Motorcycle Suspension System Maintenance - Part 2
A fork seal is a part that must be replaced occasionally. It does a dirty, dusty, abrasive job, and eventually it just wears out. Fortunately, these seals are not very difficult to replace.
1. Remove the front wheel.
2. Remove the lower fork legs or sliders from the top tubes by taking off the retaining bolt, the attaching sleeve, or the circlip. Check your owner's manual to see which system your bike uses before removing the slider.
3. Protect the slider with a rag and put it in a vise. Gently pry the seals out of the top of the slider, being careful not to damage the delicate outer flange of the seal retaining area. A screwdriver works pretty well most of the time, but a pair of pliers may have to be used to remove the seal completely.
4. Clean the seal retainer area thoroughly with solvent then, after the solvent dries, apply a thin film of sealer.
5. Tap the new seal into place gently and evenly, using a large socket, pipe, or seal installer to keep the seal from pivoting as you drive it home. Be sure the sharp rubber lip is pointed downward so that fluid rising to meet it under pressure forces the lip up against the tube for a better seal.
6. Lubricate the seal lip with oil, then reassemble the forks. Be sure to fill the fork assembly with the correct amount and type of fork oil before riding the bike.
Spring Shock-Absorber Assemblies
As you know, when a motorcycle is traveling in level forward motion and the rear wheel strikes a bump, a spring-type shock is rapidly compressed. What you may not know is that the compressed spring will attempt to return to its normal length, so it will rapidly rebound, causing the rear of the motorcycle to be jarred upward. The first spring oscillation is followed by many others and contributes greatly to poor handling or outright loss of control of the motorcycle. A hydraulic dampening device is needed to control this oscillating action. Designers have met this problem by combining the spring and shock absorber, or dampener, into a single unit and that has been the state of the art for about half a century or so.
The shock absorbers used on the rear of most machines are similar to the front forks in design and operation. They also use hydraulic fluid, a dampening device consisting of a piston, valves, and seals to suspend and regulate the ride of the rear of the motorcycle.
In more or less conventional systems, the end of the shock is mounted to the frame while the other end is attached to the swing arm near the rear axle. When the spring is compressed or rebounds, its action is hindered by the shock absorber. So, instead of a long, dangerous series of uncontrolled oscillations, the spring action is smoothed out and the machine soon returns to its normal level. No matter if your rear suspension is conventional one per side, monoshock or whatever inventive scheme the engineers have designed, the essence of the functional parts are the same.