Brooks:
U Joints have an interesting property: When the input and output
are collinear (i.e. perfectly aligned) input velocity equals output
velocity. When there is misalignment (due to suspension compression,
frame flex, engine torque on the motor mounts, etc), input velocity DOES
NOT equal output velocity.
A misaligned U joint will cause the output to speed up and then
slow down at a multiple of the rotational velocity (2x, I think). This
can be countered by installing ANOTHER U joint, which will cancel the
changes in velocity. If the two U joints are misaligned relative to each
other, you will get some pretty good vibrations going as they will
"fight" each other. This cannot be cured by balancing and will continue
forever unless both joints are perfectly aligned (which in practice is
impossible to achieve). This is because the shaft between the two U
joints will rapidly wind up and then unwind (like a torsion bar)
delivering some strong harmonics to the drive line which is very
noticeable, not to mention hard on bearings and what not.
One engineering solution to this is the constant velocity joint
(CV) which is of a different construction and which delivers, you
guessed it, a constant output velocity when misaligned. These are used
in FWD vehicles because U joints result in objectionable vibration when
turning. As you also probably guessed, they are bulkier and more
expensive and therefore are only used where necessary.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@Autox.Team.Net [mailto:owner-6pack@Autox.Team.Net] On
Behalf Of Brooks Bullock
Sent: May 16, 2007 8:41 PM
To: 6-Pack List Serve
Subject: RE: [6pack] Vibration
Rick,
I haven't seen anyone mention this but if the Drive shaft splines were
separated to ease the U-joint install, I suggest making sure the front
yoke
lines up with the rear yoke +)---------(+ maybe this is what Dick was
refering to as mismatched flanges? I recently did this and even knew
better, I'm sure someone can better explain why it sets up some kind of
harmonic vibe.
good luck
Brooks
CF28658UO
CF51243U+O
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