A good hydraulic floor jack is a staple of every garage due to its versatile lifting abilities. With a floor jack there is no need to drive a car onto a lift -- simply put the jack underneath and raise it. For this reason, it can be a major frustration to find that your jack has broken. Fortunately you may be able to repair the jack yourself, and you should always try to do so before sending it away for a costly and potentially lengthy repair.
Compare the capacity on the jack to the weight of the vehicle. The vehicle's weight is listed on the driver's door pillar. The capacity of the jack is written on the jack or on the documentation that accompanied it when it was new.
Extend the piston by pumping it out or opening the release valve and pulling it out by hand. Watch for binding as the piston is extending. Once it is out look for dirt or grit on the piston which may have damaged the seal. Examine the seal at the bottom of the piston for pinches or cuts. If this seal is broken then the jack may have to go to a repair facility for further work.
Open the oil reservoir cap. This is usually the uppermost cap and you may need a flathead screwdriver to get to it. The oil should be 1/4-inch below the level of the hole. Top up the oil to this level if it is low and replace the cap.
Bleed air from the jack's hydraulics. Open the release valve and pump vigorously. Close the release valve, pump the piston to its full extension and then open the release valve to let it down. You should do this without using a vehicle as a weight. If the jack does not reach its full height then repeat the process until it does. Wipe the jack clean with a cloth before starting the bleed process and examine the jack afterward for evidence of leaks.
Lift the vehicle with the jack. If it still does not work then the pump may be broken and should be replaced. This is best undertaken by an authorised repair facility used to working with pressurised hydraulic systems.
Work on your jack in a clean, dry environment.
Never work under a vehicle supported only by a jack. Hydraulic fluid is flammable. Keep it away from flames.