a lot of technical improvements have been made in ride control
technology in recent years, the replacement market for shocks and
struts has remained relatively static. The economy has had a lot to do
with the sluggish sales, but other factors are equally to blame. One
reason shocks and struts are not flying off store shelves is because
many technicians don’t take the time to inspect these parts when doing
alignments, brake work, oil changes or other undercar repairs. If
nobody tells the vehicle owner that his shocks are weak or worn out,
chances are the customer may not realize how much the ride control
characteristics of his vehicle have changed since it was new.
are generally uneducated about the impact poor ride control can have on
braking, handling, traction, tire wear and driving safety. Most
consumers still think ride comfort (or lack thereof) is the only reason
why shocks or struts might have to be replaced. That’s why one
aftermarket shock manufacturer has been recommending the replacement of
the shocks and struts every 50,000 miles. By suggesting a specific
mileage interval for replacing the original equipment dampers, it sends
a message to consumers (and technicians) that shocks and struts do not
last forever, and eventually should be replaced to restore like-new
ride quality and control.
control is especially important with today’s high-tech antilock brake
and stability control systems, as well as electronic suspensions and
self-leveling suspensions. Stability control systems, in particular,
are calibrated to work with the spring rates and dampening
characteristics that were engineered into the vehicle. If the shocks or
struts are weak and providing poor control, and/or the springs are weak
or sagging, the stability control system may not be able to control the
vehicle with the same degree of effectiveness as when these parts were
rear shocks, for example, can allow a lot more wheel bounce when
braking hard on a rough road. If the tires are losing contact with the
road, it may trip the antilock brake system unnecessarily. When making
a sudden steering maneuver, excessive body roll or suspension motion
could affect the ability of the stability control system from limiting
understeer or oversteer by counterbraking. So with today’s high-tech
systems, weak shocks and struts can affect a lot more than ride comfort.
ELECTRONIC RIDE CONTROL
suspensions have been around for nearly two decades, and include
everything from electronically adjustable dampers to self-leveling and
adjustable ride height systems. Some of the more sophisticated
applications combine variable dampening rates with variable rate air
springs to optimize handling, ride comfort and cornering agility. The
body control computer monitors vehicle speed, steering angle and
G-forces, and in some cases, suspension movement to vary the ride
control characteristics of the suspension. The shocks and struts may
have an internal solenoid valve or electric motor that repositions the
valving to vary the resistance of the dampers. On other applications,
the shock may contain a special magnetorheological fluid that changes
viscosity (thickness) when exposed to a magnetic field created by a
small coil inside the shock.
high-tech electronic shocks and struts can provide both a smooth ride
and firm handling when everything is working correctly. But like
ordinary hydraulic shocks and struts, they eventually wear out or fail
electronically. And when they reach the end of the road, they can be
VERY expensive to replace. We’re talking hundreds of dollars apiece for
many of these parts.
can also be an issue if a vehicle is more than about 10 years old. Many
new car dealers do not stock parts for older vehicles because the
vehicle manufacturer has discontinued the parts. Fortunately, this
creates a tremendous sales opportunity for the aftermarket because
replacement shocks and struts are available for many of these
applications, including much lower cost conventional replacement shocks
and struts. Obviously, replacing a set of high-tech electronic shocks
with conventional shocks will disable the electronic ride control
system. But for owners of older vehicles who can’t afford the repairs,
it is a cost-saving option that may be considered.
same goes for many air-ride and air-assisted, self-leveling
suspensions. Leaks are always a problem with air suspensions of any
type. Air springs can leak. Air lines can leak. Fittings and
connections can leak. What usually happens when a leak develops is that
the compressor runs continuously in an attempt to overcome the loss of
air pressure. These little compressors are not designed to run
continuously, so eventually they overheat, burn up and fail. Now the
repair requires not only new shocks, air lines and/or air springs, but
also a new compressor. The cost to repair the system may be more than
an older vehicle is worth. So the vehicle owner has a tough decision to
make: to spend the money, to look for a less expensive solution to his
problem, or to junk the vehicle.
Lincolns and Cadillacs with air-spring suspensions are notorious for
failing and going flat. They can also cost a small fortune to fix
unless the original air-spring struts are replaced with conventional
metal springs and struts. The latter cost much less than the original
equipment parts, yet provide a satisfactory ride without all the
complication and potential for more expensive repairs down the road.
high-tech shock to be aware of is the self-leveling Nivomat monotube
shocks made by ZF Sachs. They are used on the rear suspensions of some
2004 and newer vehicles such as Chrysler minivans and Pacifica, Chevy
Suburban and Tahoe, Cadillac CTS as well as other Ford, Jaguar, Kia,
Mitsubishi, Saab and Volvo models. Unlike other self-leveling
suspensions that use air bladders, air lines and compressors to
maintain ride height, Nivomat shocks use an internal accumulator, pump
and valving to maintain a predetermined ride height as the vehicle load
changes. The shocks can also adjust their dampening characteristics to
changing driving conditions, too.
Nivomat shocks are calibrated for specific vehicle applications, as are
the rear springs (which are usually softer because the shock also
supports a portion of the vehicle’s weight). Because of this, most
vehicle manufacturers say a worn or defective Nivomat shock should be
replaced with the same not a conventional shock. Even so, aftermarket
shock suppliers have come out with less expensive conventional
replacement shocks for many of these applications. They obviously can’t
provide the self-leveling feature, but for the difference in price many
motorist can live without it.
of the best ways to sell ride control products is to sell ride control
performance upgrades. Though this market segment is limited primarily
to sport and performance vehicles, and off-road trucks, the bright side
is that some vehicle owners will replace relatively low-mileage stock
parts, even brand new parts, with aftermarket performance parts. They
won’t wait for the original parts to wear out because they want
enhanced ride control NOW and will even pay premium prices for
top-of-the-line performance parts.
includes high-pressure monotube shocks as well as coil-over conversion
kits, and even complete suspension handling kits that include shorter
stiffer springs, sway bars and bushings. The best results are often
obtained by going with a totally engineered suspension package rather
than mixing and matching parts from different suppliers.
shocks and struts (either manual or electronic) provide the best of
both worlds: everyday driving comfort with soft settings to firm ride
control with stiffer settings. A common mistake that some driving
enthusiasts make is to have a track suspension installed on a street
car. I recently bought a used 2008 Mustang GT that somebody had fitted
with a set of Steeda brand performance shocks. On a smooth road, the
car handled and cornered like a go-cart, and could keep up with nearly
any Corvette. But on potholed and patched urban streets or washboard
and tar strip covered highways, the car rode like a pogo stick and felt
like it would jolt the fillings out of my teeth. What works great on
the track is often not the best choice for the street.
what did I do? I removed a set of perfectly good, low-mileage
ultra-stiff performance shocks (which probably cost upward of $400 a
pair new) and replaced them with a some smooth riding gas-charged
aftermarket shocks. The difference in ride quality was immediate and
dramatically more practical for a daily driver, yet there was little,
if any, noticeable sacrifice in cornering agility or handling. The car
still handles great but is much less harsh to drive. So if you are
selling performance shocks to a customer, make sure you find out what
kind of driving they do (and not just on weekends, but all week long).
Then, recommend a set of shocks or struts that best matches the
many, that would be some type of monotube high-pressure gas-charged
shock or strut, preferably adjustable if the vehicle is a dual purpose
daily driver. These are available from various aftermarket suppliers,
as are spring and performance suspension handling kits.
TYPES OF SHOCKS
a conventional twin-tube shock absorber, an outer tube that acts as the
fluid reservoir surrounds the inner piston chamber. As the shock pumps
up and down, the action of the piston forces the hydraulic oil inside
to flow back and forth through valving in the bottom of the shock into
the outer fluid reservoir. In a monotube shock, there is no outer fluid
reservoir. All the fluid remains in the piston chamber, and a floating
piston separates the fluid from a high-pressure gas charge.
the piston moves down, the fluid pushes against the floating piston and
compresses the gas charge underneath it. The gas is actually nitrogen
(air with oxygen and moisture removed). This creates a sort of “air
spring” effect that keeps the fluid under constant pressure to reduce
foaming as it flows back and forth through the orifices and valves in
the monotube design to work, the gas pressure under the floating piston
in the bottom of the shock must be quite high: typically 260 PSI or
higher. This also requires a good seal on the floating piston and a
highly polished surface inside the piston tube both of which increase
the manufacturing cost of the shock.
the monotube design was invented back in the 1950s, it was a
revolutionary breakthrough in shock absorber technology. The floating
piston and high-pressure gas charge solved the foaming problem that had
plagued conventional hydraulic shocks for a long time. When the fluid
foams, the tiny bubbles offer less resistance to the motions of the
piston causing the dampening characteristics of the shock to fade. This
allows more wheel bounce and suspension motion and hurts handling. So
when the first monotube gas charged shocks came out, it made a dramatic
improvement in handling control.
shocks were widely used in racing in the 1960s and 1970s, and found
their way into NASCAR in the 1980s. Since then, monotube shocks have
also been used as original equipment on a variety of cars including
Mercedes, Audi, Porsche, BMW, Saab and Volvo, 1993 and newer Camaro and
Firebird, late model Corvettes, and even some pickup trucks.
addition to reducing fluid foaming for better ride control (which is
the gas-charged monotube shocks main advantage), the design has
additional advantages over a conventional twin-tube shock:
The monotube shock provides better heat dissipation and cooling than a
twin-tube shock. There is no outer tube or fluid reservoir to inhibit
heat flow, so the monotube shock runs cooler and delivers more
consistent ride control.
A monotube shock is lighter than a twin-tube shock that has the same
external diameter. This reduces unsprung weight and allows the wheels
and tires to follow the road more closely.
A monotube shock can be mounted in any position (right side up, upside
down or even sideways) and still work. A twin-tube shock uses gravity
to drain the fluid down through the valving in the bottom, and maintain
the gas charge in the outer reservoir. But a monotube has a floating
piston and no reservoir, so the orientation of the shock does not
matter. On racing applications such as Formula One or Indy Cars, the
shocks can be mounted sideways inside the body to reduce drag for
A monotube shock has a larger diameter piston than a twin-tube shock
that has the same external dimensions, which gives the shock greater
sensitivity for small piston motions.
of what type of dampers may be used on a vehicle as original equipment,
or as aftermarket replacements, shocks and struts should be inspected
periodically to make sure they are not leaking, damaged or worn out.
Fluid leaks occur if the piston shaft seal is worn. Sooner or later, a
leaky shock will lose enough fluid to reduce its dampening ability.
leaks are harder to see, but if a piston is leaking fluid, chances are
it has probably lost its gas charge, too, reducing its ability to
prevent foaming when the shock is working hard. This leads to shock
fade and loss of ride control.
bounce test is still a valid means of identifying weak dampers. Rock
the suspension several times up and down, then release it. If the
dampers don’t stop the motion within once bounce, the shocks are weak
and should be replaced to restore like-new ride control.
symptoms of worn shocks include suspension bottoming after hitting a
bump, excessive nose dive when braking, excessive body lean or sway
when cornering, a bouncy or undulating ride, wheel shudder or shimmy
after hitting a bump and cupped tire wear.
shocks and struts should always be replaced in pairs (both fronts, both
rears or all four) to maintain even ride control. Other suspension
parts such as the springs, bushings, ball joints and steering linkage
also should be inspected for worn, loose or damaged parts.