Driveline vibration after lowering car?

Many, many panteras have been lowered over the years. Also remember the car wasn't even designed to run with the shock spacers. They were added to meet US crash height specs. I have never heard anybody speak of their half-shafts vibrating because they lowered their car. Are you sure something else didn't come loose or changed?

Perhaps what you're experiencing isn't due to the rotation of the shafts at all. You wrote "...especially pronounced when hard on the throttle in a lower gear". Are the splines between halves of the shafts in good shape (well greased, not bent or broken, worn excessively, etc.)? What you may be experiencing is the shafts "locking up" when you accelerate and not being able to slide in and out smoothly, to compensate for irregularities in the surface of the road. In such a case, they won't slide in and out, they will "jerk" or "hammer" themselves in and out as the suspension moves up and down.

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Are you sure something else didn't come loose or changed?

Anything is possible, I'll have some time to check it out later this week...

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Are the splines between halves of the shafts in good shape (well greased, not bent or broken, worn excessively, etc.)

There doesn't seem to be excessive play in the splined area, but I'm sure they could probably use some fresh grease...

The more power you put through the shafts, the more difficult it is for the splines to slide in and out. If the vibration disappears when your speed is constant, on a smooth road surface, you’ve probably found your problem.

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There doesn't seem to be excessive play in the splined area, but I'm sure they could probably use some fresh grease...

well thats an easy fix then ;-)

UPDATE:

I finally had some free time to work on the car a bit last week...
From a previous post, the rear wheel camber after lowering was:

2.0 degrees - driver side
2.5 degrees - passenger side

I pulled out one .100" thick shim from each of the four lower control arm mounting points.
This brought the camber figures down to:

1.0 degrees - driver side
1.5 degrees - passenger side

I then used my adjustable upper control arms to dial out almost all of the remaining camber.
The figures are now:

0.5 degrees - driver side
0.7 degrees - passenger side

After making these adjustments, I went for a test ride.
The results were great, the vibration was almost completely eliminated!
I may tweak the ride height a bit more in the coming week or so.
Once that's finalized, I'll get the camber as close to zero as I can, and call it done.

Thanks to all for the help!

THANKS for the update and GREAT to hear of an improvement.

I like it when the theory can actually be verified in the real world. Only thing that could make your comments even better would have been if you could MEASURED the vibration magnitude before and after.

What is the vertical angle of the drive shafts now?

My mantra;
“when you can measure what
you are speaking about, …
you know something about it;
but when you cannot measure it, …
your knowledge is of a meagre
and unsatisfactory kind…” Lord Kelvin 1883

What about the grease situation?

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Originally posted by JFB #05177:
THANKS for the update and GREAT to hear of an improvement.

I like it when the theory can actually be verified in the real world. Only thing that could make your comments even better would have been if you could MEASURED the vibration magnitude before and after.

What is the vertical angle of the drive shafts now?

My mantra;
“when you can measure what you are speaking about, … you know something about it; but when you cannot measure it, … your knowledge is of a meagre and unsatisfactory kind…” Lord Kelvin 1883

It's true BUT it is not because we do not know or we can not measure a phenomenon that it does not exist or that it is unimportant.

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What is the vertical angle of the drive shafts now?

The vertical angle is still at roughly 7.5 degrees.

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What about the grease situation?

The shafts were well lubricated, and I added a bit of fresh grease for good measure...

Glad you nailed down the source of the vibration. I never meant to imply that U-joint can't work but that CV joints are more forgiving system. I don't know Pantera cars as well as others here but I doubt 0 degree camber is the optimum alignment for cornering using radials. Radials typically like at least a little bit of negative camber. If your car is just a cruiser without emphasis on cornering you're probably OK. Just be careful on those off camber high speed highway on ramps.

A powerful car with rear weight bias should have a rear suspension properly set up for the tires being used. Just my 2 cents.

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Originally posted by Racecar Mike:
Glad you nailed down the source of the vibration. I never meant to imply that U-joint can't work but that CV joints are more forgiving system. I don't know Pantera cars as well as others here but I doubt 0 degree camber is the optimum alignment for cornering using radials. Radials typically like at least a little bit of negative camber.

A powerful car with rear weight bias should have a rear suspension properly set up for the tires being used. Just my 2 cents.

Hi Mike,

No argument from me, the CV axles do have advantages:
- more forgiving
- no grease fling-off
- more exhaust clearance

As I understand it, the factory changed over to CV axles late in the production run...I'm not sure why.
I'll probably do the swap at some point in the future as well, but I wanted to find the root cause of my problem before doing so.

Also, I will be taking a very careful look at the rear wheel alignment in the near future.
Has anyone got any camber and toe-in specs for the tires I'm using?
BFGoodrich Radial T/A's in size 255/60-15.

Isolating the problem first is always a good idea.
One possible way forward is to find the factory alignment specs for a Pantera that came with similar size tires from the factory. Someone here probably has that info. These specs are likely to be a good starting point.

mpaschetto,
Please look for a PM.