tell… but drive shaft has crossed my mind.


Drive shaft has never been touched. Looks like new.

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View attachment 75851
View attachment 75852


interesting that the balance may shift.
I had a 77 Z/28 where the driveshaft threw a weight. OMG, you talk about SUDDEN vibration! Luckily there was a good drivetrain shop at 688 Auto parts in Baton Rouge. They installed new U-joints and balanced it for $150 + tax.
 
I had a 77 Z/28 where the driveshaft threw a weight. OMG, you talk about SUDDEN vibration! Luckily there was a good drivetrain shop at 688 Auto parts in Baton Rouge. They installed new U-joints and balanced it for $150 + tax.
That could very well have happened here after 40 years…. Not sure why it would, but plausible all the same.
 
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