Shock absorber maintenance

From Wiki

Adding fluid to the shocks. Here is the check: Stand the shock on the floor with the shaft end up. With a rag or some kind of pad under your hand, push the shaft down from fully extended, it should go very easy the first 3/4". Then there is resistance from the oil and piston to half way down or 3" of travel. Then the springs inside start to resist, but you should be able to put your full weight on it to compress fully. If it is out of oil or low, the top 3" will not restrict the shaft movement. It will move quick and easily.

To simply add oil, remove the snap ring, and the main seal cap. This is the current style - some old style boats with hull number up to 35 or so may have two screws going into the side of the tube and a short ways into the Delrin cap if you haven't upgraded. Stand the shock up and pull up the shaft, don't pull the rod out any farther than absolutely necessary to pour oil in or the remaining oil will drain out the bottom internally. Add ATF (automotive automatic transmission fluid) to a level of 1.5" from the top (approximately 3 ounces total). This creates an air gap inside of about 3/4". Reassemble the main seal end cap and snap ring or two screws for older models.

Note: Pumping the shaft up and down slowly to get oil into the chamber below the piston may be required if low or empty. If they are so low on fluid, there is likely a very worn O-ring and should then be taken completely apart and change all O-rings.

The O-rings are off-the-shelf rings that can be bought at a specialty shop. 3/8 x .063 and ¾ x .125 inches. Due to tolerance stack up, I have found that a metric O-ring fits better in most cases. The size is 2 x 8 millimeter.