Why Do My Fork Seals Keep Leaking?

That moment you see even the smallest trace of fork oil on your fork tube your heart sinks.  You know it is just a matter of time before you have a gusher springing from your fork seal.  This will cause your suspension to turn into a pogo stick with no damping.  This is not fast, nor is it safe.  To add salt to the wound, the fork oil can soak your front brake pads.  Now you have another safety issue, plus you have to add new brake pads to the suspension bill at the dealership.  Basically, something as simple as a leaky fork seal can ruin a ride or race day.

Fork seals leak from normal wear and tear, age, and debris getting into the seals. Imperfections and nicks in the chrome can also make your fork seals leak. However, the majority of the time your fork seals are leaking it's simply because debris is caught in the seal holding it open and allowing fork oil to sneak by.  

When you first notice the leak is the best time to take immediate action.  While you may be tempted to ignore it for now so you can keep racing, you know what will happen if you do ignore it. If you’re tearing out your hair, wondering why your fork seals keep leaking, read on to discover the issues and how to fix them so you can get back to racing quickly.

Index
1	How Do Fork Seals Work?
2	First, What To Look For
3	What Makes Seals Leak in the First Place?
4	What Can You Do to Fix Fork Seals?
5	Why Do Fork Seals Keep Leaking?
6	Conclusion

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How Do Fork Seals Work?

Modern motorcycle suspension is simply amazing. The amount of travel they have and the components inside controlling the speed of compression and rebound is all thanks to over 100 years of evolution in motorcycle design.

One reason today's suspension is so good is the use of oil as a speed controlling medium in the suspension. However, the challenge is keeping the oil where it belongs while also allowing the suspension to travel up and down thousands and thousands of times. The only component holding that oil in, even under high pressure during quick compression, is a tiny “lip” of rubber called the oil seal.

To bring it down to the basics, this tiny “lip” sits between the inner and outer fork tubes. As you can imagine, the connection between the inner fork tube and the oil seal needs to be perfect for it to prevent the oil from leaking. If the oil seal gets old or hard, it will no longer prevent the oil from leaking. Also, as described above, if something gets lodged in between the seal and the fork tube, it will allow oil to leak by.

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First, What To Look For

As mentioned above, look for oil on the fork tube around the fork seal. Sometimes the oil is hard to see, but don’t worry, the oil attracts dirt and soon you will see a dirty mess around your fork seal (traditional forks) or on the lower fork tube down toward your front axle (upside-down forks like on most modern motocross bikes). Basically, oil running down the fork tube should be your first clue that your fork seals are leaking.

Another obvious clue is when there is a puddle of oil under your forks, or your suspension just feels like an uncontrolled and bouncy spring. When enough oil leaks out, your bike becomes unsafe to ride. See can you ride with a bad fork seal for how far you can push it.

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What Makes Seals Leak in the First Place?

Seals Leak From Normal Wear and Tear

Seals take a lot of beating from normal use, and even more of a beating when ridden harder than normal. Dirt bike racing or riding off-road on dirt trails makes your seals work even more to keep the dirt and other junk out. Owner’s manuals put fork service on a regular schedule. For example, KTM’s 450 SX-F manual calls for a fork service every 45 hours, and Honda’s CRF450R manual calls for fresh fork oil about every 22.5 hours, both under average conditions. Check the manual for your bike. Seals usually get replaced when the fork is apart for service, and a good set should last at least 40 hours. Most people simply wait until they leak, but serious racers should be prepared and never let a leaky fork seal ruin a race day or their race results.

Even if you don’t ride your bike very often, plan on fresh fork oil and seals every couple of years, since seals can dry out and harden when a bike sits.

Dirt and Other Debris Can Get in the Seals

As already mentioned, dirt, sand, and other junk gets between the seal and inner fork tube, creating an incomplete seal. If that is what is happening, you need to clean them out following the methods described in the next section.

Inner Fork Tube Imperfections Can Cause Leakage

When riding, rocks and other debris will inevitably fly up and dent the inner tube or cause the fork to have scratches or chips. When this happens, it causes your seals to leak before they are worn out. You need to check the fork every so often to make sure this is not happening.

If it does, you can smooth the raised edge around the nick with a very fine stone or emery cloth on a block with light oil, working lightly in a “crosshatch” pattern, like honing a cylinder. You’re only taking off the raised edge; a low dent itself can’t be sanded out. If your fork tube had an imperfection it is likely it also damaged the fork seal.

You may need to fix the imperfection and replace your fork seal to fully correct the leak. If you only replace the fork seal, the imperfection in the fork tube will simply damage the new fork seal as well.

Be aware, however, that not all chips or dents can be smoothed out. If that happens to your bike, you may think about having a suspension shop re-chrome the fork tube, or replace it.

Extended Pressure from Tie Down straps

Those poor fork seals already take enough abuse, and then if you use a tie-down system that compresses the front forks when you are transporting you are putting a constant source of tension on the fork seals. Straps on the handlebars hold the bike by compressing the front suspension, so the forks carry most of the load. Check out Risk Racing Lock-N-Load Systems: they hold the bike by the footpegs, so the load is shared between the front and rear suspension and there’s far less pressure on your fork seals, aside from making your life easier transporting your bike(s).

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What Can You Do to Fix Fork Seals?

Aside from replacing the seals, there are several things you can do to fix your fork seals and be racing again before you know it. For a step-by-step guide, see how to fix leaking fork seals on a dirt bike. If you cannot do it yourself, you should take your bike to a qualified bike mechanic to do it for you. Replacing fork seals at a shop typically costs between $200 and $400, depending on how many parts need to be replaced.

Lift the Dust Cover and Clean Underneath Them

If you know what you’re doing, carefully pry apart the dust seal using a flathead screwdriver while being careful not to scratch the fork or damage the seal. Using a lint-free cloth, clean out any mud or debris stuck under the lip before putting everything back together again.

If that doesn’t take care of the problem, remove the dust seal and use a piece of camera film or another flexible thin object to wrap around the shaft, then push up until you get under the lip. Using this method can get out debris that a cloth might miss. Then put everything back.

The film trick works, but it’s fiddly, and anything stiff or sharp can tear the seal lip. The Seal Doctor is designed to pull the dirt out of the seal rather than push it deeper.

Use the Seal Doctor on the Fork

Leaks happen almost anywhere at the worst times, like when you’re at the track or hitting the trails, and having the proper tools to quickly fix a leaky fork seal can save the day. The Seal Doctor by Risk Racing is the tool made for exactly this job: it pulls the dirt out of the seal so the leak stops. Vital MX and Dirt Bike Magazine both tested the Seal Doctor and gave it positive reviews.

Just lower your dust seal and snap the Seal Doctor on your fork tube, insert the tooth into the leaky seal and twist. The design of the Seal Doctor maintains the proper position and angle as you rotate around your fork tube. The bottom of the Seal Doctor has a second tooth design to clean your dust seal. Wipe the fork clean and put the dust seal back when you’re done.

The patented Seal Doctor also comes with a protective holder so that it can be stored safely in your toolbox or trail pack ensuring you always have the appropriate tool for the job. Cleaning works when debris is the problem; a seal that is torn or worn out still needs to be replaced.

Replace Fork Seals

Fork seals wear out eventually and leak no matter what you do to keep a tight seal, even if you regularly clean them. If you don’t know how to replace them, you may want to take it to your local bike mechanic or become pals with a mechanically inclined moto-buddy and learn closely.

You will need specialty tools, like fork seal drivers, to complete the job on your own. These tools can be expensive and specific to your bike or suspension size. A trip to the dealership to fix this issue costs money too. The quickest option would be to start with the Risk Racing Seal Doctor and see if cleaning stops the leak before you replace anything.

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Why Do Fork Seals Keep Leaking?

You’ve done everything you can to fix the fork seals, yet they still leak. This can be very frustrating, but for your own safety, it is important that you get it fixed properly.

Fork Seals Leaking After Replacement? They May Not Be Installed Correctly

If the fork seal leaks immediately after replacing with a new fork seal, the issue is probably improper installation of the new fork seal. Often, the sharp edges on the fork tube can cut the delicate seal during installation. An experienced mechanic covers the end of the tube with a seal bullet (a plastic sleeve over the sharp edges) or a thin piece of plastic and puts a light coat of fork oil on the seal lip before sliding it on, then seats it squarely with a seal driver. A seal that goes in crooked, or a retaining clip that isn’t fully seated, will leak too.

Fork Seals Are Not Completely Cleaned

If the above doesn’t stop the leak, you may want to recheck the seals, as they may not be completely clean. Even a small speck of dirt can cause the oil to leak through. Repeat the cleaning process until you are sure you have cleaned everything out from under the seals.

Once you have the seals cleaned, be sure to wipe all the dirt and bugs from the fork after every ride.

There Are Nicks in the Chrome Under the Seal

Stones and other debris can fly up and nick the chrome under the seal, creating small raised edges that let small amounts of oil leak through. The best way to take care of that is to use a very fine stone or emery cloth to smooth the raised edge of the nick. However, some damage can’t be smoothed out. In that case, you may need to re-chrome or replace the fork tube.

Haul your bike differently

If you keep getting recurring fork seal leaks after repair or replacement, look at how you transport the bike, and consider skipping handlebar tie-down straps. The Lock-N-Load or Lock-N-Load Pro Moto Transport Systems hold the bike by the footpegs while reducing the stress on your fork seals.

Consider the Conditions You Ride In or Install Additional Protection

If you ride in sandy or muddy conditions you will be more prone to fork seal contamination. You can install special neoprene fork seal covers to keep contaminants away from your fork seals.

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Conclusion

That first trace of oil on your fork tube doesn’t have to end your ride. Fork seals are finicky things and need regular care to avoid leaks, and often the leak is just dirt holding the seal open. If you follow the suggestions in this article and your fork seals still leak, you may need new seals or a new fork tube. Take the bike to your mechanic to look it over and find the cause.

Before you get there, try the Seal Doctor. It pulls the debris out of the seal quickly and easily, and it comes in two sizes, one for 35 to 45 mm fork tubes and one for 45 to 55 mm, which covers most dirt bikes and most street bikes too. Check your fork tube diameter before you order.

If you keep your fork seals in top shape, you can enjoy racing for many years with the same bike.

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