The Race Tech kit includes...
The Race Tech kit includes everything you'll need (except the oil.) You'll find parts and instructions required to lower the bike.
In 1935, BMW released the R12, a watershed motorcycle most notable because it was the first bike offered to the public equipped with a hydraulically damped, telescopic front fork. Despite the many advances in motorcycle technology over the ensuing 75 years, the fixed orifice/damper rod front fork has changed little; a technician familiar with BMW's seminal design would have little trouble working on any variation that's succeeded it.
This isn't necessarily a bad thing. Damper rod forks are inexpensive to produce, easy to maintain, and-so long as cutting edge suspension isn't required-work quite well, which is why so many motorcycles continue to use them. Unfortunately, they have one inherent flaw.
Following your shop manual's...
Following your shop manual's instructions remove everything in the way of the fork tubes. In this example - a Harley-Davidson Electra Glide-it's a little more involved than most.
In the simplest terms, fixed orifice dampers control the natural oscillations of fork springs by pumping oil through a series of small holes. Because it requires some energy to force the oil through the orifices, the springs' natural tendency to rebound uncontrollably after being compressed is reduced, or "damped," so the bike remains controllable (rather than turning into high-powered pogo stick as it would if damping were dependent solely on internal friction).
The major flaw with the design is that when fluid flows slowly through a hole, resistance to flow is very low, so there's little damping effect. However, as speed (meaning damper movement, not motorcycle road speed) increases, the oil's resistance to flow increases at the square of its velocity-move the oil twice as fast and you'll get four times the resistance.
Taken to an extreme, this "velocity squared" effect can cause the fork to behave as if damping is nonexistent at low speed, yet literally lock solid when some impact- a pothole, for example-forces it to move rapidly. For a simple visual of the phenomena at work, look no further than your most basic fixed orifice damper-the common screen door closer. Allow the door to close under its own weight and it'll move smoothly; try to slam it and the closer will lock solid.
In essence, while fixed-orifice forks can be made to work decently over a fairly wide range, they'll only work perfectly over a rather limited range. Their action and the amount of adjustability will always be limited by the size of the orifice.
 I like to remove the damper...  I like to remove the damper rod-retaining bolt while the fork is still assembled; that way the fork spring holds tension on the rod to prevent it from turning. A 1/2 inch impact driver should spin most of them right out with no drama. In some cases once the bolt is out, the lower leg will drop straight off, so be ready if that's how your fork is designed. |  Loosen the upper and lower...  Loosen the upper and lower pinch bolts and slide the tubes out of the triple clamp. In most instances they'll drop right out but in some cases there may be rust seized into the clamps. Liberal applications of rust-penetrating oil and a few light blows with a plastic mallet should get things moving. In some instances, you may need to insert a wedge in the split section of the clamp. | |
The Solution
Suspension technology has always lagged behind engine development, and by the late seventies suspension shortcomings were becoming a real problem, particularly on the racetrack. The solution that suggested itself was to vary the size of the damper orifice in response to the speed of the oil passing through. That way you could create suspension that was linear in action; supple and firm at low and moderate velocity, yet free from potential lockup at the highest (damper) speed. That's precisely what the cartridge fork, which arrived in the mid-Eighties, does.
The cartridge fork does away with the damping rod and its drilled holes, replacing them with a cartridge tube and speed-sensitive valves or pistons. Although I don't have room for a full explanation here (partly because each manufacturer has their own design), the short version is that pistons can adjust their orifice size quickly in response to oil pressure, and as such are able to deal with both large and small hits in a proportional manner. This makes suspension action smooth and progressive, and because valves are almost infinitely adjustable, suspension characteristics can be tailored to the individual rider's needs.
While the cartridge fork is undeniably a better device than the fixed orifice type, it does have a drawback: cost. Cartridge forks are more expensive to build than an orifice-damped fork so manufacturers have to charge more for bikes equipped with them. That's why they're more often found on machines that require premium suspension units, like high-end sport bikes and motocrossers, than on things like cruisers and standards.