Motorcycle Suspension System Maintenance - Part 3
Spring / Shock Details
The telescopic shock absorber has an inner cylinder, an outer cylinder, piston, piston rod, spring mounts, and sometimes dust covers. In addition, a series of valves, passages, and seals control the flow of hydraulic fluid inside the shock absorber. When the bike is at rest or at normal loaded height, the inner cylinder is completely filled with fluid, while the outer cylinder is only partly filled. The piston is near the midpoint of its travel to allow movement in both up and down directions.
Shock action during compression changes the fluid balance so that the piston and rod have been forced down in the pressure tube. If the piston is to travel downward, the fluid must press through the piston valve into the upper section of the pressure tube. As the piston descends, some fluid is forced through the base valve into the reservoir tube. Shock absorber valves are calibrated to cause a certain resistance to the passage of fluid. They permit slow, smooth spring action, but resist or cushion violent spring oscillation.
In the shock action during rebound, the piston is forced upward in the pressure tube, and the fluid trapped above is moving down through the piston by way of a different valve. Shock action on rebound is similar to that on compression. Some shock absorbers are calibrated to provide more resistance on rebound than on compression. Others may be custom calibrated by changing washers or by adjusting spring rates.
Spring / Shock Service
Most shock absorbers are mounted by means of rubber grommets on studs that extend from the swing arm and frame. Some rubber lubricant, brake fluid, or soapy water can ease the installation of tight new shock grommets when replacing them.
When riding with a passenger or carrying a significant load, you should compensate for the extra weight by stiffening the rear springs. This simple adjustment is accomplished by turning the spring retainer base a notch or two to shorten the spring. The number of positions for adjustment vary with the make of machine, so you should experiment to determine how much to adjust the springs for various weight loads on your machine. Should you need more or less spring rate than is available from the range of adjustment on your shocks, replacement springs or spring/shock units are available to meet nearly every conceivable need.
The stout swing arm(s) found on today's motorcycles require almost no maintenance themselves, but place great demands on its bushings, which pivot on a cross shaft at the bottom of the frame. These swing-arm bushings should be lubricated periodically and inspected for looseness. There should be almost no detectable lateral movement when you try to move the swing arm sideways. If there is excessive movement, order a new set of swing-arm bushings and replace them, using the following sequence:
1. Remove the rear wheel.
2. Disconnect the lower shock mounts and the chain guard if necessary.
3. Remove the swing-arm pivot shaft by using a drift.
4. Clean the swing-arm bushing area with a solvent.
5. Drift out the old bushings.
6. Press or carefully tap in the new bushings, being sure to align the grease holes if they are present.
7. Ream or hone the bushings to a proper fit if necessary.
8. Lubricate the shaft and reinstall it. Use a mallet or press it in with a clamp or hydraulic press.
9. Reinstall the wheel, shocks, chain guard, etc.