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  #31  
Old 01-11-2018, 10:21 AM
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Donny's numbers are correct. Those are pretty severe working angles for a performance car.

I don't agree that lowering the pinion will get you proper working angles though. From what you are saying, your driveline/pinion angle are within .5 degrees of each other on the same plane. As you lower the pinion, you will move away from parallel angles. It will decrease your working angles, but the variance in working angles from driveline to pinion will increase. Right now you have 5.5 and 6-6.5. Lowering your pinion will spread those numbers which can also cause vibrations. I'm guessing that if you drop your pinion 2 degrees to .5 up, your pinion working angle will go to 2.5 and your driveline to 5. I think your tailshaft still needs to go up to get conventional working angles.

While the angles aren't great, they are parallel and appear to be within .5-1. I think you may have something else going on since the vibration comes in at such low speed and doesn't get worse. You may have two things going on here. A driveshaft issue and then your working angles may cause you vibrations with speed. I'm no expert on this stuff, but I fought the same situation on my car. If I kept that car, I would've cut the tunnel and raised the tailshaft.
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  #32  
Old 01-11-2018, 11:37 AM
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The driveshaft is running up from the transmission to the rear end, right?

If you roll the pinion down, the driveshaft also goes down in the rear, resulting in a lower working angle for both the front and rear u joints.

It's pretty hard to diagnose any vibration through a forum but the driveshaft angles are not good the way they are so it seems like a good place to start.
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  #33  
Old 01-11-2018, 11:46 AM
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Quote:
Originally Posted by dontlifttoshift View Post
The driveshaft is running up from the transmission to the rear end, right?

If you roll the pinion down, the driveshaft also goes down in the rear, resulting in a lower working angle for both the front and rear u joints.
Correct, but as Todd mentioned, the angles are nearly parallel just in different planes now. I've always thought that was the correct way to have the pinion angle and transmission?

Thanks everyone
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  #34  
Old 01-11-2018, 11:57 AM
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Forever the equal but opposite theory was the common theory that was regurgitated by magazines, driveshaft manufacturers, etc. and for most street rod swaps it worked. 3 degrees was the magic number, if you set everything there it would work and for the most part it did. But these aren't 40 Fords and the math doesn't work out.

The reality is that the u joint does not care about the angles on your pinion or your tail shaft and it especially does not care if they are parallel to each other.

All the U joint cares about is the angle that you are asking to work at.....and it wants to work at the same angle as the other U Joint. The lower the working angle, the happier the ujoint will be.



Incase embed doesn't work. https://www.youtube.com/watch?v=gmV4qwLfOMY
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Last edited by dontlifttoshift; 01-11-2018 at 12:00 PM.
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  #35  
Old 01-11-2018, 01:45 PM
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Thanks Donny. I'll watch the video when I get home. I appreciate the information.
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  #36  
Old 01-11-2018, 02:38 PM
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I ended up doing what Donny is saying on my car. Instead of cutting the tunnel I got my working angles as small as possible by lowering the pinion angle. I do think it caused an oscillating vibration over 85 on my car. The harmonics are no longer in sequence. It's certainly worth a shot.

If you have adjustable shocks, you could raise the car up as high as possible. That will effectively reduce your working angles and let you know if you are on the right path.

I agree though, 5-6 degrees of working angles is a problem regardless.
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  #37  
Old 01-11-2018, 08:31 PM
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Watching the video Donny posted, they reiterate that the working angles need to be the same between the two u-joints while showing the working angles at each end being fairly extreme. Which is more important? I can rotate the nose of the pinion up more easily than bringing the tail shaft of the transmission up. That would get my angles the same between the two joints but the angles would be more extreme. I'd be simply doing this as a test to see if it effects the vibration at all.

I swear I've done this before and it had no effect on the vibration. Then again, I swore my angles were good, too.

Also, if I were to nose the pinion down 3.5 degrees to match the tail shaft, causing the drive line to look like this \ _ /, wouldn't that cause the drive shaft to become unstable or bind?

Thanks everyone.
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  #38  
Old 01-11-2018, 09:00 PM
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Your current working angles per your measurements are within .5-1 of each other. 0-.5 is ideal so you are close.

What you are describing with the pinion pointed down 3.5 is exactly what I just talked about. You are getting your working angles on both ends of the shafts as small as possible. It takes some trial and error. The problem with this strategy is that you may get an oscillating vibration. When the working angles are equal and opposite, you get a consistent hum or vibration, when they are not you will get a stronger vibration followed by none.

Equal and opposite and small working angles gives you the smoothest operation.
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  #39  
Old 01-12-2018, 07:30 AM
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OK, I think I'm getting confused. I'm going to do some more reading and get back with you guys. I think I'm getting my terms mixed up or something.

Based on the measurements I have given, what is my pinion angle?

Thank you
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Last edited by WSSix; 01-12-2018 at 07:55 AM.
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  #40  
Old 01-12-2018, 09:56 AM
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Do this All angles are measured on the drivers side of the car.

1. engine/trans is on ____ angle and it heads down in the back. Meaning the crankshaft is higher than the tail shaft

2. The Driveshaft (if not there use a string or a piece of wood to go from the center of the output shaft to the center of the pinion) is at a ___ angle and it heads down in the back. The connection at the transmission & driveshaft is higher or lower than the connection at the rear diff to driveshaft. Does water from from the front driveshaft down to the rear or would it run from the rear to the front towards the engine

3. the pinion is at a ______ angle heads up or down in the back. The driveshaft and pinion create a V or a /\ ?. Would water placed on top of the diff run behind it or onto the driveshaft.

Base on this we will figure out the rest.


To give you an idea my angles were close but still caused a vibration and the aluminum bigger driveshaft fixed this. Mainly because the driveshaft was very level and caused a jump rope effect not to mention the driveshaft shop high speed balanced my new one.
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