Shock maintenance is about problem prevention as much as it is about servicing. Yes, we need to service our shocks on a regular basis, but if the shock is asked to do more than it is capable of, or used in a way that is not consistent with its design, then the problems will come sooner.
So, we will give you suggestions for the prevention of shock problems and tips on maintaining and re-building your shocks. Unlike other components on your race car, shocks can perform multiple functions. Once we understand those functions and how we can help the shock do its job in a more efficient way, we will have less failures.
Differences in Shocks – The two main types of shocks in use today are the twin tube and gas pressure, or mono-tube, shocks. For both of these designs, the main things to worry about are the wear and failure of the seals, and the breakdown of the oil.
The maintenance for both types of shocks are very similar. If possible, gas shocks should be checked for pressure on a regular basis whereas the twin tube shock cannot be checked internally as easily.
Since a majority of racers in all divisions use mono-tube shocks, we will continue our discussion using those types in all of our examples. One of the primary reasons we do this other than the numbers of users is because twin tube shocks are not easily serviceable by the end user.
Maintenance Schedule – Shocks should be inspected visually on an event basis for obvious problems such as leaks, dents, binds, etc. Gas shocks should be monitored for pressure prior to race day. All shocks should be thoroughly checked after crashes, after running on extremely rough racetracks, or if the race car went airborne at any wheel.
After every race, the shock bearings should be cleaned, checked for binds, and then sprayed with penetrating fluid to keep them free from binding. Shock shafts should be spun to check for bends, and visually inspected for imperfections or “pits” that may cause seal damage or oil leaks.
Change the oil and freshening the shocks every 20 to 25 races in a normal season depending on the conditions and environment the shocks are exposed to. If you run on tracks where higher shaft speeds and temperatures are generated, you should probably change the oil and check the shock more frequently.
How To Check Your Shocks – The best way to check how your shocks are working is to have the shocks checked on a quality dyno by a competent technician. Users can make basic checks for bent shafts by completely extending a shock then compressing it while twisting the shaft back and forth all the time checking for tight spots.
If you don’t have access to a dyno, the best way to check your shocks is to stroke them by fully extending the shaft, put it on the floor, and give it a good push down. With the shock fully extended, there shouldn’t be any side play in the shaft. If there is, you probably have seal or bearing failure.
While you are stroking the shock, turn the shaft to check for bends. For shocks with high rebound settings, you’ll need to open up the bleed all the way to allow movement of the shock shaft.
The Causes Of Shock Failure – Anytime a shock is bottomed or topped out it can cause premature shock failure. One of the biggest issues with today’s dirt Modifieds or dirt Late Models is the extreme indexing of the birdcages.
If your shock is attached to this birdcage it could travel the end bearings past their full rotational range and bind the shock. The bind will cause a side load to the piston rod and will prematurely wear the O-ring and bushing in the closure nut and ultimately cause the shock to leak.
Even with shocks mounted to a clamp on the rear end, or front shocks mounted to the front hoop, there is a chance the housing will bind against the mount. This not only damages the shock, it can cause serious handling problems that are very hard to find.
The use of shock travel indicators helps us know how far the shock is moving and we can cycle the suspension through that range of motion at both the front and rear of the car. Then we can observe the shock mounts to see if there is any binding taking place.
Mounting The Shock – For each type of racing, there is a preferred mounting height for the shocks which dictates the piston position within the shock tube. This position is decided in relation to the amount and direction of travel each shock will experience.
For most applications, the rule of thumb used to be that 60% of the travel was allowed for the compression stroke. Ideally the piston should operate as deeply in the shock body as possible. This arrangement provides the most stability for the shaft and piston assembly and enhances seal, bushing and shaft life.
In any event, the shock cannot be allowed to bottom out or top out. This damages the parts inside the shock and can lead to shock failure. In today’s racing, there are many different setups that cause the shocks to move very differently than what we used to see ten years ago.
Dirt Late Models and Modifieds can extend the shocks fully at the left rear and pavement late models can compress the front shocks a considerable amount. The position of the shock at ride height should be set with full consideration of the way the shock will travel on the race track.
The shock mounts must be observed not only at ride height, but at full suspension travel to make sure there is no binding. The shock body can come in contact with the mount, or the mono-ball rod end could run out of rotational travel. Either way, the suspension will bind up and cause handling problems in addition to damaging the shock.
Re-Building The Shock – The actual re-build of the shock is a fairly simple and straightforward process. Again, we are talking about a mono-tube, gas pressure shock. If you are doing this yourself, first you need to obtain the parts that will be needing replacement. Those are the shaft seals, the piston seals, and new Schrader valves.
Bleed all of the pressure off of the shock body by removing the core from the schrader valve. This will be replaced anyway. Then with the shock in a shock vise with the shaft pointed up (you do have a shock vise, don’t you?), place the overflow ring on the shock body (you do have an overflow ring, right?) and remove the end cap.
Now you can remove the shock shaft and piston. Pour the oil in a container to be discarded appropriately. We will use new oil. Now we must remove the divider piston. Disassemble the pistons and the shock body and replace all of the O-rings, seals and piston bands. Again, check the rod guide for wear and replace if necessary. You’ll need a tool to get this out and we will replace the seal.
Before we reassemble the shock, think out how the shock performed last season. You have everything disassembled and out on the table so to speak. A valving change is a simple thing to do at this point. Hopefully you have a shock graph generated by a shock dyno so you can see the resistance at different shock shaft speeds.
If, during the season, you changed your setup to using new spring rates either softer (front springs) or stiffer (right rear spring or when using bumps) to better balance your setup, then you might need to make changes to your shocks so they can work better with the new spring rate.
The smartest thing most racers can do is send the shocks back to the manufacturer or a designated maintenance facility to do the re-build. Then they can run the shock on a dyno and send you a report that will show the exact rates. Then you can decide on any changes that might be necessary with the advice of the professional.
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