Actually, shocks are easier to service than forks, and really do not require any special equipment that you cannot just make. I service my shocks often enough that I purchased a nitrogen tank that just lives in the race van.
Here are some important considerations:
1. Once you have your shock on the bench, measure the spring from top to bottom before you touch the tension nuts. This will help you be able to reset the spring to the same preload when you put it back together. The best thing to have is a spring removal tool that allows you to just remove the spring without touching the nuts, but most folks do not have this tool. With the measuring process, you do not have to have the tool. Simply loosen the nuts to the point that you can remove the spring. I?ll assume you can manage this. If not, do not continue, as you might not have the necessary mechanical skills to accomplish a shock service.
2. Put the shock upside down into a vice. Use a rag on the vice jaws to ensure you do not damage the shock body.
3. Once you release the nitrogen from the bladder, you will need to depress the bladder cap in order to expose the snap ring. You might need to take a large socket, place on the cap, and tap gently. You only need to depress the cap about 1/2 inch, then reach in with a dental tool or small flat blade and remove the snap ring. Be careful not to scratch the inside of the shock body, as this is where the o-ring seals.
4. Once the snap ring is out you will need the use a special tool (resembling a small slide hammer) to remove the cap. To make the special tool, you will need a 3/8 inch bolt about 6 inches long, a could of large washers, a couple of 3/8 inch washers, a 3/8 inch lock nut, a large nut (something on the order of 1 inch), and a metal valve stem cap. Put one large washer on the bolt (you may need to use a smaller washer first to keep the large washer from slipping over the head of the bolt), then the large nut, the last large washer (followed by a small washer if one was require on the top), and finally the lock nut. Tighten the lock nut so it is on the bolt about one inch. Grind the top off your metal valve stem cap, and grind the bolt at the bottom so it is a small enough to allow the ground end of the cap to just fit on the bolt. Solder the cap on the bottom of the bolt. You now have a slide hammer the will screw on the valve of the bladder cap. Screw in on until it stops, and gently slide the large nut back against the washers until the bladder cap is all the way out of the shock body.
5. The valve/rod side of the shock is held together with the same type snap ring, so all you need to do is pop the dust cover off (I use a zip tie on the shaft to hold the dust cover up the shaft). Push down on the shock seal with two large screwdrivers using even pressure, and you will expose the snap ring. You will need to open both needle valves to help move the oil through the shock body as you push down on the valve. Once the snap ring is out, wiggle the shock shaft and the shock seal and valve will come free.
6. With the body now empty of all parts, clean out all oil. I use spray carb cleaner to get everything out, and then a clean rag to wipe everything clean. I also blow air through the passages to make sure they are clear.
7. Filling with oil is tricky. Fill the bladder side first about 1/2 full, and put your mouth on the opening. Blow into the body, pushing some oil though the passage into the other side of the body. This will eliminate trapped air in the passage between the two sections of the body. Get ready, your about to make a mess. I tie a couple of rags around the shock body to help catch as much oil as possible. Put the clean bladder on the cap, screw on your special tool, and slide the bladder into the body using a wiggle motion. You want oil to come out of the shock, as this will ensure that there is not any trapped air. Push the bladder cap just below the snap ring groove, and put the snap ring in place. Pull the cap up against the snap ring, and remove the special tool.
8. Turn your attention to the valve/shaft assembly. Fill this side all the way up with oil, and gently slide the cleaned valve into the body. Oil is going to come out. Also, do not let the shock seal fall into place yet. Wiggle the valve into the oil all the way to the bottom. You will see air come to the top of the oil. Once it is all the way down, wiggle SLOWLY upward. Do not allow the valve to come out of the oil, as you will have to start over. Repeat this up and down process several times until there is no more air coming to the top. You might have to add more oil during the process. Air is the enemy, so get it all out.
9. Once all the air is out, push the shock seal down into the body. It will not go down all the way, but while applying pressure, loosen the Allen screw at the top of the shock. (the part in the vice jaws). This will allow a small amount of oil to come out, and help the seal slip into place. Do not let too much oil out, just a little to release the pressure keeping you from seating the seal. Once the seal drops into the body, slide in the snap ring into the body, and follow the seal down with the snap ring. You do not want the seal to drop any lower than required to install the snap ring. As you get close to the snap ring groove, tighten the Allen screw you loosened earlier to relieve some pressure. This will ensure you do not let too much oil out.
10. Install dust cap, and clean the excess oil off the floor, bench, shoes, etc. Have someone pressurize the bladder with about 150 pounds of nitrogen, and install the spring to the right measurement. Also, don?t forget to reset the compression and rebound needles to their original settings.
11. One last note. Do not use fork oil, no matter what the guy at the parts counter says. Use "suspension" fluid. Most fork oils are not rated to handle the high heat produced by the shock. Don't think it gets hotter than the forks? Next time you ride, stop, take your glove off, and grab the fork. No problem. Now grab the shock. Hmmm, what an education.
Once you get good at the process, it should take about 30 minutes, but the first time will take a few hours. Have fun with the project. Let us know how it turns out. If you?re concerned about reassembly, set a video camera on the bench.
Rick
