The rod ends can become loose...
The rod ends can become loose or tight. With excessive wear, they become loose and with corrosion or dirt infusion, they become tight. Neither of these conditions are good. All suspension components must be free to move without any amount of friction.
Maintenance involves an evaluation as covered above, replacement of the shock oil, and replacement of all of the O-rings and seals. We also need to replace the Schrader valve each time we have the shock apart, too. This is a fairly inexpensive part, but if it leaks, can change the characteristics of the shock and cause problems that are hard to detect.
Be sure to clean all of the parts thoroughly, especially the bleed holes that can be quite small in diameter. Debris and burned oil can become lodged in these small holes affecting the low speed control of the shock.
The hard parts such as the shock shaft, piston, body, and end caps are usually good to go for a long time if not damaged. But, the end Heims should be looked at closely for wear which will make them loose or corrosion which will make them tight. If the Heim housing is a part of the end cap, then that cap might need to be replaced. The Heim at the end of the shock rod is most easy to replace.
The O-ring seal in the end...
The O-ring seal in the end cap must be knick free and remain pliable. Use a new ring every time you rebuild and coat it, and all seals, with shock oil before installation. Don't install dry seals.
FUTURE NEEDS When we have the shock apart, we need to think about the direction we have come from and where we are going with our setups. Then we can plan out shock changes and incorporate those changes into our newly rebuilt shocks. The type of piston, the degree of preload, the valving and preload all need to be looked at in relation to our future setups.
Shock pistons come in various preload shapes. That means one or both sides can be designed to be of a digressive or linear flow and/or dished to a varying degree to add preload to the valve discs. To add preload, the discs are bent against the piston face into a dish shape when the assembly is tightened down. It then takes more pressure against the valve discs before they will open. This is called "head" or "nose" because it takes a higher hydraulic head force to open the flow of oil through the piston.
The pistons come in various flow characteristics such as Linear and Digressive with preload in 1-5 degrees of dish on one or both sides of the piston affecting compression and/or rebound. You can also regulate the slow speed control by varying the size and number of bleed holes.
Note the small hole in the...
Note the small hole in the side of the piston just above the black seal and just under the nut. This hole is the slow speed bleed. Shock oil can bleed or flow past the valves at low shock speeds which correspond to low internal oil pressures. Once the speed of the piston increases and the pressure increases, the valves will open and the slow speed bleed hole becomes less affective.
Bleed holes allow the flow of oil from one side of the piston to the other before the pressures build that will allow the piston valves to open. The faster a shock and piston moves, the greater pressure is exerted on the valves. At some point, they will open and allow the oil to flow through the piston. Until then, the bleed holes control the movement of the shock at low speeds.
TECH HELP It's critical that you understand the operation of the shock and how the various components affect the dynamics of the shock. Read up on shock technology; call your shock supplier and/or manufacturer's tech people to inquire about your particular racing needs and how you can improve your setup with different shocks.
Be especially aware that making changes in the setup will necessarily change the way the shocks affect the handling of your car. Spring changes might be a positive way to go, but not fully realized if the shocks are holding you back.
CONCLUSION As with many other race car component maintenances and selections, it's of great importance that you consult your favorite manufacturer's tech people when designing your system, replacing parts, or having a problem that is shock related.
The people I've talked with and who advise us with our project cars and articles are a wonderful resource and they talk with hundreds of racers a year. Their level of knowledge goes far beyond any of ours because this is their business. They walk and talk shocks whereas we have to think more broadly about our race cars. They can also make you aware of new processes, new parts, and better shock developments that will coincide with the current trends.