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Shock and Suspension 119

Posted in How To on June 1, 2013
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Professor Morris in the laboratory. Photo: Joe Bonnello

Tommy Morris Photo 68808963 Professor Morris in the laboratory. Photo: Joe Bonnello

Author: Professor Tommy Morris

This Month’s Lesson: Closing Notes For Your Shocks and Suspension Class.

Welcome back to the 19th class in Dirt Sports University Series on Shock and Suspension. In the making of the University Series here in Dirt Sports magazine we discussed having a classroom format to help pass along knowledge to the readers that would help them as their interests grew in off-road and the vehicles that they either wanted to have, currently owned or dreamed of for the future. This discussion all came about a couple of years ago during an overnight vehicle test in Lucerne Valley, California, when we were doing some suspension tuning on the Dirt Sports Project Plug N’ Play Alumicraft prerunner buggy with the nice folks from Fox Shox and Eibach Springs. As the test day turned into night with camp fires burning and good old stories being told, there was plenty of mineral spirits being consumed thanks to the owners of Azunia Tequila who came out for the daytime testing and evening abuse. It was during this so called “office meeting” that the obvious first class for the newly created Dirt Sports University Series would be on shocks and suspension. We even called it 101, like that was all it would take, and at the time we figured this would only take a few classes and then we would be onto the next subject. As time has passed, you have been able to bear witness to all of the information, details, parts and pieces that are involved in today’s suspension and shock packages and the efforts involved to tune them properly. Even after 18 classes on the subject, there is still more that can be dug into, but in the reality of time and space we need to get to another subject in our class sooner than later. Like any class or subject that you are interested in, the responsibility is on you to continue your education beyond what you have already learned here. Our duty is to pick a subject that sparks your interest, and then help you to gather further information that will guide you onto hands-on experimentation and experience. Talk is cheap and you need to back it up with actually working on the subject matters that we are schooling you in. In this class we are going to finish up on some maintenance items, along with some closing suggestions and thoughts.

AS SEEN AT THE RACES: We have covered many items on the proper care and maintenance of your suspension system. If you go back in our classes you will remember the discussion on coil springs and how they are one of the most highly stressed parts of your vehicle’s suspension system. While I was wandering through and looking at the vehicles in line for contingency and tech at the Best In The Desert Mint 400, a two-seat unlimited buggy caught my attention. Here we had a nice looking off-road racecar with good paint, shiny wheels and new tires. So what have I got to complain about? The rear coil springs looked like someone had used them for target practice with a shotgun. The rocks that come off of the front tires can do some real damage to the outer surface of the coil springs and that can lead to the spring breaking in pieces. I wondered what sort of shock maintenance had been done if the coil springs looked that bad. I know of at least one racecar that broke a coil spring at the Mint 400 from just plain using it for too long, and I would expect that there were a couple of others as well. New race tires are $300 to $500 each. New coil springs for the rear of a buggy are $86 to $195 each retail, depending on the diameter and length. Your budget dollars spent in the proper areas will serve you well for reliability. The front springs usually do not see this same pitting damage, but the rear springs need to be looked at as a normal replacement item when they show excessive pitting. There are outer wraps that velcro in place around your springs that can help to prevent spring and shock shaft damage. The only downside to these is that your shocks will run a little warmer during hard use due to the blocked airflow to the shock shaft and part of the shock can. Other than that they are a great item to use.

PROPER PREPARATION: As we discussed in the last class, the off-road vehicle is an entire system and putting new tires on a vehicle along with paint and stickers is not always the key to success. When you go to the races take a look over and under the usual front runners’ vehicles that place well in the top of their respective class and you will see the care and preparation taken to ensure that they are successful. If you plan on succeeding in off-road racing, or any other racing venue, you need to mirror what the winners are doing in proper preparation of their vehicles. Proper planning and preparation for success is a must. Otherwise you are merely able to be a participant.

Knowing your piston position at ride height is critical. KNOW YOUR BYPASS PISTON POSITION: It seems that occasionally when testing there is a question of which bypass tube is affecting the ride height zone. If the bypass shock length has been figured correctly for the proper suspension travel, along with the proper motion ratio for the intended use and the bypass tubes fitted in the proper positions, then this question does not come up much. With that said, there are many vehicles I have seen where the shock piston at ride height is very close to or past the ride height bypass tube(s). This can happen from mismatched shock lengths for a vehicle’s needs, incorrect parts and pieces, or the ride height versus shock travel and length is not what it should be. It can create challenges during tuning if you are adjusting the wrong compression or rebound bypass tube for the zone. All is not lost, you just need to figure out what the quirks are with your particular setup and adapt to it as best as you can. The shock piston position at full suspension travel can also cause grief if you are not stroking the bypass shock through all of its travel. It is possible not to get all the way into the bypass bump zone. This is the last bit of shock travel for which there is no bypass tube adjustment, usually the last few inches of fully compressed shock travel. If your skid plate is smacking the ground and you are not using the full bypass shock travel, then you need to stand back and evaluate your issue of mismatched suspension travel versus shock travel. Work it out and fix the problem. As a rough rule of thumb you can figure that with your bypass shock fully extended when the shaft end is disconnected from the vehicle’s suspension, the valving piston will be just above where the compression bypass tube check valve assemblies are welded to the shock can. If you are in doubt about where this is and what the correct position and measurement are, be willing and able to take your shocks apart to find out. Then you can measure the shock shaft assembly against where the valving piston actually is. Measure this and make a sketch of all the dimensions that are normally hidden inside the shock and keep this for future reference. You should have already put together a shock-tuning book with all the pertinent information for the shock, valving, springs, etc., in your suspension system.

Fox Shox Photo 68809008 Knowing your piston position at ride height is critical.

Measuring the piston and shaft assembly.

Piston And Shaft Assembly Photo 68808966 Measuring the piston and shaft assembly.

Checking the floating piston depth. BENT SHOCK SHAFTS: This subject came up when an individual bent a shock shaft and then replaced it himself with a new one. The problem was that a thorough inspection of all the parts that the shock shaft works in harmony with was not done. It ended up that the top wiper cap as well as the seal gland and bushing assembly also suffered damage from the bent shaft traveling through them. Also along the way the shock-valving piston was damaged from running a little sideways up and down inside the bypass shock can. Fortunately the shock can did not suffer damage from this. Always do a complete inspection of all of the shock components when any sort of damage is being repaired.

Floating Pistion Depth Photo 68809011 Checking the floating piston depth.

CHECKING THE RESERVOIR: Tire pressure is something that most of us think about and check on a regular basis. There is the good old-fashioned way of looking at the tire and realizing that a large bulge in the tire sidewall has set off an alarm in your head to get out the tire pressure gauge and look around for the air hose. Then again, some like to kick the tire in some form of air pressure measurement system. I haven’t quite figured out yet how to calibrate that one. I would trust a high quality tire pressure gauge myself. Your shock absorber nitrogen gas pressure is another of the common maintenance items that is frequently missed or neglected. We have shown you the proper nitrogen gas pressure checking gauges in past classes. Along with checking shock reservoir nitrogen gas pressure, one should also check where the internal floating piston position is in relation to the reservoir canister connection end to the shock. The floating piston that separates the high nitrogen gas pressure from the shock oil is very highly stressed and uses a simple O-ring to do its job. Be sure that the outer reservoir can does not have any dents in it from rocks or other accidents. Any dents in the canister can cause damage to the internal O-ring and piston as it moves across the dent. This will allow the oil and nitrogen gas to mix together, creating a foamy mixture of shock oil that does not provide good dampening characteristics. Just checking the gas pressure will not let you know all is well inside the shock. A common problem is to have the nitrogen gas pass the O-ring and mix with the oil. This can happen for the entire reservoir area or just a portion of it. A telltale sign is when letting the gas pressure out that a heavy oil mist sprays out (a slight oil mist is okay). Another sign is once you remove the valve core, hold the shock and reservoir so that the valve core end is facing down and see if oil drips out. A drip or two can be normal, but any more than that needs investigating.

WHAT HAPPENED: If you are out testing and doing a re-valve, you can experience evidence of the nitrogen mixing with the shock oil when taking the shock shaft and gland assembly out of the warm shock oil and seeing a nice foamy layer as you look into the shock. There have also been times where a shock had passed all of the gas and the floating piston all the way up against the reservoir end cap at the Schrader valve end. This means that replacing the internal O-ring along with checking for scoring of the inner reservoir wall is needed before much of anything else. A full shock tear-down is usually needed at this point, and be careful as the full gas pressure is now trapped inside the shock and you will need to figure out how to release it safely. This issue involves another series of steps to resolve, so proceed carefully. Follow me through the next step if you have not done it before. It is simple and effective, as well as a very important step in being sure that your shocks are in good health.

THE DIPSTICK TOOL: A very simple means of checking the floating piston position is to release the nitrogen gas pressure and then remove the valve core. You can make a depth-checking dipstick from a piece of 3/32-inch welding rod or anything similar. Insert the dipstick into the valve core housing hole until it touches the floating piston. Try to have the dipstick near the centerline of the reservoir and wiggle it around a bit while lightly sliding it in and out to be sure that you have reached the true backside of the piston and are not hung up on a design feature. Put your finger at the end of the valve housing on the dipstick and slide the dipstick out. Now overlay the dipstick with your finger in place on top of the reservoir and this will let you know where the floating piston is sitting. Depending on the overall length of the canister, the floating piston depth can vary as to the proper amount of oil level that is desired. A normal depth has the floating piston within an inch or two of shock oil in the reservoir. If you find that the floating piston is all the way bottomed out, this can account for a clacking noise you may hear when the suspension goes to full droop. This noise is from the reservoir floating piston slapping into the reservoir can end cap. This is not very common, but it does happen at times. Follow the instructions from your shock brand manufacturer for removing the shock shaft and seal head assembly and add the oil needed so that the reservoir piston is in the correct position after the shock is re-assembled. This is assuming that your shock was in good condition to start with and was not leaking oil somewhere.

VEHICLE WEIGHTS: Before you go out too much with your off-road vehicle to play, or to put your serious face on and go racing, it is important to have done your proper homework first as to what your vehicle is really going to weigh for the application in which you are going to use it. This means that you should plan to do some testing with all the weight that the vehicle could possibly get piled into or onto it. All too often a significant amount of weight is forgotten about during the shock and suspension tuning process. The actual weights of the occupants along with any tools, parts, fuel, etc must all be accounted for or you can be way off of the mark in final vehicle use. For example, this shows up later when you load up your four-seat buggy with a full tank of fuel along with a roof rack loaded with gear and the all-important ice chest. If you have four adults in the buggy, the total weight can climb really fast. All of a sudden the great handling car you had with a scant two people zipping around in it turns into a big top-heavy hog.

SPRINGS FOR TESTING: Do not be afraid to try a combination of higher-rate springs, especially on a vehicle where the weight can vary significantly depending on what you are packing to go with you. Using a higher spring rate will help to stabilize the vehicle ride height under different weight loads as well as help control body roll and front to rear vehicle balance.

IN CLOSING: Through these classes we might not have told you what you want to hear, but we have always been truthful and realistic with you and expect you to be the same with yourself as well as those who are helping you. People, along with their various emotions and skill levels, can be interesting to work with. Chose your words carefully and know that all of us want to be part of a winning team. There is a skill level for all to help and participate with on a vehicle and team when looking to achieve success.

HOMEWORK: If you have missed some of these classes, make the effort to get a hold of what you missed. Remember that knowledge transforms itself into speed that you need.

Class Dismissed. Professor Tom Morris Dirt Sports University and School of Hard Knocks

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