Rod & Custom

11
Wheel Centerline
Trail
Caster Angle
We amplified the dimensions but this illustrates
how the tire centerline (yellow) actually “trails”
the point where the steering axis (red) intersects
the ground. Less trail makes a car feel lively but
too little makes it wander. More trail makes it
stable but too much makes the steering feel dead
and can induce a wobble.
front on a rear-drive car—encounter
an intense amount of resistance.
Just one worn component can
let the suspension deflect out of
alignment. If the suspension deflects
enough to let the geometry enter an
unfavorable range then a wobble
may follow.
DRIVESHAFTS
Last but far from least,
driveshafts, since they spin several
times faster than the drive wheels
they’re particularly capable of
vibrating. We’ll let Steve Raymond
at Dynotech Engineering Services
explain a few essential things.
And he’s well versed; when the
Big Three encounter persistent
vibration issues they hire Dynotech
to find and solve them.
“You want equal and opposite,”
he instructs. “If your tailshaft
points down 2 degrees then your
pinion should point up 2 degrees
so effectively they run parallel.”
Why? Universal joints at an angle
don’t spin in a circle; they follow
an ellipse that makes them speed
up and slow down at various
points. “If the joints are phased
correctly on the shaft then one joint
will accelerate as the other joint
decelerates and the two forces will
cancel each other.
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Consider every wear point a potential culprit in a
persistent wobble issue. Worn kingpins, ball joints,
bushings, tie-rod ends, idler arms, strut rods, and
even steering gears can let the geometry slip into
the wobble zone.
DRIVESHAFT ALIGNMENT
Best
Poor
Bad
Worst
But don’t confuse parallel with
straight line. “Set your U-joint
angles at a minimum of 0.5 degree
to 3 degrees,” he says. “If the joint
is at 0 degrees then (it) won’t
articulate and the needle bearings
won’t roll. That will purge the
grease out of the caps and wear the
bearings. But when they roll they
distribute grease through the cap.
Without that little bit of movement
the joints will run hot and wear
out prematurely. A worn joint can
introduce a vibration.”
Here’s a tip if your engine
vibrates at certain speeds even
when the car sits still: disassemble
assemblies (like a torque converter
from a flexplate), rotate one
side (like the torque converter),
and reassemble. You may do a
reasonable job balancing each
of the components but small
imbalances always remain,” he
says. “So you have to prevent those
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Parts
THE WHEELSMITH
(800) 854-8937
www.thewheelsmith.net
This is a steering
damper. Though
it can damp small
oscillations that cause
wobbles that is not
its job. It exists to
take the edge off
of the small impacts
amplified by the gear
lash in older steering
boxes before they
reach your hands.
Yokes within 0.5 to 3
degrees of shaft. Parallel
yoke centerlines.
Zero joint angle. Caps can’t
rotate to distribute grease.
Yoke angles greater than
3 degrees of shaft wears
joints prematurely.
Non-parallel yoke
centerlines induce vibration.
Joints work best with at least 0.5 degree but no more than 3 degrees misalignment. For a one-piece
driveshaft on a road car set the pinion angle at the exact inverse angle of the tailshaft. So if the
tailshaft points down 2 degrees then point the pinion up 2 degrees.
DYNOTECH ENGINEERING
(800) 633-5559
www.dynotechengineering.com
INNOVATIVE BALANCING
(866) 352-7251
www.innovativebalancing.com
COKER TIRE
(423) 265-6368
www.cokertire.com
BUFFALO ENTERPRISES
(360) 652-7684
www.inliners.org/buffalo
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small imbalances from adding up
at one angle.” By rotating one part
180 degrees the imbalances may
cancel out each other.
58 rodandcustommagazine.com