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Date:         Tue, 14 May 2002 22:07:40 -0700
Reply-To:     DaveC <voicebox@DNAI.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         DaveC <voicebox@DNAI.COM>
Subject:      Re: rotating cvs and axles from left to right
Comments: To: mark drillock <drillock@earthlink.net>
Content-Type: text/plain; charset="us-ascii" ; format="flowed"

>No, this is wrong. It is not the direction of rotation that matters. It >is the direction of force. Read Karl's procedure again. > >Swapping end for end on the same side does not help. Only swapping from >side to side changes the direction of force on a given CV. > >Check the archives, this comes up over and over again.

-=-=-=-

Mark is right: Karl is right. (And what about Karl Marx? And don't forget Groucho!)

After some careful finger fiddling, I've become a convert. If you want to understand WHY the swapping works (or doesn't), follow along.

(Don't operate heavy machinery, drive, or consume mind-imparing substances when doing this; you may damage your brain or other organ in ways you won't be able to repair...)

Or you can skip down to the end and read the conclusions.

You can model a CV joint by slightly interlocking the fingers of both your hands.

First model the left inner CV. Imagine one hand (the right one, for this example) is the driving force (transmission output torque), and the other one (the left, unless you've got more than two) the axle.

Rotate your right hand lightly clockwise against your left. Notice which sides of your fingers press together.

Now model the left outer CV. Imagine your right hand is the axle, and your left one the wheel. You will still rotate your right hand clockwise against your left. Notice that the same sides of the fingers press together. Ergo, the CV's on one axle have the same load pattern, the same wear direction.

Model the right side CV's similarly and you'll see that the load pattern is opposite (the other sides of your fingers press together). Ergo, the CV's of the two axles wear oppositely.

Still with us?

Again model the left inner CV, but this time swing around in your Captain's chair and imagine you're facing the rear of the Vanagon. This is how you represent swapping an axle end-for-end, keeping it on the same side of the transmission. Since you've changed the direction of rotation, the left is now the driving hand, and the right the axle. Rotate your left hand clockwise against your right. Notice that the the same sides of your fingers press together. Ergo, the wear pattern remains unchanged if you swap an axle end-for-end.

Now (facing forward again) model the right inner CV. The left hand is the driving force, and the right one is the axle. Notice that the opposite sides of the fingers press together compared to the left CV's. Ergo, the wear pattern reverses (opposite sides of the balls n' grooves) when you swap an axle side-to-side.

So, what have we discovered, class? 1. Swapping an axle side-to-side will wear the other side of a CV's grooves. This may or may not extend the life of CV. Only extensive testing can determine this. 2. Swapping axles end-for-end gives no wear benefit; it's completely optional. 3. The balls in the CV's, by their nature, wear more or less evenly (a ball rotates constantly in its groove, regardless of load direction). This may be the reason a CV's life can't be extended (if, in fact, it can't); no matter how you change the loading of a CV's grooves, the balls have a life expectancy that can't be exceeded.

Are we all dizzy yet?

Dave -- Dave Carpenter

Whatever you wish for me, May you have twice as much.

"Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering." -- Arthur C. Clarke


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