How to Rebuild Hydraulic Jacks

Hydraulic jacks are essential tools in any auto repair shop. Like all tools, they can wear out. In most hydraulic jacks the seals wear out first, causing oil to leak from the jack and the jack to stop lifting. Sometimes this problem can be fixed by thoroughly rebuilding the jack and replacing the seals. The procedure is the same whether you have a bottle jack or a floor jack. Floor jacks have a bottle jack inside them, so take it out before starting the procedure.

Things You'll Need

  • Screwdrivers
  • Wrench set
  • Pencil magnet
  • Pipe wrench
  • Rebuild kit or o-rings
  • Hydraulic oil
  • Cloth


    • 1

      Drain the oil from the jack by opening the oil reservoir cap and draining out as much as you can. Bear in mind that there may still be oil in other parts of the jack.

    • 2

      Remove the handle assembly by unbolting it. There are usually two or three bolts involved and the process will vary depending on the type of jack you are working with. You will be able to skip this step with some floor jacks. Remove the pump piston by pulling it out. It should come out with some pulling. The best option is to put the jack in a vice.

    • 3

      Remove the release valve by unscrewing the cap. There is a ball or pin underneath. Use the pencil magnet to lift this out.

    • 4

      Remove the overload valve. This is usually located close to the release valve. Unscrew the cap and remove it. Inside are usually two balls and two springs. Remove these with the pencil magnet and record the order in which they came out.

    • 5

      Remove the tank nut with the pipe wrench. The tank nut is the nut at the top of the bottle. Once this has been removed the piston will be loose and the parts should slide apart. Make a note of what slides out of what so that they can be put back together in the same order.

    • 6

      Examine all the o-rings and washers for pinches, breaks and caps. Replace those that need replacing. When you lever the seals from the metal parts make sure you lever away from the sealing surface, otherwise you may damage the sealing surface and compromise the seal. It may help with the initial seal if you soak all the soft o-rings and washers in hydraulic oil before putting them in place.

    • 7

      Slide the parts of the piston back together, using your notes for reference. Slide the piston back into the bottle and secure it with the tank nut.

    • 8

      Replace the overload valve. Replace the balls and springs using your notes to give you the order, although the normal order is the small, then the smaller, spring, and then the large ball and the large spring. Reference your notes for the position of the guides, plates and anything else.

    • 9

      Replace the release valve. Drop the ball or pin into place and replace the cap.

    • 10

      Replace the pump piston by pushing it back into its place. Replace any parts of the handle assembly you removed to get to the pump piston.

    • 11

      Put the oil back into the reservoir and top the oil up to about 1/4-inch below the hole when holding the jack horizontally. Bleed air from the system by closing the oil reservoir, pumping the handle vigorously with the release valve open and then raising and lowering the jack normally. If the jack does not reach its full height, repeat the bleed process until it does.

    • 12

      Test the jack by lifting a load. Wipe the jack with the cloth before starting the lift and check the outside after the lift for evidence of any leaks.

Tips & Warnings

  • Make sure your work area is as clean as possible before starting work. Dirt and grit will destroy the jack if they get inside.
  • Before purchasing a rebuild kit check the price of a new jack --- sometimes a comparable replacement jack costs less than a rebuild kit.
  • Never work under a car supported by a jack alone.
  • Hydraulic fluid is flammable. Keep away from flames.
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  • Photo Credit fallen jack stand image by Joyce Wilkes from

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