The forks of a motorcycle are one of the most important parts for safety, handling, and general operation of the motorcycle. These forks connect the frame to the front wheel, and since many motorcycles have a 50/50 weight distribution, they under a heavy load. Proper functioning fork seals are critical to maintaining your motorcycle.
Fork seals aren’t just important for maintaining the mechanical components of the motorcycle, its also important for safety. Leaky fork seals could leak oil on the front brakes. This will result in trouble stopping and mess up the shock absorption on the motorcycle.
All of these factors make it dangerous to ride a motorcycle with bad or leaking fork seals. Despite this fork seals are often the most neglected part of a motorcycle. So how do you know when it’s time to replace fork seals? However, before we discuss that, lets go over what the fork seal does.
What is the Purpose of a Fork Seal
The forks of the motorcycle are what attach the motorcycle frame to the front wheel. Usually the motorcycle will have a triple clamp. The center clamp will attach to the motorcycle frame while the other two clamps will attach to the forks.
The front forks support up to 50% of the motorcycle’s weight and even more under hard braking. The forks are filled with oil and a spring to absorb impacts from the road or jumps (if its a dirt bike). The oil acts as a dampener. It reduces the speed of the fork compression when the motorcycle hits a bump. The fork seal’s function is to keep the oil inside the fork.
Why Do Fork Seals Fail?
There are several possible causes for fork seal failures. The first and probably least common is physical damage to the seal. This can be caused by accidents, rocks, or really anything impacting the fork seal.
The next factor is age. All seals deteriorate with time and fork seals are no different. Its important to check the condition of the fork seals ever so often so that you can replace them before they cause a problem.
The last and most common reason for fork seal failures is dirt and debris getting on the forks and wearing out the seals. Many times the seal is still intact but dirt or debris is in-between the fork and the seal. This allows a leak path for oil which can lead to problems with your suspension. Before you tear your bike apart replacing the fork seals, give this trick a try with a 35mm camera lense.
So what are the signs that the fork seals are bad?
Bad fork seals leak oil. The oil that leaks will follow the forks down to the front wheel. The front wheel just happens to be attached to the front brakes. Since brakes use friction to stop and since oil is a lubricant which reduces friction, you can see how this is a bad combination.
This can basically reduce any braking affect from your front brake. Under normal riding conditions, the majority of the braking load is done by the front wheel. Without the front brake the stopping capabilities of the bike are severely limited.
Reduced Shock Absorbstion
In a suspension setup oil provides damping and the spring provides the force to return the suspension to equilibrium. If a suspension only had a spring, it would oscillate up and down over and over again after hitting a bump.
This is where the oil comes in. The oil provides damping so that the suspension only compresses once and then the spring forces it bake to its equilibrium ride height position.
A bad fork seal will allow the oil to leak out of the forks. This takes away the damping in the motorcycle. After going over a bump the motorcycle’s front fork will oscillate up and down. This creates a dangerous handling situation.
Another possible situation is that only one of the fork seals is bad. This will cause an even more dangerous handling situation because half of your front suspension will not be adequately damped.
The motorcycle will be difficult to control when hitting potholes especially while cornering. This will make handling and steering extremely difficult. If you notice any of these handling attributes you should check your fork seals right away. Feel around the front forks to see if they are wet with oil. That is a dead giveaway of a fork seal failure.
How Long Do Fork Seals Last?
Motorcycle fork seal life can vary a lot by the top of riding you do. Offroad dirt bike’s go through fork seals much faster than cruisers. Dirt bike fork seals last for approximately 20-80 hours of riding. On a street bike its more likely that the fork seals will fail from age than miles.
As you can see its not a good idea to ride a motorcycle with bad fork seals. It can be very dangerous as it can take out your front brakes. A leak that has gone on for a long time can cause suspension and handling problems. Its never a good idea to ride a motorcycle without proper functioning front forks.