Click for Larger Image	Basics The shock. Its purpose is to dampen the up and down movements of the rear wheel. It also comes in handy for holding the rear spring. The differences in the shock for a single shock rear suspension and a dual shock set up are very similar. Their mounting and/or linkage systems are basically the only difference. Dual shock set ups are pretty self explanatory so I won't go into them too much. The shock itself is similar or the same as a single shock set up. Some of the older shocks had some unique damping systems. One that comes to mind is one that had the rebound damping controlled by six orifices shut by spring loaded steel balls. During rebound, the movement of the shaft/piston would force the oil against the steel balls and raise them off their seats. I'm not going to cover much of anything except what is in most all shocks for the last decade. This would be a series of spring steel shims controlling oil flow through a series of holes in the shock piston. Since a visual will help immensely, I'll stick a few shots in and describe them. These I took while installing a Gold Valve in the shock of a '99 YZ 125. I'll show the differences between the stock piston and the Gold Valve. One word to cover my ass. This is NOT an advertisement for Race Tech products. I am a Race Tech distributor and this was a shock I had apart for one of my customers. It just so happens 70% of the shock work I do is Gold Valve installation, so that's what I had it handy to take pictures of. Some other suspension shops revalve by simply changing the diameter, thickness, and/or quantity of the shims. Some will drill the stock piston to enlarge the holes the oil passes through. There are other companies who have different pistons beside Race Tech also. The theory is the more oil that can flow through the piston, the more damping relies on shim selection. This means we can control it more thoroughly.
Gold Valve and the Stock Shock Piston	This is a picture of a Gold Valve and the stock shock piston. Notice the 3 large oblong holes in the Gold Valve. The shims are held tight against the face of the valve and oil is forced through the holes bending the shims off the face. This is where the damping occurs. This shows the compression side of the piston. The rebound side has much smaller holes on both the stock and aftermarket pistons.
Shims - Ready to Install	Here is a shot of the shims in their respective position ready to install on the shock shaft. The shims on the left are the compression shim stack and the shims on the right are the rebound shim stack. Okay, we know the shims bend off the face of the valve. The amount they bend controls the damping. This is controlled by a few variables, one of which is known as the clamping shim. This is the smallest shim at the ends of the shim stacks. This is what tightens everything together. This means only the edges of the shims bend. The outer diameter of the clamping shim determines how much of the other shims cannot bend. If more of each of the shims are allowed to bend, the valving feels softer. If we stack more of the same diameter shims together, this makes it harder to bend and makes it stiffer. Same thing if we use thicker shims. This will make it harder to bend and make it stiffer. Depending on which shims we use, we can alter the damping characteristics virtually any way we want.
Stock Piston with Shims	Here is the stock piston with its shims displayed. From upper left is the plate that the assembly tightens against, the compression stack beginning with its clamping shim, increasing in size , the piston itself and then the rebound stack ending with the end plate that the nut tightens against.
Gold Valve Installed on the Shock Shaft	Here is the Gold Valve installed on the shock shaft. The reservoir holds the bladder (or floating piston in some shocks- Ohlins, for instance). This allows us to pressurize one side of the bladder/piston to help keep the shock oil from cavitating (foaming). You can see how well it works when you pull the shock apart and the oil foams up like a Coke after being dropped. Altering the nitrogen pressure can affect compression damping also. Normal pressures run from 140 psi up to 300+ psi. I usually use 175psi, except for XR shocks that use 225 psi, when doing a revalve. Remote reservoirs function the same as an attached reservoir except they obviously have a hose between them to allow a different mounting position.
Rebound Adjuster	The rebound adjuster is nothing more than a needle that is screwed into a fixed seat that controls a bleed passage around the piston. The adjuster is a tapered screw that pushes the needle further into the shaft the farther the screw is screwed into the clevis. It is a little difficult to see, but here is a picture of the adjuster screw. This is looking down into the clevis with the shaft removed.
Shock Shaft with Rebound Needle.	You can see the visible part of the adjuster on the right side of the clevis. The adjuster is the brass screw in the very center of the hole.
	The compression adjuster works a little differently. As the shock moves through its travel, oil is displaced by the volume of the shaft assembly and is forced into the reservoir. The compression adjuster controls the rate at which the oil goes into the reservoir. This is also a needle and seat adjuster. Some shocks have ball type joints (a spherical joint) at the ends, some have needle bearings. Some of the spherical joints have a bushing surrounding the ball that do not require grease. Check your shop manual to see if they recommend lubrication. Needle bearings obviously need a good quality waterproof lube. I use the Bel-Ray grease. It's nice and thick. Good stuff.. Maintenance We'll assume you can get the shock off the bike without any help. If you can't, you probably shouldn't be trying to attempt any repairs to the shock itself.
Shock with Spring	Measure the spring installed length and the adjuster settings and write them down. Loosen the spring preload adjuster until the spring is loose. There are a couple different methods for holding the lower spring seat to the shock. One is a circlip that is virtually hidden until the outer collar is pushed towards the spring a little. It is common to have to tap it lightly to get it to move. This should expose the circlip. Remove the circlip and the spring seat will slide over the lower end of the shock. This KYB shock has a split collar that can be slid out sideways once the preload adjuster is loosened far enough.
Shock without Spring	Okay, we have a shock without a spring on it. Remove the schraeder valve cap and release the gas pressure. On most shocks, the valve points straight down out of the reservoir. Using a socket to protect the valve stem, tap the reservoir cap down far enough to expose the circlip. Use two small flat blade screwdrivers to remove the circlip. It ca be a little difficult to explain, but push the circlip down until it is out of its groove and use the other screwdriver to pull the circlip over the tip of the first screwdriver. In the next picture, this circlip is the one in the shock body itself, but the circlip and removal are the same. I've got the circlip pushed down and I am ready to pull it up with another screwdriver. If you scratch the surface much more than 1 or 2 mm below the circlip groove, you can create a leak due to the seal not sealing correctly. Be careful.
	Pull the reservoir bladder out of the reservoir body. Normally I use a valve core removal tool screwed over the end of the valve stem and pull up with that so nothing gets damaged. The bladder may be a little stubborn. Wiggle it back and forth to remove it. Now to remove the guts of the shock. There is a cap on the end of the shock body that protects the seal head. This metal cap is pressed into the end of the body. Use a sharp chisel or punch and tap it up. Tap evenly from opposite sides to prevent it from getting wedged too tightly. We don't need to break any expensive parts. I use a clothes pin to hold the cap up out of the way. Now the seal head is exposed. Showa shocks have two circlips and another collar between the circlips. First thing you'll need to do is remove the one circlip that is visible. A pair of snap ring pliers can push the clip out of place enough to get your screwdriver tip under it and pull it off. Push the seal head down. On Showa shocks this will leave a washer resting on the lower circlip. Now you can remove this washer. Otherwise it can be a royal bitch trying to get it out with the seal head in position. With the washer removed, you'll be able to see the lower circlip. KYB owners won't have to deal with this first circlip and washer business. Just push the seal head down until the circlip is exposed (just like the above picture shows). Remove the circlip. Now you can pull the shaft assembly out. Normally wiggling it will be enough to remove it. Sometimes I've had to tap on the clevis end to get the shaft out. Be SURE you don't have it cocked off to one side. Remember, you're dealing with some really expensive stuff. Screw something up and you'll go from saving $50 to spending literally hundreds.
Shaft Assembly	Here is the shaft assembly once we get it out if the shock body. From left to right, the clevis end, the bottoming bumper, the cap, the seal head and the piston and shim assembly. If we were doing an oil change we could rinse everything off with brake cleaner and reassemble it. We'll get to that in just a minute. We'll finish pulling this one all the way apart in case you're replacing the seal or bushing or the bottoming bumper.
Loosening Locknut -  Replacing Bottoming Bumper without Oil Loss or Full Disassembly	Actually the bottoming bumper can be replaced without losing any oil (shock still fully assembled without the spring) by removing the clevis end. This is relatively easy and painless. Once the nitrogen pressure is released out of the reservoir, the clevis end can be taken off the shaft and the bumper replaced. There is a locknut (normally a 22mm) that is right at the clevis end of the shaft. You can use this to unscrew the shaft from the clevis end. The next picture shows the locknut being loosened but without the rest of the shock. As long as the rebound needle isn't removed, you won't lose any oil (provided all the pressure in the reservoir is released). A little red Loc-Tite on the shaft threads and reassembling and you'll be ready to go. It would be a good idea to mark the locknut position in relation to the clevis end so you have a way of knowing when it is fully tightened .
	Okay, back to removing the piston and seal head. The nut that holds the piston on the end of the shaft is peened in place from the factory. This peening needs to be ground/machined off so the nut can be removed without damaging the end of the shaft. Some shocks have a check
Here is what the peening looks like.	valve assembly in the center of the shaft. On these shocks, the peening also holds the check valve in place. It is critical that this peening is removed very carefully. If you're unsure of whether your shock has this check valve, grind the peening as though it does have one. We would rather be safe than sorry. Here is what the peening looks like before it is ground away.
Loosen the Nut	What you want to accomplish is to remove enough of the peened area to facilitate the nut removal but leaving the center intact. This is what it looks like after I've removed enough take the nut off.
Here's what it looks like when done correctly.	Now you can loosen the nut. If it begins to come off too hard, remove a little more along the sides of the peening. Once the nut is removed, you can use a file to remove any burrs and a thread file to restore the threads. If you try to use a tap, it can cut new threads if it doesn't start in the same place. Be careful. Here's what it looks like when done correctly.
After Removal	Now you can pull the piston off the end of the shaft. A coat hanger cut and bent in a "U" shape can be useful in holding the shim and piston assembly together. Here is what we have when the piston assembly is removed. Now the seal head can be removed.
Seal Head	This is what the seal head looks like once removed. The seal and bushing can be changed but it isn't much cheaper than replacing the seal head assembly. You can save maybe $20-25 by changing the individual parts.
Bleed Hole	The shock bumper can now be replaced if it is needed. While we have the seal head off, it can help the bleeding if we drill a hole in the side of the seal head. Showa shocks come with a hole from the factory. A 1/8" hole halfway between the sealing o-ring and the bottom edge will work wonders. In the next picture you can see the hole. Drill just deep enough to get through the wall of the seal head. A shot of brake cleaner will rinse out any metal shavings.
	Now reinstall the seal head. Make sure you don't fold the dust seal under when installing it over the step of the shaft. If you're installing an aftermarket piston, this is where it comes in. Be sure to have the larger shims (compression stack) facing towards the clevis end. If you are changing anything in the piston assembly (shims, piston, etc) you need to make sure the piston is spaced up so the step (directly below the threads at the end of the shaft) is not exposed. What happens is the nut will tighten down against this step instead of tightening down against the shims and piston.
Without Spacer Installed	This is what it would look like if NOT spaced properly. The Gold Valve shim stack and piston is thinner than the original and needs to be spaced out. You can see the brass spacer installed in the above picture. The picture at left shows the step before the spacer and nut are installed. If a nut was installed without the spacer, it wouldn't tighten down properly.
	Be sure to use a new nut with red Loc-Tite. Torque is normally 24 lb/ft. I torque it to 30 lb/ft because if this nut comes loose, the results can be disastrous not only to the shock but to the rider also. Normally the KYB thread is a 10x1.5 and the Showa is a 10x1.25. Don't guess, you need to be certain of this. There is a fiber bushing that goes around the piston. If this is not in good condition (edge rolled or torn), now is the time to replace it. The aftermarket bushings are split and need to be held in position while the piston is inserted into the shock body. We're not quite ready for this though. Okay, we have the shaft assembly ready. We have the body thoroughly rinsed out with brake cleaner. The reservoir bladder is rinsed clean and is installed on the reservoir cap. Remember what Grandma said. "Cleanliness is next to Godliness". She must've been talking about shock servicing. We're ready to reassemble the shock. The method I use is different than some manufacturers use. I've found bleeding is much easier with this method and getting the proper amount of oil in the shock is more of a sure thing. Here we go.
Inserting the Bladder	Tighten the shock body in a vise with the openings pointing straight up. Place a drain pan directly under the vise on the floor. This will get messy. Pour new oil in the reservoir until it is almost half full. Insert the bladder into the reservoir.
It will be messy!	If the reservoir end cap has to be pointing a certain direction (like this YZ 125), now is the time to point it in that direction. Push the bladder into the reservoir until oil gushes out all over. Like this?..
Pressurize Bladder Add Oil	Push the bladder into the reservoir until the circlip groove is visible. Install the circlip and pull the end cap up into position seated against the circlip. Now you need to pressurize the bladder with 35-40 psi of air. This will force any air trapped in the compression adjuster out, into the shock body. Add oil into the body until it is about an inch from the top edge. This is what you should have?.
	Now put the business end of the shaft assembly in the body. If you have a new piston bushing, you'll have to hold it in place while you push it into the body. Push the guts into the body slowly. You should see a lot of bubbles coming up through the oil. Don't push too hard because oil will come shooting out the hole in the side of the shaft. I told you this would be messy. Now run the shaft through its stroke a few times. Don't pull the shaft up so far it sucks air through the hole in the side of the shaft. This will result in pulling more air in under the piston. Watch closely. If it sucks air, you need to start all over with the bleeding.
Fill Body - Bleed Air Bubbles	Once you get it so no more air bubbles are coming out, pull the shaft up as far as you can before sucking air. Take a rubber or plastic hammer and tap the clevis end of the shaft assembly. You want to tap it hard but don't pound it. What this does is makes the oil force the compression shims off their seat far enough to release any trapped air bubbles. Do this until no bubbles come up. This step is important. Don't take it lightly. Give the oil a few minutes for the very small bubbles to surface. Fill the body with oil to near the top edge. It should look like this?
	Once you have the air bled out from under the piston, we're ready to push the seal head in. Tilt the shock body to one side just a little. Now pull the shaft assembly up as far as you can with the body full of oil. You want to get as much oil in the body as you can. Turn the seal head so the bleed hole is at the higher side of the tilted shock body. You want any air trapped under the seal head to go to the high spot (where the bleed hole is). Push the seal head in place. You should see bubbles coming through the bleed hole. The seal head will stop moving down. While holding pressure on it, release the pressure in the reservoir. The seal head will go further into the shock body. Keep pushing down and continue to release the pressure in the reservoir until the seal head is down far enough to expose the circlip groove. Install the circlip. Now pressurize the reservoir with air pressure. Normal shop air will work fine (at least 90 psi or so). Here's where we test the shock to see if it has enough oil in it. With the damping adjusters set at full soft (counterclockwise) and air pressure in the reservoir, push the shaft into the shock. It should go in smoothly and return fully by itself. If it doesn't return 100%, then you may not have enough oil in it. Once you're satisfied the internals are in good order, rinse the outside with brake cleaner and tap the cap into the to of the shock body. Rinsing the shock off can be important in case you suspect a leak after it is reassembled. A clean and dry shock will reveal any leaks quickly. Put a little grease on the preload adjuster threads, reinstall the spring, set it to its correct length, reset the damping adjusters and you're ready to put the shock back on the bike. Adjustments Adjusting the clickers can be a science in itself. There are a lot of variables between individual bikes, so I'll only cover basic settings. New bikes should be set as close as possible initially. It doesn't cost a thing to set it up and can make the new bike experience much better since some new bikes come pretty far from the best settings. Some forks take a while to break in and adjusting the compression clicker to a much softer setting initially can make life easier while waiting for things to loosen up. Race sag is the difference in the measurement between the bike on the stand and the bike with a fully dressed rider aboard. Measure from the rear axle to a reference point near the rear fender/seat. A lower edge of the rear fender works well. The important thing is to measure from the same two points. For the measurement with the rider aboard, the rider should be standing up. One variable is where the rider sits during the measurements. If he changes his seating position even a little between measurements, it can have a significant effect on the settings you end up with. Standing up eliminates this variable. This means a 3rd person is needed to balance the rider/bike. Suck up to the wife/girl friend and she may give you a hand if she isn't still bent about you getting the new bike. Drag in the suspension pivots can affect your measurements. On the first measurement, push the rear fender down slowly and let it rebound slowly. Check your ruler. Now pull up and let it relax slowly. Check the ruler again. The difference in these two indicate how much drag there is in the pivot points. If there is more than 10mm, something is binding enough to need attention. For accuracy, this pulling, measuring, pushing, measuring should be done at each measurement. But since there is a relatively large range of adjustment anyway, this may not make much difference. Just be aware of it. Sag should generally be set at about 1/3 wheel travel. This means about 100mm for most full size dirt bikes. Some bikes have an adjustment range of around 90mm to 105mm. The less the spring is compressed does not necessarily mean the softer the ride will be. Due to the progressive ratio designed into the linkage, setting the spring stiffer can make the ride softer?.. Say what?!? The linkage is designed to move the shock less as the suspension moves through its travel. This makes it soft at the beginning of the movement and stiffer as it goes through towards the end. This makes it more resistant to bottoming but still allows it to be plush over smaller bumps at full extension. So if we set the spring stiffer, it will move the ride height into the softer ratio part of the travel. This is one reason a "too soft" spring rate can give a dead feel to the rear of a bike (compared to how it should feel). Once you get the sag set, you can check to see how close the spring rate is for your weight. Check the sag again without a rider aboard. This is known as static sag. You should get between 15mm and 25mm if your spring rate is correct for your weight. If the static sag is less than 15mm, your spring is too soft for your weight. If the static sag is more than 25mm, your spring is too stiff for your weight. I know this may sound backwards, but this is due to the preload applied to the spring to get the rage sag correct for your weight. Compression adjustment can give a variety of adverse symptoms. It can be a good idea to have someone watch what is really happening to verify your feelings. Is it "really" bottoming over that jump? Is it harshness due to improper valving? The clicker is a low speed adjuster. This means it affects the damping concerning relatively slow hits (jump landings, G-outs, etc). The high speed hits (braking bumps, roots, rocks, ruts) are controlled by the valving. This holds true for pretty much all suspension clickers, front and rear. Rebound adjustment can create some problems if not set close. The rear end can pack through whoop sections if it is set too stiff. It can make the back end kick if set too light. If a bike jumps consistently with the front end high, try setting the shock rebound setting a couple clicks softer. This will kick the rear end up a little on the lip of the jump making the front come down a little. Go out to a track you're familiar with and experiment a little. Just remember (write down) your beginning settings so you can always return there if you get things acting "not good". There are no "right" settings for any one model bike. Anyone who tells you that is just plain lying. I now some of you wanted to hear definite symptoms and how to cure them but it just isn't that simple. Too many variables. First thing to do is make sure the shock is freshly serviced and the pivots are working well and freshly greased. This is the starting point to cure any problems. MX Tuner