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Why Do My Fork Seals Keep Leaking?

Why Do My Fork Seals Keep Leaking?

If you see oil leaking from the motorcycle fork tube, do not ignore it since it can make riding uncomfortable. Motorcycle forks connect the front wheel to the frame through the steering assembly. The motorcycle fork tube also includes the front suspension and brake. The fork tube also plays a role in motorcycle handling and ensuring comfortable rides. If your fork tubes start leaking fork oil, damping will reduce, and the motorbike will become uncomfortable to ride. Read this article to learn why my fork seals keep leaking.


1. Understanding How Fork Tubes and Fork Seals Work

Understanding How Fork Tubes and Fork Seals Work

There are two types of fork tubes in the front fork assembly: the inner and outer tubes. Both tubes slide against each other and compress fluid inside them to ensure better shock absorption and wheel travel. The suspension’s wheel travel affects the amount of compression in the fork fluid.

Based on the type of fluid inside the motorcycle fork, there are two types of forks: oil and air forks. Both fluids store energy when compressed and release it when pressure is removed, ensuring better damping rates.

The fork oil seal is a simple rubber component that keeps the fluid inside the fork and prevents leaking. The fork seal needs to be tightly attached to the inner tube, leaving no room for fork oil to leak.

2. What Causes Fork Seals to Leak?

There are several reasons why a motorcycle fork starts leaking oil, including wear and tear, aging, and debris caught in the fork tubes. However, the most common reason why fork tubes start leaking fork oil is because of worn-out fork seals and debris trapped between the fork tubes and seals, providing openings for the fork oil to leak.

3. Debris Trapped Between the Fork Tube and Seal

Fork tubes and seals are rigidly affixed to keep the fork oil inside the tubes. However, debris can accumulate between the fork tubes and seals over time, resulting in small openings for the fork oil to leak. It often occurs in dirt and adventure bikes as there is continuous dropping, vigorous up-and-down movement of front forks, and hitting potholes and obstacles.

3.1 Difference Between the Fork Seals and Fork Dust Seals

The fork dust seal is the visible seal on the motorcycle fork that prevents dust from entering. It can be removed by using a screwdriver. Meanwhile, the fork seal is the inner seal not visible on the fork and stops fork oil from leaking. However, if it gets cracked, old, or worn out, the oil will start leaking from it.

3.2 How to Remove the Debris Trapped Between the Fork Tube and Seal

Fork oil leaks can be avoided by conducting regular inspections and maintenance checks. If there is dust trapped between the fork tube and seal, it can be removed using a Motion Pro seal mate.

  • Clean the fork tube using a dry cloth to remove dust
  • Remove the dust seal using a screwdriver and slide it up so you can insert the seal mate
  • Clean the leaked fork oil by wiping a dry cloth between the fork tube and fork seal
  • Also clean the dust seal to remove any accumulated dust
  • Insert the seal mate inside the fork tube
  • Force the seal mate to move between the fork tube and fork seal while pulling it up
  • After sliding the seal mate through the fork tube and fork seal, take it out. You should see the dust on the seal mate 
  • Wipe it off with a dry cloth and repeat the process
  • Repeat 3-4 times to completely remove the dust trapped between the fork tube and fork seal
  • Now sit on the motorbike and shift weight towards the front end to keep compressing the fork tube 
  • Clean the fork tubes again with a dry cloth
  • Put the dust seals back into their place

4. Old and Worn-Out Fork Seals

If you have not checked or replaced the fork seals, they will start leaking fork oil. The fork seals will wear out early if you ride a dirt or adventure bike since dropping the motorbike tends to happen more often. They also start wearing out early if you ride them in wet riding conditions. Cracks start to appear when the fork seals become old, resulting in oil leaks.

4.1 Replace Fork Seals

If your motorcycle has worn-out and old fork seals, you should replace them to avoid oil leaking from them. Fork seals are not expensive, but you may need to visit a professional mechanic to replace them since it requires disassembling the fork assembly.


5. Excessive Fork Oil

Fork oil helps improve the damping and rebound of the fork. The motorcycle owner's manual provides the recommended amount of fork oil. If there is excess oil is in the forks, the fork seals will start leaking when the forks compress due to dampening.

5.1 How to Fix It?

It is difficult to determine whether a motorcycle fork has excess oil. You should consult a mechanic since fixing this issue will require removing the fork assembly, draining the old fork oil completely, and refilling with new fork oil based on the information provided by the motorcycle owner’s manual.

6. Damaged Inner Tube

For the inner tube and fork seal to slide against each other smoothly without leaking fork oil, the inner tube must be smooth. Fork oil can also leak if the inner tube has scratches, cracks, and rust patches. Even if the fork seals are new, oil can still leak if the inner tubes are damaged.

6.1 How to Fix It?

To fix damaged inner tubes, you must first disassemble the fork assembly. Whether the inner tubes can be fixed depends on the severity of the damage. You can remove the rust patches by using WD-40 and cleaning it with lubricated abrasive paper. Make sure to use abrasive paper carefully to avoid scratching the inner tube’s surface.

If there are scratches on the inner tube causing fork oil to leak, treat the inner tube with chrome spray to make it smooth again. However, you will have to replace the forks if the damage is severe.

7. Air Leakage from the Motorcycle Air Forks Due To Built-Up Air Pressure

Some motorcycles are fitted with air forks, which are filled with air instead of oil to ensure shock absorption. The air shocks have valves to keep air pressure inside the forks at the atmospheric level. The air shocks are mostly found on dual sports and dirt bikes and require maintaining air pressure inside them for better damping rates. However, if the air pressure inside the forks increases above the recommended level according to the motorcycle owner’s manual, it can blow up the fork seal and cause air to leak.

7.1 How to Avoid This?

  • Before inflating the motorcycle air forks, the rider should confirm the required air pressure from the motorcycle owner’s manual.
  • Do not fill the air forks with too much air.
  • If you think the air pressure in the air forks is too high, release some air from the valve located on top of the motorcycle’s front forks.


8. Takeaway

The fork oil is essential for better damping and shock absorption. You should keep checking the fork oil level and refill it if it becomes low. You can check the recommended fork oil level on the motorcycle owner’s manual. The fork seal keeps the fork oil inside the inner tube. However, if the fork seal becomes old, cracked, and worn out, it can leak oil, resulting in bad front suspension performance and lower riding quality.

Fork tubes and seals require regular inspections and maintenance checks to avoid leakage. If the fork oil leaks, identify the reason for the leaks and take appropriate steps to fix them. If the damage is severe, you will need to replace the fork.

If your fork seals and tubes are in good shape, you can enjoy comfortable motorcycle rides. If you love going long-distance, there are several aftermarket parts available at Viking Bags, including sissy bars, handlebars, fairings, crash bars, backrests, and seats that can improve the ride quality and comfort of your motorbike. You can also choose from several luggage options available at Viking Bags, including saddlebags, sissy bar bags, and handlebar bags.

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