How to Change the Oil in MTB Suspension Forks

A mountain bike (MTB) front fork holds the front wheel and allows the rider to steer and balance the bicycle. As of 2011, most mountain bikes come with a suspension fork, which uses either a spring mechanism or air hydraulics to cushion the bike when going over rough terrain or dropping from heights. Eventually, like all mountain bike parts, the fork will need serviced. This can be as simple as removing the dirt from the legs (stanchions) and lubricating the seals. However, if this does not fix the problem, it may be time to disassemble the fork and change the oil.

Things You'll Need

  • Allen/hex key set
  • Rubber mallet
  • Fork oil
  • Fork air pump (hydraulic forks only)
  • Old rag
  • Spanner wrench
  • Bike lubricant
  • Bowl
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Instructions

    • 1

      Place the bike on a stand. Using the Allen keys remove the brake calipers from the fork.

    • 2

      Place a bowl under the fork and remove the bolts from the bottom. The oil will begin to bleed from the bottom. If your fork does not have bolts on the bottom, check its user manual. Some fork bolts are accessed internally. Use an old rag to mop up any spilled oil and any residual oil on the outside of the fork.

    • 3

      Slide the housing of the fork legs off the fork. If there is some resistance, use a rubber mallet on the top of the fork leg's connecting top arch to loosen it. Clean the lower revealed portions of the legs. Don't use paper towels or anything that will fall apart and stick inside. Clean carefully around the seals and top lip of the fork, checking for any scratches, or nicks out of the seals and use a flashlight to check that you've got all the dirt and grit out.

    • 4

      Remove the top cap from the spring of the fork using a tightly fitting spanner. Pour out any residual old oil. Remove the spring, making a note of which leg each spring has come from and how the fit together. If you've got an air fork, clean gently around all the plunger and seal sections and wipe the inside of the air chambers.

    • 5

      With the fork and bike upside down replace the oil in the fork legs, making sure you adhere to your fork manufacturer's guidelines. Changing the amount of fluid or its weight can cause big changes, ranging from altered damping performance to complete hydraulic lock.

    • 6

      Re-assemble the fork carefully by performing the above steps in reverse, lubricating any seals to reduce friction. Check that the fork is operating smoothly before taking it on a long ride.