Office chairs are invaluable tools that often go unnoticed in our daily work. When functioning correctly, they require no attention, but when they begin to malfunction, they're a distraction and an annoyance. Luckily, repairing an office chair isn't too difficult, since most have similar, limited functions. Though there are many different mechanisms and devices that operate chairs, the basic functions fall under a few basic categories: seat height, rolling and rocking.
Diagnose the main category of the problem with the chair. For seat height issues, you'll look for the chair raising and/or lowering at the wrong times, or not raising at all. For rolling issues, you'll look for hesitant rolling, sticking, or leaning. For rocking issues, you'll look for the seat rocking when no one's sitting in it, leaning with no one in it, or rocking when the lock that should prevent rocking is engaged.
Flip the chair over, so the bottom faces up. Unscrew (or unbolt depending on your specific chair construction) the base and piston mechanism from the seat bottom. Replace the screws (or bolts) in the seat bottom and set it aside.
Examine the base and cylinder mechanisms. Look for bending, wearing and broken pieces. Height adjustment issues will relate to the cylinder and lever mechanism. Rolling issues will relate to the casters and caster arms on the base. Rocking issues will relate to the mounting plate between the seat and the cylinder.
Adjust any bent pieces that might affect the working of the cylinder. If the control lever is bent, you may need to bend it back by gripping the arm with the Stillson wrench and slowly bending it back into shape. If the problem is with the cylinder not holding pressure, then it will need to be replaced.
Flip the base and cylinder so you're looking at the bottom of the base. Pry up and twist the clip over the bolt head at the base of the cylinder. Remove the washer and slide the base off the cylinder.
Unscrew the cylinder from the seat plate and remove it. Insert a replacement cylinder and attach it to the seat plate and the base. Re-clip the cylinder to the base with the clip and washer in place. Screw the chair back to the seat plate.
Look for dirty or corroded casters. The most common problem with casters is that they're filled up with dirt and hair. Use the screwdriver and pliers to pull out any dirt and gunk in the wheels. Spray on lubricant to break up any corrosion and allow the wheels to turn and spin smoothly.
Remove any broken or bent casters. Unscrew (or unbolt) the mounting on the top side of the caster arms and slide the caster out the bottom. Replace the casters with new ones and screw them back into place.
Replace the base if one or more of the caster arms are bent, preventing the chair from rolling smoothly. Remove the screw (or nut) for each caster and remove it. Remove the cylinder from the base and install the new base. Attach the cylinder washer and clip to the base and screw (or bolt) each of the casters into place.
Examine the seat plate for bends or breaks in the lever mechanism. Also look at the bottom of the seat, to see if the screw holes have been worn away so the seat plate cannot mount securely to the seat bottom. If the rocking mechanism is broken, you'll need to replace it. If the seat plate is slightly bent, or the mounting holes are worn, you can still repair it.
Hammer the bent part of the seat plate against a hard, flat surface to bend it back straight. Check your progress after every other hammer blow, to make sure you aren't bending it too far. Re-mount the seat plate to the seat bottom with the screws.
Cut the 1.8 cm (3/4 inch) plywood to a size one inch larger than the bottom of the seat plate, on each side. For example, if your seat plate is 7.5 by 7.5 cm (3 by 3 inches, you'd cut the plywood to 10 cm by 10 cm (4 by 4 inches). Drill through the plywood into the seat bottom with the plywood piece centred on the seat. Screw the plywood into place, then drill through the holes of the seat plate into the plywood and then screw the seat plate to the plywood.