How to Rebuild a Hydraulic Jack


Hydraulic jacks are relatively simple machines. If you have one in your workshop that no longer lifts, then you should consider trying to rebuild it. Many jacks are designed to be disposable and thrown out as soon as they break, but high quality hydraulic jacks can be rebuild instead of being replaced and some manufacturers offer rebuild kits. The procedure is the same whether you have a bottle jack or a floor jack. A floor jack has a bottle jack inside, so remove the bottle before starting the procedure. This procedure should not be part of your routine maintenance routine but it may help if the jack is not working correctly.

Things You'll Need

  • Socket set
  • Screwdriver
  • Pencil magnet
  • Pipe wrench
  • Rebuild kit or spare o-rings and washers
  • Hydraulic oil
  • Cloth
  • Drain the oil from the jack by removing the drain plug. This is usually the uppermost plug if the bottle were standing on its base. Once the oil is drained, clean and replace the drain plug.

  • Remove the handle assembly. This is usually held in place by a few bolts. Once you have it off, pull the pump piston out from underneath the handle. This can be done by hand, though you may want to secure the jack with a vise.

  • Remove the release valve by unscrewing it. There is usually a ball or pin to regulate flow under the cap. Remove this by using the pencil magnet and keep the ball and cap together.

  • Remove the overload valve. This valve is often under a screw and close to the release valve. Remove the screw or bolt holding it in place and then use the pencil magnet to remove the two balls and springs underneath. There may also be some dividers, plates and guides underneath it. As you remove these, make a note of the order they were removed. This will help you when it comes to replacing them.

  • Use the pipe wrench to remove the tank nut from the top of the bottle. Once this is off, the piston will slide out and you will be able to slide all the pieces apart. Make another note of which piece was inside which, so you can put them back together afterward.

  • Examine all the o-rings and seals for pinches, cracks or breaks while everything is apart. Replace the o-rings and washers with new ones. When removing the o-rings do not use the side that creates the seal as leverage as this may damage the surface and prevent the new ring from sealing correctly. You can also soak the new soft o-rings and washers in hydraulic oil to improve their initial seal.

  • Reassemble the piston by referring to the directions you drew up when you removed it. Slide the piston back inside the bottle and tighten the tank nut.

  • Replace the balls and springs in the overload valve. Usually the smallest ball goes first, followed by the smaller spring and then the large ball and large spring. Refer to the directions you wrote when removing them if you have additional parts. Replace the cap on the top of the hole.

  • Replace the ball or pin inside the release valve by dropping it in to place and then replace the release valve screw or bolt.

  • Push the pump piston back into place under the handle and replace the handle assembly using the bolts you removed earlier to secure it in place.

  • Open the oil reservoir cap, refill the jack with oil and bleed any excess air from the system. To bleed the air, open the release valve and pump the handle vigorously several times. Then close the vale, pump the jack to its full height, open the release valve and let it down. Repeat this process until the jack reaches its full height.

  • Wipe the jack all over with the cloth and test it by lifting a vehicle. Carefully examine it following the test for any evidence of leaks.

Tips & Warnings

  • Make sure your work area is spotless. Dirt and grime will destroy the inside of a jack.
  • Before starting to rebuild a jack check the price of a new model. Sometimes the rebuild kit costs more than a comparable new jack.
  • Never work under a vehicle supported by a jack alone. Always use jack stands.
  • Hydraulic fluid is flammable, keep it away from open flames.

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  • Photo Credit fallen jack stand image by Joyce Wilkes from
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