Date:         Sun, 5 Dec 2004 16:06:51 -0700
Reply-To:     Richard A Jones <jones@COLORADO.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Richard A Jones <jones@COLORADO.EDU>
Subject:      Ben McCafferty on CV joints
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I sent Ben a digest that mentioned his name
and the VolksCafe article that he wrote so
he'd know what's going on.  He doesn't read
the Vanagon list anymore.  He asked that I
post this for him:
-----------------------------------------------
Hello all,
Hope you are all well and having good adventures.  I have been riding
and working on my 1/2 VW (old BMW bike) a lot lately...

Regarding the CV article, this has always been a confusing topic on the
lists.  I should have been more clear in my article about what we're
trying to accomplish.  Reversing the direction of ROTATION of the CVs is
NOT the goal--rather, reversing the direction of the WEAR PATTERN on the
CVs is the goal.  In other words, the analogy someone mentioned where
the CD with an arrow on it is made to travel in the opposite direction
doesn't mean anything, because there are several moving parts at work
here, and simply having them travel the other direction (Iike rotating
tires L to R) doesn't necessarily do anything for the wear pattern of a CV.

The easiest way I can explain this is to have you pretend for a moment
that instead of outer hub, balls and inner hub, we only have the outer
hub and the inner hub--the balls connecting them are what generate the
wear, but it's easier to visualize this when you consider only these two
parts.  Take your hands and hold them with fingers pointed towards each
other and slightly apart.  Have each five fingers be in kind of a
circle, almost you're holding a baseball in each hand.  Now engage your
fingers with each other about a half inch or so to make a cage-like
structure, like you have your hand wrapped around a grapefruit with
fingertips overlapping.

Let's say your hands currently represent the left outer CV.  The right
hand is the axle/inner hub, and the left hand is the wheel/outer hub.
You are looking from the back of the vehicle to the front.  Since the
axle is driving the wheel forward, turn your right hand clockwise (top
away from you) and feel where the force is applied between your fingers.
  If you were looking at the back of your hands, you will feel force
(wear) on the right side of all fingers on both hands.

Now let's say that you rotated that axle in place, i.e wheel end to
tranny, tranny end to wheel.  The right outer CV is now the right inner
CV.  Kind of flip your hands over to mimic this flip.  You will quickly
realize that even though you have reversed the direction of rotation of
the CV, the left hand is now applying the force (because it's connected
to the tranny), and all force is still felt on the right side of the
fingers!!  So flipping the axle in place does not change which side of
the hubs is taking wear from the balls.

Now let's say that we are moving the left axle to the right side,
without flipping it over.  Remember that when the CV was on the left
outside, your right hand applied forward force to the left.  When you
shift the axle to the right side of the vehicle, the left hand is now
supplying forward force to the right hand, even though direction of
rotation is the same!  When you mimic this force with your hands, you
will immediately see that the force (wear) is now applied to the left
side of all fingers, not the right.  This is what we are trying to
accomplish!

Finally, let's look at the possibility of moving the left axle to the
right side, and also flipping it end-for-end.  In other words, the left
outer becomes right outer, and the left inner becomes the right inner.
As before, flip your hands over to mimic the new position of the CV
(right outer, with right hand being the inner hub, left being outer
hub).  Your right hand is now applying force to the left, but in the
opposite direction.  Here again, you will immediately feel that the
force (wear) is on the left side of all fingers, which is the desired
effect.

The main point of confusion for most people on this subject is the fact
that depending on BOTH a CV's location and direction of rotation, it
will impart force/wear to different faces, because of the fact that each
CV is made up of two parts working against the balls that connect them.

So going back to my article, the ways you can reverse wear on your CVs
and help extend their life are:

Starting with:
A---B  C---D

Switch to:
C---D  A---B

OR:
D---C  B---A

The following will NOT reverse wear:
B---A  D---C

By far the best things you can do for your CVs are to regularly inspect
boots and replace torn ones; and to inject fresh grease every 10,000
miles or so (or better yet, remove, clean and repack).  But when you're
in there anyway, this technique will help you get a lot more miles out
of them.

I hope this helps clarify the issue.  Feel free to email me personally
at ben@kbmc.net with any further questions.  Best regards to all...

bmc  :)
"Faith will move mountains, but you'd better bring a shovel...."