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Anyone want to try and explain this concept to a math moron? I read the theory at: [url=http://www.drivetrain.com/driveline_angle_problem.html>
<a href="http://www.drivetrain.com/driveline_angle_problem.html[/url]]http://www.drivetrain.com/driveline_angle_problem.html
[/url] and am not sure of what to check. I will try to explain what I think I read and see if there is any agreement.
If the transmission is fixed and at 3 degrees (down from level) and the drive shaft goes down at 6 degrees (from level) than, the rear should tip upwards 3 degrees? Because 6down-3down=3 then to get 3 degrees at the back you would need the front of the rear to be 3 degrees down from the centerline of the driveshaft 6down-3down=3 . So in this case if the rear of the transmission pointed down than the front of the rear end should point up the same distance? Or is the rear 3 degrees down from level (not driveshaft centerline). I hope some one can work with me to understand this. I made a tranny mount on one of my cars and have a mild nagging vibration that seems to be RPM oriented, but not in neutral. I want to be sure this is not the culprit.
Thanks,
Neil
 
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From what I know (which is not a lot..Ha) Imagine a line coming straight out of your transmission. Do the same for your differential. These lines should be parallel and that would be the correct alignment.

In a nut shell, if the engine is tilted 3 degrees up the differential needs to be pointed 3 degrees down to compensate.

This is what I know, take it for what it's worth.
 

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Easiest way is to see it on paper...

Draw a level line...pretend that is the ground

Draw line above it at one end which represents your trans tailshaft angle (say 3 degrees down) and then another line at the other end which represents your pinion angle (measured at the yoke)....disregard the angle of the driveshaft; for this purpose, it's irrelevant.

Compare the lines for the tailshaft and pinion...are they parallel? They should be...

Racers will run the pinion angle slightly down from parallel (on leaf spring cars) to compensate for spring wrap up and housing rotation upon acceleration. For most street cars, that's not necessary...

The easiest thing to remember is that, relative to the ground, if one end is down, the other needs to be up, preferably by the same angle...

Draw it out and it'll be obvious *G*
 

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Pat and others:
I've been reading this and other related threads, and I don't understand why the angles have to be parallel. Doesn't part of the function of the u-joints take up the slack/slop and allow a variety of angles to be had?
 

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Good point.....I was under the impression the angle had to be greater than parallel otherwise the needle rollers would not do their job.That's under ideal conditions,but our roads take care of that!!/forums/images/icons/wink.gif The trick is to get the angle from 0-3deg at rest,then the universals can do their job.
Greg
 
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Hey guys, I posted a similar question a couple days ago and think I understand the concept a little better now. The u-joints make up the difference in the vertical differences in the tailshaft of the tranny and the pinion of the rearend. By having the two units parallel (but not necessarily in line with each other) the angles at the u-joint connections are minimized which is the goal.
Micah
 

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Part of what is going on here is that the speed of the u-joint (hence driveline) is not constant as it rotates through 360 deg unless the driveline angle is 0.

If the driveline angle is greater than 0, the following occurs.
As the driveline rotates from 9-3 (visualize a clock here) it is deccelerating; as it goes from 3-9 is is accelerating (hope I got the right--it could be the other way around). Note that accelerating or decelerating is with repect to the average speed of the driveline.
It is a 'whip effect' caused by the driveline u-joint cups being closer to the transmission extension housing at 6 o'clock than they are at 12 o'clock. This amount is in direct relation to driveshaft angle.

In order to counteract this speed variation the axle u-joint angles should be phased (centerlines parallel) so that while the trans u-joint is speeding up, the axle u-joint is slowing down the same amount. For this to work, the angles must be the same, only complimentary.

You can actually see this in action if you remove the driveline from the axle, place it at a high downward angle and spin the driveline (trans in neutral).

BossBill
 

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O.K. Bill, you are gonna have to have another go at explaining that one to me.....just can't seem to figure out what you are reffering to. If the spinny bit (motor/geabox combination) at one side of a coupling is rotating at a costant speed (universal joint or not) and the other side of the coupling is rigidly attached (i.e. not through a fluid coupling or torque convertor or rubber joint etc), then surely both sides of the joint must be rotating at the same speed and there can be no acceleration or deceleration of the driven shaft??

Regardless of the angles, both universal joints would be rotating, and pivoting at exactly the same rate? The only way I can see there being any acceleration or deceleration of the universal joint would be if you are looking at the true definition of acceleration that includes vectors - where you are taking into account (looking at one end of the drive shaft only) the fact that on one half of the rotation, the gear box yoke pivot & drive shaft pivot points are moving towards each other, then on the other half, they are moving away from each other??? This, although acceleration by the true definition of the term, does not result in any changes in velocity of the shaft. The fact that the two pivot points do move toward and away from each other does provide the optical illusion of acceleration/deceleration though.

Or, am I missing something fundamental here????

J.B.
 

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Nice one JB.....I just about understood what BossBill was saying & you come along & throw a spanner in the works!/forums/images/icons/wink.gif I nearly.....finally, understood "Phasing"of the driveshaft.I have'nt worked the grey matter this hard for a long time.Now I'm getting a headache!/forums/images/icons/smile.gif
Greg
 

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Sorry mate...didn't mean to upset the old apple cart....but, I just can't see how a coupling, rigidly connected around the axis of rotation (i.e. pinned so it must rotate at the same speed as the drive side of the joint, but in this instance still allow vertical/horizontal movement) can allow acceleration/deceleration on one side of the joint but not the other..... Unless there is something I am missing (which is quite possible/forums/images/icons/crazy.gif)

J.B.
 

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I'll quote from http://www.4x4wire.com/tech/pinionangle/ -- maybe they explain it better than I can. I see they say it quite different as to opposing velocities canceling each other out. I think my explanation makes more sense, but I'm not a driveline expert.

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Here is the link to figure 'A' that's referred to in the article:
http://www.4x4wire.com/tech/pinionangle/ujnt.gif
Here is the quote:
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Improperly set pinion angle causes vibration which can lead to early parts failure. The vibration results from unequal velocities at the opposite ends of the drive shaft. When a U-joint is run at an angle the drive shaft will actually speed up and slow down twice during each revolution, due to the changing angular velocity of the U-joint ends.

Take a look at figure A to help understand why the drive shaft speeds up and slows down. The U-joint caps connected to the pinion yoke spin around the pinion without moving forwards or backwards, when viewed from the side. The U-joint caps on the drive shaft move forwards and back quite a bit when viewed from the side, causing a change in the speed that the drive shaft rotates.

There will be no vibration if the angles are the same at both ends of the drive shaft becuase both ends will speed up and slow down at the same time and in the same amounts. If the angles are off the U-joints will still cause the speed to change at the same time (unless the drive shaft is twisted) but in different amounts, causing vibration. Keeping the pinion paralell with the output of the transfer case will keep the angles the same, avoiding vibrations.
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I'm sure there are some interesting engineering formulas to describe what's happening here. That's beyond me.

BossBill
 

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Hmmm.....I agree with his statement that the "U-joint caps on the drive shaft move forwards and back quite a bit when viewed from the side", however, cannot see how this can possibly translate to a change in velocity of the drive shaft. Yes, you would get different velocities in the oscillations of the u-joint on each end of the drive shaft if the angles were not the same - this may possibly be the cause of vibrations - but, I still can't see the driveshaft speeding up and slowing down. Very interesting.

Thanks for the extra info Bill, I may contact this fella, and see if I can get more information out of him.

J.B.
 

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Been thinking more on the subject.....if one side of the tail shaft is speeding up, at the same time the opposite half is slowing down (which must happen by this theory as the shaft is continuously moving, and part of the shaft is always in the 6-12, and 12-6 half) - then one half of the shaft is going to overtake the other half!!! Now, that would be impressive to see!!

I've really got to find the answer to this riddle.....can't seem to stop thinking about it!!

J.B.
 
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