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Date:         Mon, 16 Jul 2007 17:37:03 -0700
Reply-To:     Evan Mac Donald <macdonald1987@SBCGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Evan Mac Donald <macdonald1987@SBCGLOBAL.NET>
Subject:      Re: why "constant" velocity joints?
In-Reply-To:  <vanagon%2007071619251370@GERRY.VANAGON.COM>
Content-Type: text/plain; charset=iso-8859-1

A "constant velocity" joint maintains the same rotational speed all the way through a complete revolution. Because of its design, a standard "U" or yoked joint has one side speed up, then slow down TWICE in each revolution. Take a flex joint from your tool box - a 3/8 drive is easiest to see - and set it at a noticeable angle. Spin it slowly, and watch the "other"end, the end that is getting driven. As the relation between the yokes change, so does the relative speeds of output. This can be hard on all the pieces, trying to speed up and slow down twice, every revolution. Standard rear-wheel drive drive shafts have the yokes offset at 90 degrees to each other, so as one yoke tries to go faster, the other is slowing down. This way, the differential does not see any great differences in input rotation. Evens itself out, so to speak.

There are other considerations, including but not limited to, how much angle the joint is expected to flex, how much length variation can be allowed (yoked joints also get longer and shorter in their cycle!), and noise.

With short axles, and the variation in angle we see on our vans, CV is definitely better. But, it is more costly, in the short run. The manufacturer worries over that one.

Mark Hersh <markhersh@MSN.COM> wrote:

<SNIP> Now onto my first CV joint repack job in many, many years (didn't have a VW for a while).

Why are they called "constant" velocity joints, anyway? What is constant about the velocity, as they spin at the same varying speeds of the transaxle?


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