Drive Line Angle will drive you crazy

HWYCRZR

Old Man with a Hat
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As my radiator is out and had some some time on my hands I decided to start chasing my 80 MPH vibration. I don’t believe it to be my tires as I have rotated them and it didn’t change a thing. So based on a discussion in @CanCritterAnd
@Ross Wooldridge 1971 Plymouth Sport Fury GT Brogham & U code Super Comando mentioned checking the drive line angles.
I first got out my service manual and read through the specs. I started out with a small 6” bubble level with a leveling screw and tried to follow the process.
First issue was finding a flat spot on the engine and transmission. Of course the service manual says use tool SP 5060 and adapters. I don’t have that tool nor does it come up in a google search. The area is tight enough that it is difficult to get a level up there, so I made my own adapter the would sit on the block by the oil pan. This Plywood adapter clears the tie rod and exhaust. This allowed me to measure the angle of my engine and transmission.

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Also on the 8-3/4 rear end you need to remove the upper bumper plate to access a flat surface that is in line with the rear pinion.
One thing to note is you need to measure everything on the same side with the level in the same direction, or your readings will be off. Anyway I tried to follow the book using my little spirit level and discovered that I was a little off. At issue my bubble level did have the same range and gradients as the Chrysler one. I could tell I was off, but not how much. One important thing I noticed was my pinion was pointing the opposite direction as my engine and transmission. That may cause some vibration issues.

I tried to illustrate.
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The dotted lines are supposed to be Almost parallel to each other.
Ross has a great example here.
From the innerweb:

"The pinion angle is simply the angle between the rear end’s pinion shaft and a true horizontal line. The transmission angle is the angle between the transmission’s tail shaft and a true horizontal line.

View attachment 385948

Together, these angles form the driveline’s phase angle. Pinion angles can make the difference between a smooth ride, or a noisy and vibrating ride. Correct pinion angles are also very important to the life of your u-joints. Yes a driveline will work with 0* degree pinion angle, but the u-joints need a slight angle for proper lubrication. Without the correct angles, the needle bearings in the u-joint caps do not rotate. Those needle bearings need to rotate in order for the u-joint to operate reliably and smoothly. These u-joint angles should always be at least 1-degree to avoid wearing out the yoke bearings."
 
Its possible your driveshaft is out of balance. I chased a shake in the steering wheel at 60mph. No matter what wheels I used, tires ect. I had my driveshaft shop balance it. The shaking went away.
 
Ok I seem to be a little out of whack. My nice little bubble level is left in the dust for a more modern digital angle gauge.
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The service manual doesn’t give you any actual angles just bubble position so more googling was in order. I found a site that explained the math and had a link to an app that will work with your cell phone. The key again is to measure everything from the same side and keep your phone or level going the same direction. If you flip it you may get some odd readings.
Driveline Angles 101
This site had a u tube demonstration and some information. I found the app quite handy, however there measuring description is not the best as they want you to measure things from 90 degrees and then convert.
I will explain the math next.
 
Its possible your driveshaft is out of balance. I chased a shake in the steering wheel at 60mph. No matter what wheels I used, tires ect. I had my driveshaft shop balance it. The shaking went away.
That is a good possibility as I do have some dings in it. Mine starts at 80 and isn’t much of a steering wheel shake and is more of a resonance that seems to me coming from the transmission tunnel.
However my OCD is making me make sure my driveshaft angles and alignment are at the optimal angle. Then I will move to my drive shaft.
 
A drive line with even small dings will sometimes not run true. If you going to have the balance checked, have the run out checked also.

Dave
 
Drive shaft angle. This is a combination of the difference between the transmission angle and the drive shaft and the pinion angle and the drive shaft.
Ideally you want everything sloping towards the same direction starting from the front of the vehicle. More than 3 degrees difference between the two angles is considered excessive. And the total angle should be less than 2 degrees.
Before I started messing with the pinion angle, I had the following:
Engine/ transmission 3.8 degrees down
Drive shaft 2.7 degrees down.
Since both are down you subtract. If one is up and the other down you add. 3.8-2.7=1.1 degrees, this angle is More than acceptable.
Now the second angle. Pinion 0 degrees and drive shaft 2.7 degrees. 2.7-0=2.7 degrees. Rear angle of 2.7 degrees. Technically under 3 degrees. The total angle is the difference between the two angles. 2.7- 1.1= 1.6 degrees technically within spec with each angle being under 3 degrees and the total under 2 degrees. Since the pinion angle is flat I wanted to experiment to get the second angle a little closer to nominal and the total angle under 1.
I don’t have real pinion wedges so I used some resin shims which are about 1.5 degrees. ( experimental purposes only. They do hold up houses though.) What Didn’t realize was that when you add the shims it changes the drive shaft angle to the front making that angle fail. This means I need to add shims to the transmission to lift the tail up to get my front angle back in spec.

experimental shims
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I added 2 -1/8” shims between the transmission and mount.
I made some from 2” wide steel.
AF5936D7-46CA-4896-A49A-81CD285E5CDD.jpeg

Now that I think I have it I am going to measure with a simulated full tank of gas and a loaded trunk and compare it to the angles at just under 3/4 tank of fuel (current level).
Angles fully loaded.
Engine/trans 4 degrees
Drive shaft 2.4 degrees
Pinion 1.4 degrees
All Angles going the same direction.
Front angle is 1.6 rear angle is 1 degree. Total angle .6 degrees.
Junk in my trunk.
31E8A2D9-9189-4587-83D6-74EF8725D291.jpeg

Now at cruising load. 3/4 tank of gas.
Engine/ trans 3.6
Drive shaft 2.6
Pinion 1.4
Front angle 1 rear angle 1.2. Total angle .2 degrees
From what I hav read you do not want 0 as your total angle. They say it doesn’t put enough load on the U joints to rotate the bearings.
I did order 2 degree shims to put in. I used a jack to lift the pinion to two degrees and calculated total angle. It came in at .6 which should be pretty good. Also my transmission pan sits flat within a half a degree.
You can check my math if you want.
Did it stop the vibration? Not sure yet. I am still waiting for my radiator to get finished re-cored. Hopefully tomorrow.

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A drive line with even small dings will sometimes not run true. If you going to have the balance checked, have the run out checked also.

Dave
I have a magnetic base dial indicator. I could check the runout by manually turning the drive shaft with the rear wheels up while it is on my lift.

Yes drive shaft work is probably in the future.
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Very cool - I am following with interest.

Definitely one would have a problem if both the rear AND the trans were not sloping in the same direction... and I would have thought that the resulting vibration would have been teeth chattering... but looking at your drawing, I think I read it as they are sloping in the same direction, just not at the same slope, and therefore the pinion angle and the trans tailshaft angle are not on a parallel line which is the issue.

From your attention to detail, you'll get this worked out nicely. The driveshaft will be the sweetener.

Keep in mind, that if the above planes are parallel, suspension flex due to carrying a load (passengers, junk in the trunk, full of gas or empty etc) is a relatively dismiss-able factor, as by design the angles are designed to stay the same under such varying conditions. Otherwise one would experience vibration at just about any condition other than optimal.

Keep us posted.
 
Very cool - I am following with interest.

Definitely one would have a problem if both the rear AND the trans were not sloping in the same direction... and I would have thought that the resulting vibration would have been teeth chattering... but looking at your drawing, I think I read it as they are sloping in the same direction, just not at the same slope, and therefore the pinion angle and the trans tailshaft angle are not on a parallel line which is the issue.

From your attention to detail, you'll get this worked out nicely. The driveshaft will be the sweetener.

Keep in mind, that if the above planes are parallel, suspension flex due to carrying a load (passengers, junk in the trunk, full of gas or empty etc) is a relatively dismiss-able factor, as by design the angles are designed to stay the same under such varying conditions. Otherwise one would experience vibration at just about any condition other than optimal.

Keep us posted.
As I am reading through some of this stuff I am finding that perfectly parallel angles are not the best either because there is not enough preload on the U-joints to turn the needle bearings resulting in premature wear. As you said the key is the angles going in the same direction. Per the TREMEC app the allowed total angle should be fine up to 2 degrees. The app is kind of cool as it will give you hints as why the angles may not be in the green.

Still learning.
 
I am not sure what the runout tolerance is. I am thinking that I am on the excessive side.
Rear is about.020 and the front goes up to.030
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That shaft with the ding in it is toast, at least from a technical standpoint. If it ever has a serious load run through it, that ding is where it will fold up go boom.

Kevin
 
While looking at your post with interest I couldn't help but notice how clean everything is. No too many things nicer than a squeaky clean undercarriage. Nice work, I'll be following. Good luck
 
You should never get 0° angles and the car design prevents this no matter how the car is loaded. There is a offset in vertical plane to prevent the driveshaft ever lining up the u joints. At normal ride height getting them closer is okay but it is a constantly moving target, thus the vertical plane offset. The run-out is from the yoke ears being bent mostly from some gorilla that beat the u joints apart when replacing. Nice work keep it up.
 
I think that there is a difference in what people are saying and what I'm understanding their saying in terms of the definition of "0 angle"...

My understanding is this:

The tailshaft and the pinion should be at the same angle but on PARALLEL LINES/PLANES, with the driveshaft connecting the two parallel lines between the the U-joints... and therefore BOTH the U-joints are always at an angle when operating... allowable discrepancy between those angles should be as small as possible, with 0 degrees difference being optimum. I do not believe this is where one wants ANY difference, as this will set up a vibration as the U-joints struggle to equalize at different rates. This is where one DOES want a 0 degree setup. In parallel with 0 angle is good...

If the tailshaft and pinion AND driveshaft are all on the same line and not running parallel, then there are no angles on the U joints and hence a 0 DEGREE ANGLE SETUP, which is not desireable for two reasons I can think of right away:
1) no load (equalized) on the U-joints,
2) every movement of the rear suspension will set up unequalized (non-parallel) angles in the U-joints causing wear and stress. The parallel lines/planes design is critical for proper operation to ensure by design that the lines/planes stay parallel under all situations.
This is where one does not want a 0 angle result. Single line/plane installation with 0 degree angle (or any degree) is bad...

Not being critical here of any previous posts, but wanting to make sure that all of us are on the same page in understanding of the definition of the term 0 degrees in this instance.
 
You should never get 0° angles and the car design prevents this no matter how the car is loaded. There is a offset in vertical plane to prevent the driveshaft ever lining up the u joints. At normal ride height getting them closer is okay but it is a constantly moving target, thus the vertical plane offset. The run-out is from the yoke ears being bent mostly from some gorilla that beat the u joints apart when replacing. Nice work keep it up.

What are you calling me a gorilla? :D
The yokes being tweaked could be part of the cause of failing a U- joint around 2,000 miles. (well creating more radial play than I was comfortable with.)

Thanks for the input
 
That shaft with the ding in it is toast, at least from a technical standpoint. If it ever has a serious load run through it, that ding is where it will fold up go boom.

Kevin

Yes it is probably time to find a good driveshaft shop. I know of a good rear end shop here in town that has been in business for years. They say they have a good driveshaft shop down in SD. He doesn't like the work and the turnaround time of any of the local shops.
 
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