Shock maintenance means evaluating...
Shock maintenance means evaluating and maintaining all of the parts and pieces of the racing shock. Replacement of all seals and O-rings is wise. Let's take a more holistic approach to shock maintenance.
Shock maintenance should not be left to the end of the season, but often that's the case. Now that we have a chance to take a deep breath and look over all our systems, it's a good time to do an assessment of our shock needs and what kind of maintenance we need to do to improve on performance.
Shocks are, at best, a tuning tool and many teams have taken this a little too far and asked the shock to act as a manipulative device. We see teams trying to "tie-down" the left front corner or the left rear of the car. The only way to tie the left front to the track is to bolt the tire to the asphalt, and we know that's impossible. All we are doing when we restrict the rebound movement of the suspension is to lock that suspension solid. Load will still transfer from the left side to the right in the turns, but the left suspension will not move.
Many think this lack of movement means no load is transferring, but like a racing kart, load does transfer and in much larger quantities than if the suspension were allowed to work. The benefits of that methodology are hard to quantify. Nonetheless, whatever shocks you run, you still need to maintain them. Here are some ideas for selection of shocks and how to evaluate the efficiency and rebuilding of racing shocks.
Dings on the outside of the...
Dings on the outside of the shock body can have a reshaping effect on the inside wall. Any time your shock takes a lick and shows a dent, remove and take the shock apart and inspect the inside wall.
EVALUATION We first want to evaluate how our shocks performed during the past season. Are they doing the same work now as when they were installed some 10 months ago? Did our setup change as the season progressed and did we keep up with those changes by modifying our shocks? Did we have failures in our shock package and what can we do to prevent failures in the future?
Go over your notes and see what shock settings you ran throughout the season. Make notes based on the chronology, or timeline, of events to see trends in the changes you made. Note any failures of any one shock and the corner that was affected.
If your basic setup changed during the season, note how it changed and what, if any, changes were made to the shock package. If no changes were made, now is the time to re-evaluate your package to better enhance the newer setups.
We know for a fact that the same shock package can't work for both conventional setups and BBSS setups. Simple shock technology tells us that the springs resist compression and promote rebound. So, the shocks must change in their compression and rebound rates to compensate for spring rate changes.
This is the same shock body...
This is the same shock body showing how the dent on the outside transferred a bulge to the inside wall. This could affect the motion of the piston.
A higher spring rate at one corner will necessitate a higher amount of rebound control and less compression control to keep the same motion characteristics. Many professional teams from the NASCAR Truck series up to the Cup level use fixtures where they can install the spring and shock in the true motion ratios used in the car to rate the combination of springs and shocks. This method gives us a true picture of compression and rebound related to the wheel.
INSPECTION OF EXTERIOR An outside visual inspection is necessary to determine if any damage has been done to the shock. For sealed shocks, we will not be able to inspect the inside, but we can have them dyno'd and inspected by a factory authorized tech center or the manufacturer.
If you're using adjustable shocks, note and record the settings before you go any further. These are the settings you ended up with and probably will start with next season. Don't forget to write down what you have. Once you start the maintenance part, these settings could end up being changed.
The spring caps support the...
The spring caps support the load of that corner of the car. Make sure they are in good shape and not worn excessively or cracked. These are just the kind of cheap, replaceable parts that can ruin your race day.
In the case of a sealed shock, it's always a good idea to send the shocks to the tech center for evaluation, dyno-ing and/or rebuilding or replacement. In this case, maintenance by the team is not a choice and all we can really do is hand cycle the shock and look and feel for obvious damage externally.
If you have user-serviceable shocks, then read on, and we'll tell you how to proceed with your maintenance. This still means you should visually inspect the exterior of your shocks before disassembly.
Look for obvious leaks, shaft damage such as a bent shaft, scratches, or scoring. A discolored shaft is a sign that the internal temperatures are too high and the oil may be burned. Nicks and dents on the outside of the shock body may have carried through to the inside walls of the shock restricting movement of the piston.
Inspect the rod ends for corrosion, excess wear, and damage such as dings and cracks. If a shock was bent in a collision during the season, many teams will remove and reuse the rod ends. They might have missed damage in the heat of the moment. Now, we can take time to do a thorough inspection after the ends have been cleaned.
Before you disassemble your...
Before you disassemble your adjustable shocks, record the settings. You will want to return them to the positions where you left off last season. Turn the compression adjuster to the right and count the clicks to full lock. Then write that down. For the rebound adjuster, move the wheel from left to right facing the shock with the rod end down. Again, count the clicks to full lock and record.
Cycle each shock by hand. Place the shaft end of the shock on the floor and push the shock in or down and note the resistance. This gives somewhat of an indication of its condition. Feel for spots where the shock movement is easier or harder. This indicates a bent shaft or scored inside wall. Clamp the shaft end and pull on the shock in the same way.
Gurgling sounds and skipping are signs of cavitation and indicate that gas may have mixed with the shock fluid, or the seal separating the compression fluid from the rebound fluid has leaked or worn out. I've had shocks that were either very easy to move or solid and did not move. Amazingly, the driver could not tell us that the shock was stuck.
Once you have carefully inspected the exterior, we can disassemble the shock and evaluate the interior parts. Look over the threads that are a part of coilover shocks for height adjustment. These can be repaired if they are dinged or worn by filing. The adjuster ring should spin freely with no sticking anywhere along the range of motion you will be using. A light lubrication can be applied later.
INSPECTION OF INTERIOR As we disassemble the shock, we'll see the shock oil first. Note the color and texture of the oil. If it has endured high heat and been used too long, it will appear dark and smell somewhat burnt. Strain the oil to look for material that may indicate a decomposing seal or broken parts.
This shock cap has been rubbing...
This shock cap has been rubbing on the frame or shock mount. This can have a huge affect on the motion of the suspension. Conflicts such as these can ruin an otherwise great setup and will be very hard to find. Look over your installation when mounting the shocks onto the car. They should not make contact with anything on the car in a full range of motion of the suspension. The cap shown made hard contact and that definitely affected the car's handling.
Note the condition of the shaft seals along with the O-rings around the piston and the piston seal. With gas pressure shocks, the floating separator piston needs the same inspection.
Look at the valve discs and see if they are still sealing well. Inspect the inside wall of the shock body and look for inward facing dents and/or scratches. The wall should be pristine in appearance or the shock body will need replacement.
Once the piston/valve assembly has been disassembled, look at the valve discs. Sometimes these will have burned oil caked on them in the pattern of the piston and will need to be replaced. The chance that they could be reassembled in exactly the same position is a long shot at best. If not positioned correctly, they would leak and affect the overall shock operation.
MAINTENANCE Shock maintenance is a process that depends mostly on the extent of use. A team that races 20 races a year will get by with annual maintenance. If you run a more southern schedule of 30 or more races a year, with a few touring races thrown in, you'll need to do maintenance twice or three times a year.
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.
This shock oil can reach high temperatures on some tracks and actually burn into the shock valve discs. Note the discoloration of this disc in the shape of the piston.
The seal for the shaft can become scored and torn from heavy use and having to scrape dirt and grime off of the shaft as it moves in and out. This seal will need replacement often, especially in a dirt track environment.
This is the piston seal that lies just outside the O-ring around the piston. The O-ring forces this seal onto the inside surface of the shock tube to seal the compression and rebound chambers. This seal rubs on the inside of the shock body and is a high-wear item.
A typical shock piston is shown. Of note are the three dots impressed into the piston just outside each of the three flow holes. This represents a dish shape of standard one degree plus three (three dots = three more degrees) degrees for a four degree angle of the preload dish. The height of the face of the piston at the center hole is lower than the height of the face out at the edges of the flow holes (three outer holes) and this forms a dish shape.
Under the piston seal lies the O-ring that presses it onto the inside of the shock tube. These two components work together to form a seal that separates the two chambers of the shock.