What causes fork seals to leak?

Suspension on a dirt bike takes a pounding and it's only a matter of time until the fork seals leak. If you are a serious dirt biker, you can count on fork seal related maintenance as part of your regimen. No matter how likely fork seal replacement may be at some point, it is important to realize that there are many possible causes of leaking fork seals.

  • Failed seal
    • The constant motion of the forks can wear the seal lip enough that the lip of the seal can no longer seal against the fork tube.
    • A broken or stretched seal coil spring (the spring that is wrapped around the seal lip diameter) will result in a relaxed seal grip on the fork tube, facilitating leakage.
    • Seal material can be damaged as a result of harsh riding conditions, fork mechanical problems or improper assembly.
    • Seal material can fail by age (erosion the lip of the seal).
    • Contact with chemicals that the seal material is not compatible with, which may cause hardening, softening or deformation.
  • Seal installation problems
    • Seal retaining clip not fully seated in clip groove or is dislodged from the groove completely. This allows the seal to float around in the seal bore, which will likely result in leaking.
    • Seal not mounted squarely in fork tube. A seal will not seal properly unless it is fitted accurately. Because a seal is primarily made of an elastic material, it is possible to have a secure fit while being crooked.
    • Missing back-up ring, if applicable. In many designs, a steel back-up ring is mounted behind the oil seal. If the back-up ring is missing, the seal can move in the seal bore, which will likely result in leaking.
  • Debris under the seal lip
    • A failed or worn dust seal will allow dirt to infiltrate the oil seal. Dirt will eventually push into the oil seal lip, causing a leak.
    • Fork alignment problems can open the sealing surface during fork movement, allowing material into the sealing area.
  • Fork alignment problems
    • Fork tubes not in alignment due to improper front wheel mounting. Improper wheel mounting can cause the fork tubes to be out of parallel with each other.
    • Fork tubes not in alignment due to triple clamp problems. With a hard impact or crash, the fork tubes can be twisted in the triple clamps, causing the forks to be out of parallel with each other.
    • Fork tubes not equal in mounting height.
  • Fork damage
    • Bent fork tube(s).
    • Inner fork tube surface severely worn, scratched, dented or pitted.
    • Inner fork tube out of round.
    • Fork slider bushings badly worn. Seals can open when there is sloppy fit between inner and outer fork tubes.

PARTS AND SUPPLIES

Need parts and supplies for your dirt bike? We have you covered with all the parts and accessories you need from aftermarket to OEM.

FRONT SUSPENSION TUNING

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FORK BLEEDERS

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FORK BUSHINGS

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FORK SEALS

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SUSPENSION FLUIDS

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REAR LINKAGE BEARINGS AND SEALS

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REAR SHOCK REPAIR PARTS

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SPRINGS

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