jdmick

85% of it is gone? Congrats! Damn pinion angles. I know what it's like to chase vibration problems. No fun at all. I was going to suggest a new shop to check the driveshaft balance and phase until I saw you had good success with a little offset. Congrats again!
I recall now that Norvalwilhelm was also a big proponent of using some offset to get rid of vibration. Seems the driveshaft needs some angle to it to run smooth.

pauldana

yea... seems to..... what it is, is that they need to have parallel plains. To be a little more specific here... there is no more sweet-spot as i described in the first post or so... when I hit the gas now or let go I have the same vibration, but down %85, in the sweet spot as well. ... so now I will go after that, I feel it is related to the engine, maybe even the exuast. we will see.... But it is the BIGGEST improvement so far.

OMF

How about checking the horizontal u-joint angles now. You may need a shim or two under the tranny mount to make the front and rear u-joint angles the same.

pauldana

YES I AGREE, I will be revisiting the vertical plan issues and take a new look at the rubber bushings now.....

TOYVET1 sent me this pm and said I can share it:
vibration
Trust me when I tell you have been through what you are going through , I have a 79 L82 4 speed since new. The SAME vibration nagged me for 7 years. I rebuilt the whole car chasing the vibration. After having the Super T10 rebuilt is was okay for abour 50 miles , and the vibration was back. The cause of the problem was the front driveshaft yolk was eating up the rear output bushing/ bearing. Closely inspect the surface of the yolk , I replaced the yolk and a new bushing. I have since put 5000 miles and steady as a rock at speed now. Hope this helps
Ken


Although I did this once (Or that is I paid someone to do this, and therefor probably not done right) I will recheck this and get a second opinion from a different tranny shop about the current slack in the yolk.... still cheep than pulling the trans and looking at the CF clutch... will update as soon as I can

I WILL FIX THIS!!!! even if it is the last thing I do in my life!!!!

builder

My vibration started around 69 mph and stopped around 83 mph. Smooth at all other speeds. I found that the top two bellhousing bolts attaching the tranny to the engine were loose/missing. Here is that portion of the story...

http://www.stovebolt.com/features/sa...g/index10.html

Vette80regon

even tho it sounds like your issue has been (mostly) resolved, for those who have a similar problem:
9 out of 10 times, unbalanced tires are the primary problem areas. If the car has been sitting for a while as indicated, this is definitely the issue (IMHO)

pauldana

ok... just got off the phone with fluidampr and they are sending me out a new 8" fluidampr this week... I will install it and report the results.. Also I will start a different thread soly focused on the fluidampr and its results... if this fixes the rest of the vibration, we have a winner!!!

pauldana

Ok,,,, fluidampr is sending me out a Fluidampr 8" HB this week.. I am going to start a different thread that only test the results of the fluidamper with video and pics. Then I will repost here for the overall work on this Vibration problem,

http://forums.corvetteforum.com/c3-t...post1570573593

pauldana

Well.... popped out the engine. changed the crank (I wiped it out) changed the HB, had the flywheel rebalanced (needed 2 1/4 holes drilled on one side to bring it into balance) changed the Centerforce DF for a new one. and this seemed to fix it all.... smooth as a babies ***... all the way up to 6500.... while I had it out I also changed the headers for superflow ceramic, and a Demon 750.... had it re-dynoed and It came back at about 15 less HP... now I am at only 400tq and 390HP at the rear wheels... o well.... but it is as smooth as I have ever ever had....


So, In conclusion, It was several different things, biggest was a alignment of the transmission and rear-end, second was the new balancing of the engine and flywheel.... now on the other things...

Thank you everyone for your input! CF is da bomb!!

OzzyTom

This thread seems to have a lot of info on driveline vibrations, so I'll add my solution too.

After fitting a Tremec TKO-600 box and a new 383 stroker, I experienced a cyclic vibration at 45~50 mph, which intensified like a sinusoidal wave at a frequency of about 2 Hz.

No issues below 45mph, no issues above 50mph.... But within that range it was very noticable... and that is the range that I am in when going through my favourite mountain twisties.

After measuring angles of gearbox, tail shaft and diff, the clear issue was that I had very little working angle in the rear uni-joint. The tailshaft and the diff were in-line, whilst the gearbox and tailshaft had a 2* angle.

What was needed was to raise the trans higher, but I couldn't due to bell housing fouling on firewall, and trans fouling on tunnel.

Not keen on pulling everything out to cutup the fibreglass, I put up with it for a while. It was tollerable, but annoying.

Anyway, when I replaced my diff, I also replaced the rear diff crossmember bushes, and added a tapered plate of 2* between the diff and the crossmember, to provide a working angle on that rear uni-joint.
Happy to say, the predominant cyclic vibration issue has gone.
There are other vibrations which now can be felt, but they are minor and add to the character of the car

volition

edit: I see you already solved it

jeffp1167

try rotating the driveshaft 180 degrees. Or have it balanced. I had a T=5 5 speed trans am doing this buzzing humming vibration and it was the drive shaft. same thing above 60 got noisy but decelleration quiet.

pauldana

Thx... solved this a while ago back.... but all are welcome to post there problem and fix here... it will only help us C3 vette people who suffer and suffer and suffer with the 10000000000's of things that cause vibration

Another problem i had was my Crank nose was fracked up by throwing the HB once...

old fan clutch was bad..... out of alignment transmission to rear (a big problem)

out of balance drive and half shafts

bad u-joints

and the list goes on....

I think i had all of them!!!

pauldana

started building a 4X4 rock crawler, so drive angle came up again,,,, I came across this, here is the web page and a cut and past.... very well written, and a good tag for this thread.

http://www.4crawler.com/4x4/CheapTri...line-101.shtml



Introduction:

Have you noticed a vibration or rumbling noise when you are driving down the highway? If you have a lot of miles on your truck, have modified the suspension or drive train in any way, you may be experiencing driveline vibration.

From what I've researched, ideally you want the two ends of a double-ujoint drive shaft within 1-2 degrees of each other for maximum u-joint life and minimum vibration. This is actually the operating angle (under load) and not the angle of the drive shaft to the u-joints themselves (that has its own limit).

Since the rear pinion moves up under acceleration (unless you have anti-wrap control on the axle) ideally you set up the static pinion angle to be 1-2° below the transfer case output flange angle. This way, as the pinion twists up, it comes into a good alignment with the transfer case. Typically, this figure won't be listed in any service manual, but I did find a reference from Ford that lists a static angle of difference of 1.7°.

In my case, I had installed a 1.5" longer shackle and a 3° shim to compensate for the extra tilt of the shackle. I never measured the angles at the time. Later, I did measure and found even with 3°, I was still 1° above the transfer case and I needed to add another 2-3° to get me passed zero and into the desired range. So I have to conclude that originally my pinion angle was off with the stock shackle as well. Driving experience also confirmed this, I had drive line vibration under load (pinion tips up), but it would go away under coasting conditions (pinion tips down).

So my point is to measure what you have now and see if its OK and how much will it change with a longer shackle.

I recently installed a CV-style rear drive shaft and had to tip the pinion up to point directly at the transfer case, so there a longer shackle works to an advantage. I calculated I would need an 8° shim with my 7" (3.5" longer than stock) shackle, but after installing everything, found my pinion was about 2° high, so I made a custom 5° shim to place it 1° below the transfer case line. If you need a custom axle shim, I may be able to help you out.

Terminology:

U-Joints:



The universal (or u-) joint is considered to be one of the oldest of all flexible couplings. It is commonly known for its use on automobiles and trucks. A universal joint in its simplest form consists of two shaft yokes at right angles to each other and a four point cross which connects the yokes. The cross rides inside the bearing cap assemblies, which are pressed into the yoke eyes. One of the problems inherent in the design of a u-joint is that the angular velocities of the components vary over a single rotation.
The universal joint was actually invented around 300 B.C. by the ancient Greeks. It was later re-invented in the 16th century by the Italian physicist Geronimo Cardano who used it as a mounting gimbel for holding a ship's compass horizontal in rough seas. Finally, it was re-re-invented in the 17th century by the English mathematician Robert Hooke who used it in its common form for transmitting torque. If that name sounds familiar, that is because he also is famous for Hooke's Law, which states that the stress in a spring is proportional to the strain (i.e. the spring rate). Where would 4-wheeling be without springs and u-joints? And I guess Hooke fooled around with a microscope looking at plant cells or something. So for some reason, the term "Cardan Joint" has stuck and is used interchangeably for a universal joint.
And note, it is "Cardan", not "Cardigan" which is alternately a sweater or a Swedish singing group
CV Joints:



CV (or Constant Velocity) joints are a class of joint which are designed to eliminate the variation in angular velocity that plagues u-joints, thus they are given the name Constant Velocity. The simplest CV joint is simply two u-joints connected end to end, usually the center section is called an H-yoke because of its shape. In this manner, the angular velocity variations of one joint are canceled by the joint on the other end. Since there are two joints, the operating angle capacity of the double cardan joint is twice that of a single cardan joint.
More complicated CV joints utilize a multi-ball bearing assembly that rides inside a cup-shaped housing that allow the center section to rotate in a different orientation than the outside part. Further variations on CVs allow for "plunge" or in and out travel of the center section relative to the outer section. A combination of the two is often used in FWD applications, where a plunge-type CV is used on the transaxle and a ball bearing CV is used on the outside. The plunge capability allows the drive axle to lengthen and shorten as the suspension travels. The outer CV can handle greater angles to allow for both steering and suspension travel.
A CV joint often requires special lubrication, usually an EP moly grease that is very sticky. On exposed CVs, a flexible boot contains the grease, on internal CVs, like the enclosed Birfield-type joint on 4WD front axles, the grease is packed around the joint inside the steering knuckle.
Single Cardan:

Single Cardan is a term for a driveshaft with one universal joint at each end of the assembly. So actually there are two single cardan joints in a single cardan drive shaft. Here's an animation of a single-cardan driveshaft as it rotates.
Double Cardan:

Double Cardan is a term used when describing a one piece driveshaft with three (or more) universal joints. What a double cardan will do, is split a universal joint operating angle into two separate angles that are exactly one half of the original angle. Normally a Double-Cardan (a.k.a. Constant Velocity or CV) style driveshaft is used in applications where it is not possible or practical to properly align the ends of a driveshaft for a single-cardan setup. Examples include where the operating angle would be too great over a single cardan joint (see below) a double-cardan allows the operating angle to be split across the two halves of the joint. It is also possible to use two CV joints on a driveshaft which is commonly used where it is not possible to align either end of the driveshaft, such as when both vertical and horizontal mis-alignment occur, or when mis-matched operating angles are present, such as in front wheel drive vehicles, where both up and down motion is present from the suspension travel as well as rotation about a vertical axis due to steering action. Drawbacks of multiple CV joints are their higher cost and complexity as compared to u-joints, their extra length and weight, and their decreased maximum operating angle limitations.
U-joint Operating Angle:

This is the angle formed between the two yokes connected by a cross and bearings. It may be a simple or compound angle, depending on the geometry of the driveshaft. While u-joints can operate at fairly high angles (usually up to 30°), the speed at which the shaft moves provides a practical limit to the angle as follows:
SHAFT RPM OPERATING ANGLE
5000 3.25°
4500 3.67°
4000 4.25°
3500 5.00°
3000 5.83°
2500 7.00°
2000 8.67°
1500 11.5°
This table is based upon the joint at rated load and life. Going above the rated load or angle will decrease the u-joints life. As a general rule of thumb, for each doubling of the operating angle, RPM, or load, the lifetime of the joint is decreased by half. Rated lifetimes are on the order of 3000 hours.
In the typical off-road vehicle, a suspension lift is done to increase clearance and allow larger tires to be installed. To compensate for the larger diameter, lower gears are installed in the axles. Lets see what this does for the drive shaft, the lift increases the angle of the shaft and the lower gears means the shaft has to spin faster for a given axle speed, both things are working in the wrong direction on this chart. No wonder, driveshaft problems are common in vehicles modified for off-road use. And what speed does the driveshaft operate at? Actualy, it runs faster than you think. Given a vehicle with a modest 0.85:1 overdrive gear in the transmission, the driveshaft is running nearly 18% faster than the engine is turning in top gear. So if the engine is turning 3000 RPM on the highway, the driveshaft is spiining over 3500 RPM.
Aside from u-joint lifetime, you also may be concerned with vibration-free operation at high speeds, at least for a street-driven vehicle. The maximum operating angle a given driveshaft can run depends on a variety of factors and is hard to give an exact number or formula to determine if a given setup will run smoothly or not. Some factors that come into play are the shaft RPM, the length and the tubing thickness. For example, a longer shaft can "soak up" more vibration than a shorter one and a slower moving shaft will vibrate less than a faster moving one. So, for an example. on my '85 4Runner I found that with the stock rear driveshaft running at about a 12° operating angle (approx. 4" lift, 50" long shaft), I had smooth operation. But when the shaft was shortened about 6" (due to adding a 2nd transfer case), the operating angle hit about 15° and I found it no longer operated smoothly, even with ideal u-joint alignment and a professional balance job on the shaft. So by converting the top u-joint to a CV joint and re-aligning the pinion angle, the shaft did run smooth again.


Measurements:

A frequently asked question is about driveshafts and angles and so forth, is "How much shim do I need for X" of lift" or "Is Y° shim too much?". Well, there really is no general answer to these general questions, rather the right answer is what works for that particular situation. For example, assuming that the driveshaft is aligned properly in a vehicle with stock suspension, if it is lifted with a block or spring lift, then everything should still be lined up, at least with a single-cardan driveshaft. It's like a parallelogram, the angles change, but the sides remain parallel. So why do some lift kit makers include shims with their kits? (Likely because they don't know what type of vehicle the lift will be installed on, so they supply parts that may or may not be needed in all applications). So the correct answer for how much to shim an axle to correct the driveshaft angles depends on how far off the angle is to begin with.

So, how do you go about measuring drivelines and angles, etc.? At first glance it seems kind of difficult, but I have some easy techniques that make the job very easy. How you measure the angles depends on the type of driveshaft you have:

Single Cardan Shaft Measurements
Double Cardan Shaft Measurements
Single-Cardan Measurements:

Assuming you have a single cardan driveshaft and want to check if the transfer case output and pinion flanges are close to parallel, just measure the distance between the top and bottom of each flange.
If the dimensions are equal, the two flanges are parallel.
If they are not equal, then each 1/16" difference is equal to 0.9° across the ~4" diameter of the flange (which is the size Toyota uses)
If 0.9° is too confusing for you, call it 1°, that is probably close enough for small differences.
Other makes may use different size flanges and some may not use flanges at all,
If no flanges are uses, then an angle finder must be employed to measure the angles
Ideally, you would like the upper measurement to be 1/16-1/8" less than the lower measurement for a bit of static "down-angle". Then, as the axle (and pinion) tilt up under load, the angles will approach parallel. While this measurement can be done with the driveshaft in place, it may be easier to do with it off, in order to get more accurate measurements:

In the above figure, you can see the red dimension arrow on top of the driveshaft and the green
dimension arrow on the bottom of the shaft showing the distance between the driveshaft flanges.
Note: some drveshafts do not use flanges, but the same concept applies.
Pardon the crude ASCII art that is supposed to show a typical driveshaft:
FT
-|\
-| \
FB\ \
\ \
\ \
\ \RT
\ |-
\|-
RB
The idea is to measure (FrontTop -> RearTop) and (FrontBottom -> RearBottom)
If (FT-RT) is equal to (FB-RB) then the angles are parallel
Ideally, (FB-RB) should be a bit longer than (FT-RT) at rest
Notes:
f your driveshaft doen't have flanges at the ends and instead has u-joint yokes, this technique may not work as well. In this case an inexpensive angle finder will do the trick. You may still need to be creative to find locations that allow you to measure the angles at the end of the shaft. See if the top or bottom of the differential or transfer case are parallel to the ends of the shaft or the u-joint yokes.
And notice that nowhere in this discussion has the actual angle of the driveshaft been mentioned. Why? Because basically it does not matter. What matters is that the two u-joints at each end of the shaft have the same angle. That exact angle would of course depend upon the angle of the shaft itself, but it is only the relative angles (or difference in angles) at each u-joint matters. So if you have a 10° driveshaft angle and 10° on the top yu-joint and say 11° on the bottom u-joint, you would have a difference of 1°. Now say the drivshaft angle were increased to 15°. Likewise say the upper u-joint angle also increases to 15° and the lower one to 16°. THe difference is still 1°, so as you can see the driveshaft angle itself has no impact on the operating angle of the u-joint themselves.
So, why do the u-joint operating angles need to be the same on both ends of the driveshaft? To understand this requirement, you need to see how a u-joint operates as it rotates. For an easy case, assume no operating angle, that is 0 degrees, between two shafts connected by a u-joint. As one shaft rotates through 360°, so does the other shaft, in exact unison, so at 0°, there is no issue.

Note, that if you only have one u-joint on the shaft, such as in a double-cardan shaft, it therefore must be at a 0 degree operating angle.
However, lets angle the two shafts to say 45 degrees. Now, look at the "cross" of the u-joint as it rotates. When the driving side of the cross is horizontal, it's ends are moving at the same speed as the yoke on the driving shaft. However, the driven side of the u-joint is 90 degrees offset from the driving side, but since the u-joint cross is rigid, all 4 ends are moving the same angular velocity, i.e. that of the driving shaft. However, since there is that 45 degree angle between the two shafts, the cross is also angled 45 degrees, meaning the effective length of that side is equal to the sin(45) times it's actual length or 71%. But, since it is moving at same angular velocity, the surface speed; which is equal to the angular velocity times the radius (or length); is now 71% of the speed of the driving shaft; i.e. the driven shaft is turning momentarily at 71% the speed of the driving shaft! Now, turn the driving shaft 90 degrees farther in it's rotation. Now the driving side of the cross is at 45 degrees, so it's effective length is now 71% and the driven side is 100%. Assuming the driving shaft speed is constant, then this means the driven shaft speed is now 1.00/0.71 or 1.41 times (or 141%) faster than the driven shaft! So, if you have the driving shaft turning at say 1000 RPM, the driven shaft will vary from 710 up to 1410 RPM as it rotates, averaging to 1000 RPM. This is what causes a driveshaft to vibrate.

So, how can such a setup ever work in the real world? As it turns out, if you stick another u-joint on the other end of the shaft and line it up in phase with the first one and keep the angles identical, these rotational speed changes nearly cancel each other out. While the driving u-joint is speeding up the driveshaft, the driven u-joint at the other end is slowing down what it is hooked to (usually the pinion on the differential). And while the driving u-joint is speeding up the driveshaft, the driven u-joint is slowing down the pinion. All this results in the pinion end of the shaft being driven and almost exactly the same speed as the transmision/transfer case end of the shaft.

I say "almost" becasuse the two u-joints do not even perfectly cancel each other out (except at 0 degree operating angle). The smaller the operating angle, the better the cancellation is, the greater the operating angle, the less the cancellation is. Also, if the angles on both u-joints are not the same, the cancellation is less good and if the two u-joints are not properly phased to each other, the cancellation is worse yet. In fact, if you were to go to the extreme and set the u-joints up 90 degrees apart from each other, not only would there be no cancellation but they would in fact compound the rotational vibration, the first joint would induce it's component, then the second joint would take that and multiply it by it's own factor depending on the angle. So, in the above case of a 45 degree operating angle, the driven joint would be running from about 50% to 200% of the speed of the driving joint, or from 500 RPM up to 2000 RPM for a 1000 RPM input. You can imagine what that would feel like driving down the road, say at an engine RPM the should give a 30 MPH speed, the tires would be turning anywhere from 15 MPH up to 60 MPH as they turned one revolution!

And if you don't understand the above (or believe it), have a gander at this animation and watch the center shaft speed up and slow down as it rotates.

Double-Cardan Measurements:

For a double-cardan driveshaft, you really do need to work with angles directly, that is you need to know the angle of the driveshaft itself and of the u-joint at the end opposite the CV joint.
How do you measure the angle of the drive shaft itself?
I use a Stanley digital carpenter's level (reads angles to nearest 0.1°), taking the sensing unit out of the carpenter's level housing. This level has a mode to read out in degrees. First, measure the angle of the drive shaft on the vehicle at rest. Then remove the drive shaft and place the level on the flanges it was attached to and get those angles.
Tip: if you do this, you don't need to use the technique in step 1 above.
Then subtract the drive shaft angle from the average of the two flange angles and that your static operating angle.
An alternate way to get this measurement is to measure the distance to the ground at both ends of the drive shaft and the distance between the two measured points and simple trigonometry (you do remember your trig, right?) will get you the slope, then you need a guesstimate of the actual flange angles. The transfer case flange is tilted down from vertical a few degrees on my truck.
You can also get a simple, inexpensive angle finder (this one is $5.99), one with a magnetic base is nice for attaching to the driveshaft. It should read to within 1° or so:

Pinion Angle: 68° Driveshaft Angle: 23°
Above, you can see how I measured the pinion flange angle, I clamped a piece of flat bar to the flange and placed the angle finder on it, gauge reads 68° which is equal to 22° from vertical (i.e. 90 - 68 = 22). The driveshaft angle is 23° (from horizontal). The difference in the to angles is 23° - 22° = 1°, meaning the pinion is 1° below the angle of the driveshaft.
One point to note is that my driveshaft doesn't really run at 23°, the above pictures and measurements were done on my sloping driveway, its about 8°, but it really doesn't matter, you don't need to be on a perfectly flat and level surface to do these measurements. Whatever angle the surface you are on is cancelled out, you only care about the difference of the two angles, not their actual values.
If you have a double cardan drive shaft, you want the end with the single cardan joint to be at right angles to the drive shaft itself. So, get the drive shaft slope and set the pinion flange to be at a right angle to it.
So determine the exact angle, find your driveshaft angle from horizontal and then set the pinion flange to the same angle from vertical
You may need to repeat this process a time or two if starting from scratch. As you tilt the pinion up, the distance the driveshaft has to drop from the transfer case is decreased, making the angle a bit less than measured un-tilted.
For example, when I installed new springs on my Toyota 4Runner, I decided to use a CV-style rear driveshaft. I used 3.5" longer than stock rear spring shackles to accommodate the longer springs, this gave me about 6 degrees of tilt, but I measured and determined I needed an additional 8 degrees of angle. After installing the 8 degree shim, I found the pinion is now tilted up a bit more than the driveshaft. I therefore designed my own steel shim at 5° to set the pinion 1°- 2° below the driveshaft angle to correct that problem.
What I didn't account for with the double-cardan setup is that as you tilt up the pinion, you are raising the pinion end of the driveshaft and thereby decreasing its angle.
I assumed this would be negligible, but I was wrong.
On my axle (a Toyota mini-truck axle, 8" ring gear), it is approx. 11" from the axle centerline to the pinion flange. If my driveshaft is about 44" long, then there is an inverse ratio of the respective lengths to the angle change. In this case, for every 4° of pinion change, there is 1° of driveshaft change.
In other words, if you need a 5° angle change, move the pinion up 4° and this will drop the driveshaft angle 1°.
If you have a single-cardan driveshaft and want to install longer (or shorter) spring shackles, you can determine the angle change quite easily. Just by knowing how much longer (or shorter) the spring shackles are compared to stock and the length of the spring, simple geometry will tell you the angle change. For example, on a Chevy 1500 2WD pickup, with 65" long rear springs, and with a shackle 3" longer than stock, divide the added shackle length by the spring length (3/65) and use the Inverse-Sin trig. function on a calculator to determine the angle. Using the Windows calculatr, enter the following 3 / 65 Inv Sin and see the answer is 2.7 degrees. In this case, a 3 degree shim is about what is needed to correct the angle change brought about by the 3" longer than stock shackle.
For setting the drive shaft length, measure it from flange to flange at rest. You should allow at least 1.25" of compression on the rear shaft and maybe a bit more in front (1.5"-2" - assuming spring shackles in back) to allow for the suspension compression. Then, be sure you have enough spline travel at full droop. If the existing spline length is not long enough (sometime a problem in the front drive shaft) a long travel spline shaft may be needed.

So, why must you run the u-joint at 0 degrees with a CV joint on the other end. See the discussion above and realize that the only time a single u-joint can operate smoothly is at a 0 degree operating angle. At any non-zero angle, the u-joint will induce a rotational vibration in whatever it is hooked to. This is not desirable, so the u-joint MUST be at 0 degrees operating angle in a CV- or double-cardan type shaft.

Phasing:

Phasing is a term that describes the alignment of the single-cardan joints on opposite ends of the drive shaft. As discussed above, a single-cardan (or u-) joint does not rotate at a constant velocity if the operating angle is non-zero. The drive shaft speeds up and slows down slightly as it rotates due to the nature of the joint. One way to reduce this is to make sure the joints at each end of the drive shaft are aligned properly. If the yokes on each end of the shaft line up with each other, as seen indicated by the light blue line in the figure below:



Then the affect will be that the two joints will tend to cancel out the speed variations from each other. In most 4x4 applications, the drive shaft will have a slip yoke in the middle to allow for changes in length. If the shaft is ever taken apart, it is important to get it re-aligned properly when it is re-assembled. One way to do this is to mark both sides of the slip yoke. However, you should check that the joints really do align properly, don't assume they are. The reason for the phasing is that the speed variation of the joint is related to its operating angle and its angle of rotation. In order to get the most effective cancellation, the joint yokes *must* be aligned exactly with each other and the operating angles must be identical. Any variation in either angle will show up as uncancelled vibration. While unequal operating angles result in a vibration that increases with shaft RPM, phasing problems may be felt at lower RPMs and higher loads, like when accelerating from a stop.

Most driveshafts will have some sort of alignment mark stamped or painted on to indicate the proper orentation of the slip yoke. If there is none, they try lining up the u-joint end caps as close as possible. One trick that can sometimes help with phasing is to spin half of the driveshaft 180 degrees before re-installing it to see if this makes any difference. Often one orientation may balance out better than the other. Once you find the proper alignment, paint a mark on both sides of the slip yoke so that you can get it back together correctly next time.

For a double cardan driveshaft, phasing is not an issue, although you may want to try and line up the bearing caps anyway.



Fixing Driveline Problems:

Most likely, if you've read this far (or even searched for this page) you may have a problem with driveline vibration or noise.

If you suspect vibration in the rear driveshaft, one way to isolate the cause of the problem is to remove the rear shaft, lock in the front hubs and test drive in 4WD, assuming your transfer case and 4WD system allow this mode of operation. If the vibrations remain, you've just eliminated the rear shaft as the cause of the problem, its likley to be a bad bearing, bent axle, out of round (or balance) wheel/tire, or something in the engine or tranny. If the vibrations go away with the rear shaft removal, then its something in the rear drivetrain that is the cause, the transfer case output, rear shaft (and center bering if present), the single and/or double cardan joints, the pinion bearing and rear differential could all be the cause.
If so, you probably want to fix it. How to fix it depends somewhat on what led to the problem in the first place.

If your drive shaft is has been damaged off-road (bent or dented) then this can cause vibration as well, a common problem is that the small balancing weights on the shaft can get scraped off on an obstacle).
If the shaft is damaged, it should be fixed. Typical cost for a straighten/balance is about $60.
If any of the joints or slip yokes are worn (i.e. if you can feel any play in any part of the shaft by hand) this should also be fixed.
For slightly loose joints, try greasing the joint well and see if it (temporarily) fixes the looseness and vibration.
I find that loose parts tend to vibrate under no-load conditions, like at speed when you just back off the gas pedal and are just coasting without engine braking. With no load, any loose part will make any vibration feel more apparent. And realize that almost all drive shafts w/ u-joints vibrate while moving even if perfectly balanced and aligned (it is perfectly normal), but if everything is tight, the vibration will be absorbed by the torsional stiffness of the shaft itself. But if there is a loose part, that will let the vibration be felt outside the shaft.
Check the transfer case and pinion flanges for tightness.
If they can be moved side to side by hand, they may need to be re-tightened or their bearings may be going.
And don't forget to check the dust shields that are pressed onto the back side of the flanges. Those can sometimes work loose and vibrate/make noise and lead to you think you have a "real" vibration problem, but may not.
If you recently lifted (or lowered) your vehicle's suspension by changing springs, adding blocks or spacers, or changed spring shackles, all these can affect the driveline angles, which in turn can lead to vibration...
So, assuming there is no physical damage or worn out parts, and you simply have an angularity problem, there are a number of ways to fix it. Basically, you want to correct the angles. How you do that depends on a number of factors:

How the angles got off in the first place
How bad the angles are, especially if the operating angle is greater than 10°
The type of driveshaft you currently have
What kind of suspension you have
How much work you want to do to correct the problem :-)
If you have a multi-link suspension, perhaps with coil springs, there are a few options. If the links are adjustable, you should be able to correct the angles with the adjustments. If no adjustments are provided, then you'll either have to get an adjustable link or relocate the suspension brackets on the axle.

If you have a leaf-spring suspension, then there are more options available. Among the options are shims, rotated spring perches, longer or shorter spring shackles, or driveline changes. Below is a table of common lifts and driveline affects:

Type of Lift /
Driveshaft &
Location Single
Cardan
Rear Single
Cardan
Frnt/Fwd(1) Single
Cardan
Frnt/Rev(2) Double
Cardan
Rear Double
Cardan
Frnt/Fwd(1) Double
Cardan
Frnt/Rev(2)
Spring None None None Tilt UP Tilt UP Tilt UP
Block None None None Tilt UP Tilt UP Tilt UP
Shackle Tilt DOWN Tilt DOWN Tilt UP None(3) None(3) Tilt UP
Lift Affects on Driveline; Direction to tilt the pinion to correct angles
Notes:

Front axle with shackles forward
Front axle with shackles reversed
Affect varies with length of spring, shackle and driveshaft length
Installing a shim between the axle and spring is the easiest way to correct the driveshaft angle (here's a convenient on-line source for custom-built axle shims). But which way does the shim go in to fix the problem? It depends on the spring and axle configuration, namely Spring-Over-Axle (SOA) or Spring-Under-Axle (SUA). The following table summarizes the direction of pinion tilt vs. axle configuration. and which way the "fat end" of the shim faces:

Tilt/Config Front/SUA Front/SOA Rear/SUA Rear/SOA
UP Backward Forward Forward Backward
DOWN Forward Backward Backward Forward
Pinion Tilt vs. Spring Configuration
Its best to visualize the spring as fixed flat surface under the vehicle. Then the shim will sit between the spring (top or bottom) and the axle, which then must rotate up or down to align the spring perch of the axle with the angle of the shim.

Conclusion:

And, a final thought on driveline vibration is that you need to think of the entire drive line as a system. It is not just a single angle or single piece of tubing or a single u-joint, etc. You have the shaft itself, 2 or more joints (single- or double-cardan), perhaps a center support bearing and then some sort of output spline or flange driving the shaft fron the transmission or transfer case and a similar flange at the pinion gear on the differential. You might find an angle is off, fix that and find that the vibration is still present. It is likely that with the angle being off, that induced vibration in the shaft that led to the u-joint(s) wearing out. So you replace the u-joint(s) and find the vibration is still there. It might be the case that the pinion shaft flange was loosened up by the vibration of the mis-alignment and/or the worn u-joint, etc. So the point is that you need to get the entire drive line all corrected/fixed at the same time to make it run smoothly as a system. So don't be put off if you find one issue, fix that and find that the problem is still there. You may have fixed the root cause of the problem, but now have other secondary issues (like worn u-joints or loose flanges) that need to be replaced/tightened as well.



Technical References:

4x4 Wire's Driveline Basics article is well written
Tom Wood has an excellent Tech Information section
Billa Vista's Driveshaft 401 page is also a good technical reference
Here is a writeup on using laser pointers for driveshaft alignments:
Ben Lee has a nice writeup of his driveline fixes and some alternate drive shaft geometries

RodWan

81 Vette, 60k, Auto 3spd, 350 w headers and side pipes.

Chasing down a vibration issue similar to that of this thread. Coming around a sharp right corner at speed I head a thunk and shift to the left. Since then I have been having a buzzing vibration roughly 55-65mph but it wonders. Under load accell/decel. Neutral usually makes it go away, but nor always. Had the ujoints replaced and getting the tires balanced now.

Pulling the rear apart I found the rear left strut had com loose ald could be moved in and out. New adjustable struts on order. But after reading the thread I'm thinking the jolt of the strut coming loose pulled the differential out of plane. Any thoughts? Based on the circumstances of when it began what else makes sense. I was thinking maybe I threw a weight, hense the tire balance. There is a tiny shimy to the trany yoke, but I don't see how the bearing there would have suddenly gone bad.

After the wheel balance, tire shop stated they were 1-3oz off and slightly out of round. I noticed a slight cluncky sound from behind the seat at slow speed 10-15, which I think is maybe the differential ujoint binding? There is a push-pull yawing movement too which I noticed before under slight accel from a stop, but there wasn't vibration before. I think it's the posi doing its thing.