U-joint alignment on drive shaft - Team Camaro Tech
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post #1 of 7 (permalink) Old Sep 6th, 02, 02:28 PM Thread Starter
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Just pulled the drive shaft out of my wife's car to replace the u-joint. I notice that the ears for the u-joints are about an 1/8 of turn out of alignment. The car never had a vibration or anything to indicate a problem. There is no sign to show that it's twisted. I was always under the impression that they should line up. Should I install new u-joints and not worry about it or get another drive shaft. A buddy of mine has a spare one out of 68 parts car that I could use.
jamie
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post #2 of 7 (permalink) Old Sep 6th, 02, 02:35 PM
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It is fine. That is the way they were originaly built. I can give you the long explanation if you realy want it.

-Mark.
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post #3 of 7 (permalink) Old Sep 6th, 02, 03:33 PM Thread Starter
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stingr69, thanks, thats all I need to hear.
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post #4 of 7 (permalink) Old Sep 6th, 02, 03:46 PM
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O.K. Mark, I gotta know. I've talked with 2 different driveline builders & they couldn't explain why camaro drivelines are offset like they are. If you tell me, then I can slam dunk'em.

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post #5 of 7 (permalink) Old Sep 6th, 02, 05:24 PM
 
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yes, I am curious too.

I have, in the past, had cars both with a twist and without.

It made no difference that I could tell.
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post #6 of 7 (permalink) Old Sep 7th, 02, 03:25 AM
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The reason GM did it that way was an effort to reduce potential NVH (noise, vibration, and harshness I believe) issues with the driveshaft. They were trying to eliminate a certain type of potential vibration that can occur in the driveshaft when the yokes are "in time".

Think about a universal joint in action. The bearing cup will rotate on it's axis in one direction for part of a driveshaft rotation and then rotate the other way as the driveshaft rotates on it's own axis. As the yokes rotate, the loading changes. It is like a sinus wave.

GM did it for a reason, and yes, it is to cancel out the vibration at the zero degree of power transfer.
Power traveling through an U-joint is like a sine wave, the positive portion pushes the driving yoke against the driven yoke, the negative portion pulls the driving yoke against the driven yoke. When two joints are lined up on the same plane, the two sine waves are superimposed over each other, in-phase, the term is called.

At the point of every 90 degrees, there is an equilibrium of pushing/pulling, thus, the U-joints are loose, no power is transferring. GM went and offset one joint by 15 degrees to keep the joints under a constant load, thus, no rattles, no shakes.

Remember the example above, we have taken one sine wave and moved it about the X-axis by 15 degrees, no equilibrium point now. Driveshaft is always under tension.


Lots of theory and maybe practical application for a manufacturer of commuter cars. Not much of an issue to us performance oriented drivers with our loud exhausts and reduced (higher amount) NVH expectations. We just want to go faster and look cool.

-Mark.
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post #7 of 7 (permalink) Old Sep 8th, 02, 09:20 AM
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My local driveshaft shop told me it was done to reduce vibrations as you said. He also said it was abandoned as a practice because it really didn't fix the problem.

While on the subject, I have read in a forum post, that even though a stock driveshaft was balanced at a shop, there was still a vibration problem.
The driveshaft was then replaced with a new one, and the problem was solved.

I used to have terrible vibration problems with my 67, which started when I changed U joints. I think the factory balance was disturbed when I changed the U joints.

I have been paying attention to any driveshaft posts on the net, to learn as much as I can about them.

One of my main problems besides the balance being off, was having 4.56 gears and an engine that would wind 7000 in high gear. The driveshaft "critical speed" was being exceeded.
David

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