Professor Morris in the laboratory. Photo: Joe Bonnello
Author: Professor Tommy Morris
Welcome back to the 18th class in Dirt Sports University’s Shock and Suspension Series. In trying to plan out the last few classes in our curriculum on shocks and suspension, it has been a challenge to be sure that we have done a complete rundown on all the knowledge and information that you will need to know. We have condensed several decades of design, testing and racing in off-road in an effort to save you from the same time, pain and money it took to learn this knowledge. If you add up the development costs spent by several teams through these years, millions of dollars has been lit fire to in the quest of finding speed through suspension development. We have worked hard to give you a well-rounded education on a wide variety of vehicle design, parts selection, components and the issues you need to consider and implement to optimize your off-road vehicle suspension system. In this class we want to review your shock absorber maintenance habits as well as your time and energy invested in testing and properly tuning the total suspension package. You cannot expect your vehicle to perform at its best if proper preventive maintenance has not been performed in a timely manner on the shocks and suspension parts. I don’t mean this just to go race, but for testing also. How can you expect to test and tune your shocks properly if they are not in top condition themselves?
Fresh shock oil (on the right) and used shock oil after 200 miles of testing.
SHOCK OIL: This subject could be a class all in itself. Take a look at the comparison of the two clear cups of red shock oil in the picture. The shock oil that is red in color is just about the best shock oil that you can find. One cup is new oil while the other has 200 miles of hard testing on it. You can clearly see through the new oil, while the used oil is cloudy with contaminants. There is nothing you can really do about this happening. When your shocks are punished from running through all sorts of terrain, there is wear to the piston band, rod guide, cylinder wall and all the other internal components surfaces working together. These wear particles are extremely tiny but continue to act as an abrasive as they flow throughout all the working pieces in your shocks. The longer and harder you run the vehicle, the dirtier the shock oil gets. Without proper shock maintenance you will limit the overall life of all the internal shock parts. There are a variety of oils available, but we will stick to a simple overview. Most of the shock companies use standard hydraulic oil that is clearish gold in color. This oil is relatively inexpensive and allows them to keep the overall price of the shocks a little lower, and through most of off-road history this standard shock oil has worked fine. Now times are different and the desert and mountain trails are not as smooth as they once were, as off-road has grown from its infancy. This has led to the need to find an extreme-duty shock oil with better lubrication qualities and a much higher temperature rating. Fox Shox has helped lead the way in this department and uses Extreme shock oil derived from aerospace applications that can handle 450 degrees in all of their race shocks. This oil is what was approved for the Ford Raptor outfitted with Fox shocks to handle the prolonged service life needed in the abusive off-road environment and is now the choice of many of top racers in off-road. The regular shock oil temperature rating is good to around 300 degrees and after continued use above this temperature the oil goes south. It becomes very obvious when opening up an overused shock as it smells like rotten eggs with the oil being very dark in color. This breakdown of the oil’s lubrication properties now allows additional wear to the internals. If a vehicle is not abused too much and the shock temperatures are kept under 260 degrees, this standard shock oil will work fine. If you push the limits on a regular basis, you would do well to use the Extreme red shock oil when servicing your shocks. It’s like going to the auto parts store and buying plain old low-cost engine oil or stepping up and buying the higher-grade synthetic oil. It costs two to three times more, but dollar for dollar this is a good investment for your shocks just like it would be for your engine or transmission.
Maintaining shocks and replacing wear items is vital for performance.
SHOCK MAINTANENCE: Many of you think that the time to look inside the shocks and service them is when they are leaking oil on the floor of the garage. This is not the proper way, especially when you consider how much work the shocks do during off-road use. You are not dealing with a simple street car where after 40,000 miles you throw on another set of shocks. One time to the desert and you are changing the engine oil, repacking the CV joints, cleaning the air filter and so on. Some worry about the engine oil going over 260 degrees yet think nothing of the shocks running at high temperatures. What happened to taking care of the shocks that you abused so well? Inside of the shocks there is a relatively small amount of shock oil when compared to all the hard use they are put through. There is no oil filter to help keep the shock oil clean and free of dirt and worn metal particles. Sure, there is a shock shaft wiper to keep the dirt out and oil seals to keep the shock oil inside where it belongs, but small amounts of dirt still get past them all and into the shock oil. Now think about all the sand and rocks pelting against the shock shaft creating little pits in its surface that are carrying tiny particles of dirt into the shock while at the same time cutting away at the fragile oil seals. Inside of the shock reservoir is a dividing piston that separates the shock oil that flows in and out of the reservoir from the high nitrogen gas pressure charge. This dividing piston can move several inches during the shock’s use and allows the shock to do its job properly with just a simple O-ring to get this job done. Shocks can easily be described as a lot of simple parts getting a big job done. I hope that we have painted a clear picture of what sort of maintenance is expected of you to do here.
The right tools for the job are also critical for maintenance.
LEARN SHOCK MAINTENANCE YOURSELF: If logistics and cost are an issue for your shock servicing needs to be done when necessary, then consider learning this craft for yourself. It is not as difficult as you might think. This knowledge can also be helpful if you have aspirations of going testing and learning what valving shim changes do for you. One of your main concerns will be attention to detail when you are getting into the valving shim stacks to ensure the proper location of each shim in compression and rebound along with the piston orientation to them. This should be written down for reference during reassembly after cleaning and inspection. Following this detail will be the assembly process to get the reservoir-dividing piston set in the correct position and then to get all of the air out of the shock while filling it with shock oil. The rest is easy. The amount of specialized tools for the job is minimal if you have a decent set of tools now. Some of the tools you can even make yourself. A call to your shock brand company should be able to help you with a list of the special tools you will need. Several shock brands have good instructions for servicing shocks available on their website. You will need to plan enough time to get the seals, O-rings, oil and any other parts that might need replacement. Once you get a handle on the usual service parts that are needed regularly, you can keep them on hand to make the servicing process quicker and easier.
SHOCK PERFORMANCE vs ENGINE POWER: When was the last time that you placed your shock needs right alongside of your engine needs? An engine dyno sheet is usually the most important piece of paper that most care about. Ask for a shock valving sheet for your shim stacks or a spring adjustment spec sheet and you usually get a deer in the headlights look. Most of you will sell your mother or child if an engine builder tells you that he can get 22.6 horsepower more out of your engine. The sad part is most will jump at that and shell out hundreds, if not thousands, of dollars more to have a bit more power, but the shocks and springs have as much to do with making your vehicle go fast and be reliable as the engine and transmission setup. Please excuse me for getting wound up about this and possibly sounding disrespectful. Take a look in your checkbook, receipts and credit card statements. Then add up how much you spent on engine-related expenses in comparison to shocks and springs. Get the picture? If this even remotely sounds like you, there is help that can come your way if you reach out for it.
A shock spec sheet (right) is just as an important as a dyno sheet.
TIME AND MONEY WELL SPENT: Lots of money gets spent a number of ways when you feel you can justify it to yourself, but when was the last time that you planned a proper, organized suspension test? I don’t mean a function test right before a race, but an honest real test to focus on making your vehicle suspension more comfortable, reliable, better handling, run cooler temps and go faster. Don’t kid yourself on whether you are setting yourself up for being a real competitor with the opportunity to place at the top of your class or if you will just be one of the participants involved in the event. There is a big difference between the two, and you need to understand where you are positioning yourself to fit into.
THE PROCESS TO TEST: Now is the time to step up and get out a calendar to plan a proper test. Depending on how your vehicle really works and not what you have dreamed, this process can take a couple of days of testing or sometimes several tests with time in between needed to go back in the shop and fix some fundamental flaws. You don’t have to have a giant budget or be a rocket scientist yourself to make this happen either. If you are really budget-conscious, you can usually work with the manufacturer of the brand of shocks you have when they are going to have a test session that you can be part of. This means there will usually be several vehicles at the test where you can get some guidance, but be prepared to have all the tools to do all of the R&R of your shocks and, in many cases, take the shocks apart yourself. Depending on where you live in relation to most of the name brand shock companies that are in Southern California, this can be geographically challenging for you. There are private tests that can usually be arranged with the shock companies and, depending on the calendar dates available and location of the test, the cost involved can get up there.
HIRED GUNS: This is sort of like hiring a soldier of fortune or a mercenary to help your cause. There are a few suspension tuners out there who specialize in getting your program sorted out. The services provided can cover the entire range of your vehicle needs, from engineering reviews of every system in your vehicle all the way to full support of a test and tuning session. Most of you feel you have all of this covered, but odds are that if you really look at the results of your program you might find you are lacking. Seek the proper support or person to analyze your situation and set a better direction to get the job done. Check with leaders in the off-road industry to find out how to contact these elusive characters.
IN CLOSING: Think through what has been discussed in this class and how an improved maintenance and testing program for your shocks and suspension can help your vehicle in ways that you had not fully understood previously. Reach out and seek the help that will best fit your needs and expected results.
HOMEWORK: Time is wasting. Get the tools gathered up along with the technical information that you need and dig into one of your shocks, or find friends’ shocks to test this out on. This will help you in our next class where we will discuss more maintenance and tuning tips. Remember that knowledge transforms itself into speed that you need.
Class Dismissed. Professor Tom Morris Dirt Sports University and School of Hard Knocks