How To Clean And Repair Leaking Fork Seals On Your Dirt Bike


The first thing you need to know about leaking fork seals is how to recognize you have them. This is easily done by checking the fork tube (inner tube) just below the dust seal. If it’s leaking you will see fork oil on the outside of the tube. If ignored, the oil will drain out of the fork, severely affecting its performance, which can also make the bike unsafe to ride.

Once spotted, leaking fork seals need to be replaced straight away, and you should ideally replace the oil and seals in both forks at the same time. If you don’t know how to do this your local bike mechanic will do it for less than $100 US.

Also, before you fix this problem, you’ll save yourself some headache by preventing it from having to fix it again later.  Spend $15 on some cheap seal savers from Amazon, and then go ahead and work on repairing the broken seal.

Causes of leaking fork seals

  • Wear & tear: The seals have a hell of a job of keeping dirt and crap out of the inside of the fork. They have a hard life but should last at least 40 hours riding time before they need changing. It depends on how and where you ride and how well you clean and maintain them. Every couple of years you should change the oil and seals regardless.
  • Imperfections on the inner tube: Stone chips, dents, scratches and elevations on the inner tubes will wear away the fork seals as they slide over them during use and cause them to leak prematurely. When changing the seals you should always check for imperfections and sand them off using very fine sandpaper (400 grit). Make sure you only sand using side to side motions – not up and down the fork.I had problems with my YZ 250 rhs front fork seal which was shitting itself every 8-10 hours. Turns out it had a number of small chips on the fork which can’t be sanded out 100% and may need re-chroming if it goes again. Joy.
  • Dirt, dust & grit caught inside: Your leaky seal may simply have some sand or dirt wedged between the fork seal and the inner tube causing an incomplete seal. In this case it is possible to repair it by carefully cleaning the muck out using a piece of film strip as explained below..

How to clean fork and dust seals

You should clean under the dust seals often especially after muddy, sandy or dusty conditions.

  • Carefully pry open the dust seal using a flat head screwdriver. Make sure you don’t damage the dust seal or scratch the fork by being too rough.
  • Use a clean (lint free) cloth over the tip of a small screwdriver to clean out any muck that is up under the lip. A Q-tip (cotton swab) seems to work well also.
  • Once it’s clean, push the dust seal firmly back in place using your fingers.

Tip: If mud is allowed to dry up on the fork tubes make sure you remove it before riding again as the crusty stuff will only wear away the seals.

That is all you need to do to clean ’em each time. But if you’ve just spotted a leak you can try this method before taking it to the shop. (This should only be attempted if there is already a leak – not as a precautionary measure.)

  1. Remove the dust seal.
  2. Using a piece of film strip carefully slide it up under the inner fork seal and move it up and down and around the circumference of the fork tube. The idea here is to extract any muck that may be caught in the seal so make sure you move the film in a forward direction with the top of the film at the front. You don’t want to force the muck deeper inside. 

If you think the fork has lost a fair bit of oil you should replace the oil and seal.

Tip: Next time you change the seals invest in a pair of seal savers to help keep the crap out. They’re cheap as chips and are brilliant for sand riders. In muddy conditions, it’s best to slide them up over the outer fork out of the way as they only tend to trap mud.

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Jim Harmer

I'm the co-owner of DBP. I live in Star, Idaho and enjoy dirt biking with my wife and two boys throughout the Idaho mountains.

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