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post #1 of (permalink) Old 09-23-2001, 09:36 PM Thread Starter
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Driveline vibration and shaft question

Here's the deal: running a Tom Woods' long-slip CV shaft going from the X-fer to the rear axle. I've had some vibes for a while at higher speeds. When I spun the tubes, and had to drop the rear shaft to limp home HEY the vibe went away!!!

So today as we welded the tubes on the 20 and got ready to reinstall the rear d/s, I noticed the weights on the DS were all on one side. Thinking back, my last trail breakage saw a broken u-joint and the shaft separated and put back together (not necessarily correctly). So I pulled it apart and put the weights on either end facing opposing driections. The vibes were GREATLY diminished.

QUESTION: Assume that you have a CV shaft that has been taken apart and put back together incorrectly indexed. There are no "key" marks or anything noticible. On one end there are weights on 2 consecutive corners of the 4 on the CV unit. On the other end there is one weight on the shaft, near the U-joint. Is there any way to tell how it properly goes back together? Or must you take it to a D/S shop and have them balance it?

'83 CJ-7 nothing original but the tub and axle tubes
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post #2 of (permalink) Old 09-24-2001, 02:31 AM
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Re: Driveline vibration and shaft question

[img]/wwwthreads_images/icons/tongue.gif[/img] Don't forget that to balance a piece of shafting OR a tire, not only do you need to put the weights on the opposite side of the heavy spot, but you also need to put the weights on the same end of the shaft that the heavy spot was on. EXAMPLE: Let's say that you had a 1-1/2" solid shaft six feet long. It came from a steel mill in BANGLADESH and like most of the absolute CRAP that we get from overseas, was made from melted down 1972 Buicks. The shaft had internal porosity and was badly out of balance so you set it on some vee rollers and gave it a gentle spin with the palm of your hand. Soon the shaft came to rest with the heavy spot down. You installed a weight exactly on the top of the shaft on the far left end. You spun it again and it was more heavy spot. Then you got a great idea! Putting a mandrel in your fastest power drill, you chucked up a good sized rubber caster. Using the caster to drive the shaft, you spun it at a fairly high speed. The shaft proceeded to hop off the vee rollers and before you could back away, it smashed the crap out of your RH big toe, causing you to make new friends at the local ER. WHAT HAPPENED? The heavy spot on the shaft was actually way out on the RIGHT side, and when you got some RPM up, the two ends of the shaft hopped up and down, as the two opposite heavy spots really got things going. STATIC balancing is what you did not have DYNAMIC balancing, and the shaft proceeded to do the Watusi as the RPM increased. In the case of your CV shaft, the pieces may have been independently balanced statically, but depended on each other for dynamic balancing.[img]/wwwthreads_images/icons/crazy.gif[/img]

A Jeep Skunkworks run by Moonguys[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/tongue.gif[/img][img]/wwwthreads_images/icons/laugh.gif[/img], buildin' the ultimate SNOJEEP!
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