Technical High speed vibration and pinion angle?

sound like you have it currently like image 4 You need to fix that.

 

Google phasing drive shafts-----it says if the trans is angled down 3 degrees you need to Raise the pinion 3 degrees to make them parallel. They are showing the same drive shafts images as above.

 

FWIW, I just read through my math post, and I missed describing something that will become important.
For perfect example #1, it's imperfect due to a rule of how u-joints work. What I didn't describe properly about why the front of the engine needs to come too, goes along with that rule.
THE RULE of how little of angle thru a u-joint, to promote needle rotation is minimum .5 degrees angle. With the given measurements, I came up with .3 degrees angle BEFORE correction of raising the pinion, which in turn, will flatten out that .3 degree angle. Again, .5 is the minimum, and we're already starting with less!
Even after the pinion angle is corrected, which is needed, correction needs to happen at the engine/transmission angle.
Lowering the rear of the transmission, or raising the engine is the correction, as the car has a one piece shaft.
FWIW, on Andy's comment about the '58 to '64 GM cars having been built incorrectly, those cars follow a different rule BECAUSE they have a two piece/three u-joint driveshaft. The shared rule is minimum .5 degrees angle thru each u-joint. The differed rule on a two piece shaft, and how you have to make angles work together is an algebra equation. I have a Dana/Spicer handbook, STG-789, that has an engineered formula wheel that can guide a knowledged technician on how to reset angles if necessary. I cannot describe how handy it is, and when used, how different vehicle subject vary so much on how to correct problems. My Spicer Driveline Selector handbook is well used, and costed $200 to my employer in 1993. It is as useful today, as it was before my hair turned gray.
On this subject car, the pinion needs to be raised, or left alone, and the rear of the transmission needs to be lowered to correct the problem. The goal is to get the u-joint angles within 1 degree of each other, and both above minimum .5 degree angle thru each of them.
My scars are hurting again, from working in the driveline shop for 25 years. Playtoys like this to vocational big trucks, I've done it, and to include performing corrections under those vehicles, after I diagnosed. I even taught classes today about that to the members of the Arkansas School Bus Mechanics Assn again, for the 7th time, annual seminar with factory vendor reps invited in. I'm a guy from the trenches and the parts counter.

 

British Leyland Motor Corporation/Rover built the absolutely not design, too.

It can be made to work, if you are a BCME.

 

After spending the day under the car on a lift at a friend's shop, I have new information that may hopefully shed more light on this frustrating problem:

1. I measured the driveshaft lateral alignment (front to back) and the driveshaft is perfectly centered in the frame, equidistant and both ends.

2. I checked the runout on the rear axles and both sides measure .003" or less at the axle hub.

3. I checked pinion runout at the shaft behind the yoke and that measured .003" or less.

4. Before making any changes, the following measurements were taken:
Transmission yoke/crankshaft angle = 2.8 degrees downward (towards rear bumper)
Driveshaft angle = 2.7 degrees downward (towards rear bumper)
Pinion angle = .3 degrees upward (towards the windshield)

5. I installed a pair of 2 degree shims (one each side) between the spring perches and leaf springs and recorded the following measurements:
Transmission yoke/crankshaft angle = 2.8 degrees downward (unchanged)
Driveshaft angle = 2.5 degrees downward (towards rear bumper)
Pinion angle = 3.8 degrees upward (towards windshield)

So if I understand the concept of what I'm trying to accomplish, I have moved the tranny and pinion angles to be within one degree of one another.

PROBLEM: The vibration is still present in exactly the same frequency (high frequency, audible and physical), speed range (72 to 78mph) and repeatability (always present). The vibration is constant with the clutch engaged or released at highway speed and does not appear to be RPM related, as it does not occur at the same RPM in lower gears/lower speeds. The vibration is present the same with a completely different set of wheels/tires than before (which have been balanced) as well.

Help? Any ideas on where to go now?

 

You still have .3 thru the front joint, and 1.3 thru the rear.
I feel like you have too little angle in the front u-joint, going back to my suggestion when I backtracked on my first advice. I've been known to make mistakes while trying to make corrections.
Would you mind pulling the caster shims out and trying to shim down the transmission crossmember to get more angle into the front u-joint, and flattening the rear u-joint?
Because it's a crossmember, I know that usually involves complications.
The problem you have is related to the pictures in the above post. Yours is related to the third drawing, with little to no angle thru the front u-joint, and pinion pointed up at the rear, even though the angle number looks OK there.

 

In my experience with leaf spring cars you want a negative pinion angle ( nose down ) when the rear end is under load the pinion is rising attempting to rotate all the way over, so if you start with a positive pinion angle ( nose up ) when you accelerate it will become more positive or over extended causing all kinds of issues. As mentioned above I can't recall seeing a pinion from the factory with a positive setting. If it were me I would put it down 2 degrees and see what happens.

 

In post 31 is that side view or birds eye?I understand that the second image, side view is correct. I cant even imagine image 4 existing in side view

 

TA DAD, it all depends on the altitude of the engine/transmission in relation to the pinion height before you set the pinion angle. I've had to work on enough trucks for a living to learn this, and to include correcting how I first set the pinion angle on my own hotrod.
In the case of this car, if you point the nose of the pinion down, you will increase the angle problem at the rear of the shaft, as you are making the front angle better.
It's a balancing act, and you have to have some foresight as to where your actions make all the pieces move.
I believe with this car subject, the objective will be to try to make the engine and pinion angles parallel, without lessening the u-joint angle so much that you drop below the rule of NO LESS than .5 degrees angle thru a u-joint, and in the case of a two u-joint shaft, both angles complimentary of each other as equal or within one degree compared to each other.

 

31 is in side view at horizontal, suspension loaded.

 

FWIW, I'm not looking at something else for reference material. I do have a manual from Dana/Spicer that describes how these rules are to be used, not the engineering math as to why. I'm using what I know to do with an angle finder in hand and a piece of paper to write component angles with, and go from there. Try a school bus with three shafts, and a suspension manufacturer tech guy on the other end of the phone with me.
I've been using this info since 1989 to perform some of the tasks that I use to make a living, and to have fun while helping folks.
This one is easy, as long as there aren't a bunch of hidden problems that act like a driveshaft problem can.

 

FWIW, depending on how the construction of a vehicle happens, some times the bird's eye view construction is necessary, and the angle rules still apply.
I apologize to anyone that could perceive me on a rant. This is not. I'm trying to teach as I advise.

 

No. That is not how u-joint driveshafts work.

The only situation when you want a pinion with a negative forward angle, in relation to the Earth is when you have exceptionally high torque (500lb.-ft.+), deformable suspension links (like leaf springs), and exceptionally high traction (all race applications).

If you have that much axle wrap on a street vehicle, you have a suspension problem, not a drive shaft problem.

I have been building high performance drivetrains for over 30-years, in several instances over 5000hp, seeing speeds in-excess of 300mph. I work with NASCAR K&N Pro Series cars, SCCA cars, IMSA cars, NHRA dragsters, SCORE trucks and buggies, SCTA "cars", and a ton of off-road stuff.

I have never seen an OEM vehicle that has a pinion with a negative forward angle. Perhaps you could provide a few examples.

 

All four of those are side-view.

#4 can be made to work, but you need to be an engineer, and to have full control over the vehicle/suspension design. A few manufacturers have actually done it. It is technically known as the W driveline design, or the "broken back" design.

 

Other things to check that can cause vibration:

Tire roundness.
Tire balance.
Drum balance.
Bushing and/or mount condition (engine too!).
Driveshaft balance.
Bent ears on the drivshaft.
Over tightened straps/u-bolts on the u-joints.
Worn tail shaft bushing.
Damaged/worn tailshaft yoke.

 

So, what we are saying using the side view perspective, 1 will use u-joints because of lack of angle, unless the overhead has the view of the second.
The overhead view of the first is good, combined with the side view of the second.
Drag car only for the third.
Careful application of the fourth. I had to use this one to make the driveline angles of my hotrod A chassis correct. I used the crank hole casting as a gunsight thru an empty block and transmission case to an empty 9" pinion retainer. The view of what I had to accomplish is upside down compared to the drawing. Engine nose up, driveshaft close to flat, pinion nose down.
It's about the math, and how to apply with the elements involved, and how some move.

 

And for those who don't want to get into advanced math:

Complimentary angles in relation to the ground plane. No harsh angles in relation to components and the shaft itself. Properly sized shaft components for the application/length.

 

Get the angles worked out correctly. Then if problem persists, check pinion bearings and/or preload. Tracked elusive vibration in OT pickup to light preload last week.

 

Some Studebakers used the "broken back" arrangement, (tranny down/pinion down) by running the U-joints out of phase, according to info I've found, and is probably what other manufacturers did with similar drivelines. As gimpy noted, setting one of theses up correctly is very involved.

 

I'm back to report that the issue has been resolved, and the culprit was the driveshaft...

I ordered a newly built aluminum shaft from American Powertrain. It's a 3.5" shaft vs. the original 3" steel shaft and weighs 9 pounds less. I also ended up with .5 degrees of difference between the tranny angle and pinion angle as recommended. Installed it and the vibration immediately went away.

I still don't know if it's because the steel shaft was bent/out of balance or if it's because the aluminum shaft has compensated for or masked some other drivetrain issue that may still exist, but either way, I can drive at 75 now without the car shaking apart!

 

3 to 4 deg. is what a U joint needs to not rattle.

 

I would second the alumium driveshaft. Had one done recently and was surprised how much smoother it ran. Also, increasing the diameter changes the resonance of the tube. The driveline shop said they have found that aluminum units can help in many cases.

 

No, not true. Three degrees is the maximum for a single cardan U-joint working angle for long like and high (around 5000) RPM. Anything more will reduce RPM potential with higher wear, vibration etc. Much better to keep the working angles over one but under three degrees.

 

For the aluminum argument, if you have an angle vibration problem, you're throwing money at a lighter driveshaft to hide the problem.
Some vehicles have a built in problem that takes an out of phase driveshaft to put in a cancelling vibration from the shaft to overcome it. 67-69 F-body GM is a perfect example.
And for all we know, we can build in the same type of problems with the customizing and construction of the types of vehicles we build. I've had to correct some of them while at my paying job. Some were even brand new custom large trucks that were being delivered to the dealership that ordered it, before being delivered to their customer. Some on dealerships honoring vehicle warranties and guided to my toolbox where I worked.
As far as maximum angle, the more you increase the RPM of the shaft, the maximum u-joint life span decreases based on angle. Lesser angle equals more life at a higher RPM, but you have to have at least .5 degrees of angle to make the needles revolve inside the caps.

 

You guys are funny

Go ahead and set up a hood less rubber raked car (4* nose down in the frame) that's also been lowered with that boiler plate 3* up/turnaround /down nonsense. I dare you.

Better yet, take a car that's been set up then throw a 4* rubber rake to it after the fact.

On these lowered cars, 80% of them have the pinion higher than the Trans output shaft and the drive shaft runs up hill to the rear.

 

The o/p said it cured his problem using an alumnium drive shaft. I would imagine no matter the cost he is happy to have it drive right. I found a similar result and thought others may benefit from hearing about it. I would never have thought it would make a difference. Yes they are spendy.

 

Did you use the same universals or did you get new ones?

 

Oh it would be new ones
And the pinion angle wound up within 0.5 degrees instead of 2.0.

There's a lot of dynamic change

 

New yoke, new u joints.


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