Driveline vibration after lowering car?

3 degrees is the recomendations for long life and least vibration. Besides the up/down angle you measured, you have to add the fore/aft.

the max angle is related to the rotational speed of the joints.

besides the shaft angle, the angle between the flange faces can contribute to vibration. Check the camber.

Thanks JFB,

I'll check the camber when I get home tonight.
I'm certain it increased when I lowered the car, will report back...

I brought this subject up a short while ago. not much in the way of replies. yes my car is quite low but still retain close to 4" of ground clearance. and I have figured this angle to be the cause after exhausting all other efforts. I do have adjustable upper A arms via eccentric bolts and modified upper mounts to accept them. thought about flipping my trans over but.. yea.no. Would be good to know if C/Vs would eliminate this (completely). Never noticed this problem with my Baja Bugs and sand rails but not the same apple.

U-joint vibration differs from the normal vibrations like an out of round or unbalanced tire. The vibration is torsional, that is;

While one flange is spinning at a smooth speed, the other flange turns faster for a ¼ turn, then slower for the next ¼.

During acceleration, the rear end is turning “smooth”, though increasing speed, where the tire is spinning with the jerking rotation.

How much of that jerk you feel in your seat depends a lot on tire stiffness.

During coasting, while your seat my not feel anything, the smooth spinning tire is now banging the gears in the rear end

CV (constant velocity) joints, done correctly, should eliminate the vibrations that you are experiencing. As Joe demonstrated, U-joint systems have changing velocity aggravated by high angularity and cause a torsional pulse preserved as a vibration.

Virtually no one uses U-joints for axles any more largely for that reason and for many years now units that can handle lots of power are readily available. Can you imagine a front wheel drive car with U-joints? Take a look at the wild angles Porsche cars have at there rear suspensions. Starting my build, I knew one of the first mechanical changes for #5715 would be CV joints.

When any one thing is changed from stock (ride height) there is usually collateral consequences. Often that's why people are unhappy with a mod.

I just finished measuring the rear wheel camber on each side of the car as it sits in its lowered state:

2.0 degrees - driver side
2.5 degrees - passenger side

Obviously, this is not optimal. Fortunately, this car has a set of adjustable upper control arms installed, and I could dial in the correct camber should I feel inclined.
I'll certainly make an attempt to get it closer to the ideal.
However, even after adjusting camber, I'd still be saddled with the 7.5 degree U-joint misalignment.

As an aside, I jacked the car back up to its previous ride height and measured:
U-joint angle - 4.5 degrees at ZF
1.0 degree camber - driver side
1.5 degree camber - passenger side

Which change had the greater effect upon the vibration, the U-joint angle or the camber angle?

quote:

Originally posted by mpaschetto:...

Which change had the greater effect upon the vibration, the U-joint angle or the camber angle?

Years earlier, I should have been able to run both equations of force and provide a quantified response. Just my rememberabce was that not having both flanges the same angle increased the jerk more.

asuming with your 7.5 degrees of the shaft, that the ZF will have its flanges true, so that end's angle would be 7,5
Now with 2 degress camber, that would actually reduce the flange at the wheel angle to 5.5

having ANY camber for driving stability is not good for u-joints

here is a vid

https://youtu.be/Idk3BVDVHq4

You can try reducing the camber to the minimum spec and see if that reduces the vibration enough.

quote:

here is a vid

https://youtu.be/Idk3BVDVHq4

Thanks for the link, that video was quite informative.

After watching, it would appear to me that the most important factor is to align the input and output shafts identically.
Driveshaft phase seems to be very important too.
The actual U-joint angle seems less important as far as vibration is concerned, but is important for longevity.

At least that's my take...

quote:

Originally posted by Racecar Mike:
You can try reducing the camber to the minimum spec and see if that reduces the vibration enough.

I will certainly reduce the camber to some degree, how much is not known at this point.

In any event, I'll most likely do the CV swap anyway.
In addition to alleviating the vibration issue, the CV axles would allow me more exhaust
clearance, and hopefully put an end to grease flinging all aver the underside of my hatch.

quote:

Originally posted by mpaschetto:
..the most important factor is to align the input and output shafts identically.
Driveshaft phase seems to be very important too.
The actual U-joint angle seems less important as far as vibration is concerned, but is important for longevity.

At least that's my take...

Good take...
again, don't feel like doing any math; I think the "angle" determines how much the mid shaft jerks. If the two flanges are EXACTLT the same angle, there will be no rotational jerk in the drivens rotation.

The midshaft jerking wears the ujoints, splines AND induces its vibration to the elements it is attacted to.

THEN, with the two flanges slightly mis matched, the magnitude of the force transmitted depends upon the magnitude of the midshaft jerk.

(I don't think I am conveying thought)

first, the transaxle MUST be set level so that its flange faces are true, then with "O" camber the two end's angle will be the same.

Like the Spicer recomendation to keep the angle under 3 degrees, they recomend the differance be less than 1 degree. Thus setting camber to 30' (half of a degree) would be within thier limit

A few Pantera owners have adapted big-block Fords & 454 Chevys to the Pantera, and because that's a longer block, the whole powertrain is shoved backward some 4" to get the block out of the cabin. The ZF is back so far in such Panteras, the AC evaporator in back must be relocated for clearance. Such cars have run the Silver State Open Road races in NV and the famous standing-mile acceleration events- first at Maxton, N.Carolina, then recently at the Mojave Airport in S. CA.

One of the faster Panteras at Mojave at around 158 mph avg over the mile was Darryl Johnson's 545 cubic inch car in 2016 (?). Jr Wilson was famous in the '80s-'90s with his bored & stroked Boss 429 in a Pantera w/just under 900 bhp. That car was clocked at many SS events at well over 220 mph for the 92 mile long event, and the longitudinal u-joint angularity from the relocated powertrains in all these cars was nowhere near 'ideal'. I guarantee, those big-block cars are pumping far more torque thru their tires than your machine! Your moderately lowered car has a vertical angularity into the u-joints that should theoretically have the same relative effect. So based on the many successful big block conversions, I think Hooke type u-joint angularity as you describe it will be a non-problem for your Pantera, except maybe at LeMans or other long duration pro races. Excessive lowering in front can cause severe handling problems unless 'other things' are done, but IMHO the amount you've lowered your car should be undetectable on the street & give good stock u-joint life. Do not overthink the problem.

The dynamics of a load going through a shaft with joints is fairly complex. The YouTube is a good starting point to better understand what happens when U-joints are used. There was no load on the demo rig. If the car's drive components were perfectly lined up then both systems would work about the same but it's a dynamic system. The further away from perfect alignment (an impossible arrangement) the less tolerant U-joints are. Don't forget about camber gain during suspension compression and the slip joint (splined joint) friction. SACC has two good CV systems worth considering.

quote:

...but IMHO the amount you've lowered your car should be undetectable on the street & give good stock u-joint life. Do not overthink the problem.

Hi Bosswrench,

Thanks for popping in and taking a look at this thread...

I don't doubt that other cars have had success with the OEM halfshafts, even the modified cars that you mentioned.
But that doesn't change the fact that I do have a driveline vibration with my car.
There are not many parts that rotate outside of the wheels, tires, and halfshafts, so that's where my troubleshooting began.
And since the vibration was aggravated by lowering the car, I immediately faulted the halfshafts.

When I open up the throttle in any of the lower gears, the vibration is so bad that the shift lever feels like its going to shake right out of my hand!
I am absolutely not opposed to doing further, in-depth troubleshooting to figure this out.

If there is another issue (or issues), I'd love to find it.
Any ideas where to begin?

Yes, I think you should go back and check again if the shafts are "in phase". The bearing caps must be at the same angle and if the slip yoke has been disassembled and not put back together correctly you will have 2 vibrations per every revolution. The half shafts rotates about 1400rpm @ 100 mph so its fairly low rpm compared to i.e. a propshaft which usually follows engine rpm´s in the final gear. Also if the slip yoke is severely worn it can contribute to being out of phase I suppose. But check the phasing again! there are arrows marked on the 2 parts that must align.

quote:

Yes, I think you should go back and check again if the shafts are "in phase".

Goodroc, I took your advice and triple-checked the half-shafts this morning.
They are definitely in phase...

ok, try and have a quick look at this video (if you did not see it already)

Something must be off with your shafts.

https://www.youtube.com/watch?v=z2C2eMMKf4M

Do you belong to a Pantera club or know anyone with spare parts? Borrowing a pair of halfshafts or even wheels & tires for debugging has been done before among club members. There are members of the PONE (Panteras of the North East) Chapter of POCA up your way. I'd hate to see you spend time and stomach lining on all this with halfshafts, then find that one wheel has dropped a balance weight.

To set your mind at ease and eliminate the halfshaft assemblies as the actual cause of your vibration, take/ship both halfshafts to a shop such as Driveline Specialists and have them expertly inspected and spin-balanced. Worn yokes sometimes have oversized holes for the u-joint ends to press in, resulting in a loose fit. I've seen yokes in which u-joint ends literally fell thru or had cracks.

If a very close examination of the u-joints, yokes etc show actual shiny spots from metal-to-metal contact, perhaps some extended-range u-joint assemblies would help. The driveshaft shop will know if that's even possible or necessary.

For the small amount you say you have lowered your car, there should have been NO effect except the need for a 4-wheel realignment. You could also easily return the chassis to whatever the non-vibration stock height was, and see if the vibration is still there or if it vanishes.

quote:

Do you belong to a Pantera club or know anyone with spare parts?

Hi Bosswrench,

Yeah, I'm familiar with many of the local Pantera owners in the area, including our chapter president.

I'll dive into more in-depth troubleshooting after the weekend. There is a very capable driveshaft shop local to me that I've used in the past. If I don't find anything obvious, I'll have them take a look at the half-shafts.

I'm with you, I didn't feel there should be any trouble at my new ride height. It is set so the lower control arms are parallel with the ground, not really that extreme in my opinion.

Thanks for your help!

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.

quote:

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...

quote:

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.

quote:

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?

quote:

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.

quote:

What is the vertical angle of the drive shafts now?

The vertical angle is still at roughly 7.5 degrees.

quote:

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.

quote:

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.