To repair a Walker floor jack, clean the floor jack, pry the plug off the cylinder, drain hydraulic fluid, fill the jack with fresh fluid, and mount the plug back in place. Pump the lifting arm several times to work the fluid through the jack. Carefully test the jack. Fresh hydraulic fluid, a funnel, a flathead screwdriver and shop rags are necessary for the repair.
Place the jack on a solid work surface, and use clamps or heavy items to hold it in place. Clean debris off the jack's cylinder with a shop rag. Pry off the circular plug with a flat-bladed screwdriver, taking care not to mar it. Place a drain pan under the jack, lower the jack slowly to drain out fluid, and then carefully stand it back on the working surface. Blow persistent debris off the chamber with compressed air.
Follow the manufacturer's recommendation to fill the jack with new fluid, using a funnel as a guide. Use 5W-30 motor oil temporarily if you don't have hydraulic fluid. Wipe down the plug with a clean rag, and mount it on the cylinder. Sit the plug on the cylinder properly to avoid leakages. Ensure that you use a new plug if the old one is damaged.
Wipe excess fluid off the jack. Raise and lower the jack several times to be sure it is working properly. Order a new cylinder online, and replace it if necessary.