Before you even think about getting started on your
spring-wrapped wonders you need to set up an adequate workspace.
Lay all of your shock parts out on a clean rag, towel, or pit
mat. Using a sharp hobby knife, carefully trim all of the
plastic parts away from the parts tree. Make sure that you
remove all mold flashing, but be careful not to remove too much
material and alter the shape of vital components such as shock
pistons and shaft bushings.
Here are some tips that can be
used during most shock assemblies (follow your kit instructions
for specific assembly of your brand of shocks). Some shock
pistons attach to the shock shaft with a screw use motor spray
to clean this screw and the threads in the shock shaft and then
use blue or even red thread-lock to secure the piston. (I almost
never recommend red thread-lock in this hobby, but some shock
shafts need it to keep the pistons locked in. Check with your
manufacturer to see if they recommend permanent thread-lock for
their specific shocks.) Coat all of your o-rings and shaft
bushings in Green Slime,' which is available from Team
Associated (Part # ASC1105). This thick grease will help prevent
oil from leaking around your delicate seals. Always "wet"
your o-rings with a drop or two of shock oil before you push the
shaft through the seals at the base of your shock bodies to
prevent tearing an o-ring upon insertion.
QUICK FLUID LESSON
Why do some shocks have a bladder or a chunk of foam in them?
There are many different shock designs, but they all work
along the same principles. Fluid doesn't compress very much,
so once your shock shaft enters your shock body the
displacement of the shaft will eventually cause a hydraulic
lock. There must be some sort of volume compensation to take
up the slack from the non-compressing shock fluid to allow
your shock shaft to fully utilize its travel. Air molecules
are much less dense than fluid, so air compresses much more
easily. Emulsion shocks allow shock oil and air to mix
together to provide the volume compensation, but this can
cause less consistent results since air can pass through the
holes in your piston and produce erratic damping. That is
where the rubber bladders or closed-cell foam come into play.
The bladder or foam keeps air separated from your shock oil.
As the pressure builds within your shocks, the air within your
bladder or foam compresses and compensates for the extra
volume of your shock shaft. This allows your shock to utilize
its full range of motion. This pressurized air is also what
causes "rebound." When you push your shock shaft all
the way into the body it should push itself back out slightly
once you release the shaft. This is the pressurized air
releasing and forcing the piston and shock shaft back out in
the opposite direction. Rebound, or at least matching your
rebound is vital in building race winning shocks.
OIL IT UP
Once your shocks are fully assembled they are ready for oil.
This is the most important aspect when it comes to building the
perfect shocks, since matching them from left to right is a must
for maximum performance. Pour the same oil into both shock
bodies, then slowly pump the shock shaft and piston up and down
a few times to remove the trapped air from beneath the piston.
As you are pumping the shaft and piston you will see air bubbles
emerge from the piston holes and rise to the top of the oil.
Rotate the shock shaft as you are pumping to ensure that all air
is removed from beneath the piston. Once all of the air bubbles
have escaped from the oil you can top up the shock body with oil
and thread on the shock cap (different shocks assemble in
different ways, so check your specific instructions to find out
the manufacturer's tricks). Push the shock shaft in all the way
to make sure there isn't a hydraulic lock and also to check how
much and how fast the shock shaft pushes back out from within
the body. As already discussed, this action of the shaft being
forced out of the body is called the "rebound," and
this is what you are trying to match between shocks.
Once you are happy with the
rebound characteristics of the first shock your next job is to
match your other shock so it rebounds with the same speed and
distance as the completed one. Finish adding oil and threading
the cap onto the second shock and check the rebound. If you are
lucky it will be exactly the same as the first shock, but if it
isn't you will have to do some further tuning. If the shock you
are working on now rebounds faster and farther than the first
shock, you need to remove a tiny bit of oil. You can do this by
unthreading the shock cap slightly (a few turns) and pushing the
shock shaft in a little bit until a small amount of oil bleeds
out around the shock cap threads. Tighten the cap on again and
check the rebound. Continue with this procedure until both
shocks have equal amounts of rebound. If the shock you are
working on doesn't rebound as quickly or as much as the
completed shock, add some oil to it. Remove the shock cap and
place a few more small drops of oil into the shock body and go
through the verification process again. Continue adding or
bleeding oil from the shocks until they rebound at the same
If you can't get the speed and
rebound distance between the shocks to match regardless of the
amount of oil you add or bleed, you have a deeper problem such
as a binding shock shaft. You'll have to go back to the initial
building process to solve this problem before you attempt to
match rebound with oil again.
As a final pressurization check to ensure that your shocks are
completely matched with regards to shock oil volume and shaft
motion, hold a shock by the shock cap in each hand and butt the
two threaded ends of the shocks shafts against each other so
they travel along the same plain (just like one long shock shaft
with threads in the center). Use your hands to push the shocks
towards each other and force the shafts into the shock bodies.
Both shafts should move at the same rate, and they should both
bottom out within the shock bodies at exactly the same time.
When you pull the shocks away from each other both shock shafts
should rebound at the same speed to the same distance. If all of
this occurs, you have a matched set of shocks. If it doesn't. go
back to the start of this section and go through the process
With all this adding and bleeding oil out of your shock it's
going to get a little messy. The oil that you bleed out around
the cap will remain around the shock body and attract dirt once
installed on your car. After you've fully matched your shocks,
use some o-ring safe motor spray and give your shocks a quick
hit to remove any oily residue left from the building process.
This not only keeps them shiny and clean but allows them to
perform bind-free as well.
Now that you have your oil and rebound matched perfectly your
job isn't done yet. The physical length of your shocks must be
matched as well. Thread on your ball cups using the end of the
treads on your shock shaft for guidance. Use calipers to measure
the overall length of your shocks from mounting hole to mounting
hole and adjust the threading of the ball cup to match the
lengths perfectly from left to right.
Your springs are important when
it comes to building the ultimate shocks too. Most springs are
matched well, but some manufacturing processes can cause slight
tolerance differences. Use your trusty calipers to measure the
overall length of your shock springs and try to get a pair that
are exactly the same length. Use whatever measuring device you
prefer to check the preload spacing as well since this is easy
to mismatch, especially when using threaded shock bodies.
EVERYBODY PAIR UP
Always build and rebuild your shocks in pairs (as in left and
right shocks together). You will have a really hard time
matching your shocks if one of them is bound up from poorly
trimmed mold flashing or if one shock has fresh o-ring seals
while the other doesn't. If one shock is leaking and needs new
bushings and seals, replace the parts in the opposing shock as
well. If you get into the habit of wrenching on your shocks in
pairs you'll never have to worry about two mismatched tubes
filled with oil. [sb2]
Check the suspension components on your chassis to be sure they
are equally free of binding from left to right. Before
installing the perfect pair of shocks onto your chassis, do a
little investigative work to ensure it's ready. With the tires,
rims, and shocks removed from your car hold your suspension up
and allow it to drop. The suspension arm and assembly should
drop freely without any resistance. If it doesn't do this you
need to start shimming, removing shims, cleaning, reaming, or
grinding until it does. You also need to ensure that both the
left and right suspension movements feel similar so that when
you install your matched shocks the overall suspension works
equally from left to right. Once you know that everything is
acting the same, bolt on your shocks and go win some races.
By now you should have a strong understanding of how to build
your shocks to be smooth, free, and matched. However, it is
important to remember that your shocks will take a beating on
the race course, so constant attention is needed to keep them in
top performing order. Crashes, bends, and leaks can alter your
precise assembly work, so yank your shocks from your machine
from time to time and verify that they are still worthy to be
bolted onto your race car!