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by Mike C. -
Wheel Shimmy – I
There is perhaps nothing much more aggravating than
out-of-balance wheels on your VW. The entire car may look like a million
bucks and the engine may be the fastest thing on the planet, but if your
wheels are out of balance, it will ruin the whole driving experience.
Beetles with their lightweight front ends are particularly susceptible to
imbalance and Super Beetles are notorious for making owners pull their hair
out and eventually give up. I’m here to tell you that it doesn’t have to be
that way, and even Super Beetle owners can have a smoothie and you can keep
your hair in as well. I won’t go through the step-by-step procedure as far
as the actual balancing goes since most folks don’t have the equipment
(sometimes very expensive) to properly balance the tire/wheel assembly, but
I will list the causes and solutions to each problem the best way I know
how. I will be focusing on the old air-cooled VW’s but you can apply much of
the theory to all cars out there.
Rotating Assembly
I’ll start by talking about your rotating assembly. This
simply means the tire/wheel combo and the brake rotor and/or drum. After
all, if something isn’t right about them, they will transmit that problem
all the way through, no matter the condition of the rest of the suspension.
- Drums & Rotors -
Begin by making sure your drums and rotors are
straight. I mean, take the wheels off and mount a dial indicator to
something solid, position the indicator contact point on the surface where
the wheel actually mounts (don’t put the contact point in-line with the
lug bolt holes) and rotate the disc or drum. You ideally don’t want any
needle movement (called runout) on the dial indicator. You probably will
though, and limit this runout to 0.002" inch. This may not sound like
much, but 0.002" will become a lot bigger number by the time you get to
the outer edge of the tire when it is mounted on the car. If you have more
than 0.002", take the disc or drum to a machine shop that has a lathe and
they can get this surface true. You may even be able to get your
automotive brake shop to do this for you. Do this for all the discs and/or
rotors.
Wheels -
Now turn to the tire/wheel assembly. Mount them back on
the freshly-machined brake discs or drums. Spin them and watch to see if
the rims are bent. You can take the dial indicator and do the same thing
you did with the brake drums, only make sure you don’t scratch the rim
with the indicator contact. Make sure you measure at the outer edge of the
rim. Again, I don’t like to see any runout here (no more than 0.002" to
0.003"). If you didn’t use a dial indicator, watch carefully. If you can
visually see that the rim is bent (wobbling side-to-side) then that is too
much. Don’t let the motion of the tire fool you. If the rim appears to be
going up and down (radial runout), then either the holes in the rim were
drilled off-center, the holes in the brake drum were drilled off-center,
or in the case of an aluminum rim the tire mounting surface may have been
incorrectly machined. Most likely, this type of runout is caused by the
lug holes in the brake drum being off-center. There isn’t much you can do
about radial runout except to try different drums or rims. Whenever
possible, try to stick with German brake drums or rotors, as the Brazilian
and Mexican-made units tend to be of much poorer quality. I went through
this before, and have seen as much as 0.010" or more runout in these
parts. Aluminum rims are far less likely to be out-of-true than steel
rims, as the aluminum rims are machined to size. Again, beware of the
steel rims, as you can’t get new original-style steel wheels from der
Motherland anymore. There are shops dedicated to building and
straightening steel wheels, but there are none locally that I’m aware of.
- Tires -
Tires are the last things between the road and you, so
runout is critical in these, too. You check these while checking the
wheels, and in the same way. The tires ideally should have no runout, both
lateral (side-to-side) and radial (up and down). You’ll have to do a
visual check to verify this, as a dial indicator would not work well on a
tire. Again, if you see the runout, it’s too much. All you can really do
with tires is make sure you buy a reputable name brand if possible, like
B.F. Goodrich, Goodyear, or Michelin. If you are sticking with stock
165SR-15’s, you won’t likely find them in any of these brand names. Just
ask around with fellow VW owners about what they are using and go with
your gut. You can see from what you have to do with the possible problems
of all rotating components that all the runout problems could "stack up"
and cause big problems that you’ll never solve with mere balancing. In
fact, if your rotating assemblies are free of runout, you can get by with
a lot more suspension wear since a worn suspension will actually magnify
runout problems with wheels and tires.
We’ll finish up our balancing act next month with
suspension and tire balancing.
Your VW Maniac &Tech Specialist,
Mike C.
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