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Wednesday, April 4, 2012

Shocks: Changing Suspension Fork Fluid

The suspension in the front forks of a bike takes a lot of stress. All the weight of the rider and all the bumps and bounces of the terrain travel is dissipated through the front shocks. Most bikes have either spring or hydraulic suspension, but in both cases, suspension fluid is used to help keep things moving freely and dampen the load. As a result, the fluid can become tired and less effective, resulting in the need to replace it.

Failing to replace suspension fluid will make the ride too firm and can even lead to failure of the suspension, resulting in a costly rebuild or a claim from whatever company is responsible for insuring your bike. Fortunately, changing the fork suspension oil isn’t difficult to do, although it can vary from manufacturer to manufacturer, so it’s a good idea to check the guidelines on your shock supplier’s website. If you have an air sprung hydraulic suspension, it is also important to remember to release any pressure from the forks before attempting to replace any fluid, otherwise it could result in permanent damage to the suspension and even injury.

Manitou Suspension

Manitou forks have one of the most common types of suspension systems, and the process for changing the fluid is very similar to other makes, but it is always important to check manufacturer’s guidelines as some suspension systems do vary.

As with most bike maintenance, when attempting to replace the fluid, it’s always easier to start by turning the bike upside down before you remove the wheel and begin messing about with the suspension. Most bikes now have a quick release skewer, which makes things so much easier for getting the front wheel off. If your bike doesn’t, you need to remove the locking bolt where it connects to the fork ends.

Removing the Forks

Once you have the front wheel off, you will need to remove the brakes from the fork, which will require an Allen socket. A lot of brake cables are attached to the forks using cable ties, these will need to be cut off and replaced when you reattach the brakes. Next, remove the mounting clamp bolts on the top of each fork blade and then carefully remove the forks. Occasionally, the forks may be stuck with dirt deposits. If this is the case, gently use a rubber mallet to loosen them, and take this opportunity to give it all a good clean.

Use a socket wrench to unscrew the caps on the bottom of the fork legs. Be careful around the seals inside the forks and top lip of the forks as damage can cause leaks when you reassemble everything. At this stage, it’s a good idea to check the seals, because if they need replacing, now would be the time to do it.

Replacing the Fluid

Once you’ve removed the caps, place a bowl under the forks and turn them over to allow the fluid to drain out. Give the forks a gentle shake to get any stubborn fluid droplets out, but not so hard that you dislodge the seals. Now refill with the recommended amount of fluid. It’s important not to under or overfill, so check with Manitou’s guidelines for the particular forks on your bike.

Replace the caps on the end of the forks, and then slide the forks back into the mounting clamps. Tighten the mounting bolts back down, then slide the wheel back into the forks and tighten it back with the release skewer. Make sure you test the suspension play before taking the bike out, but if done correctly, there should be no problems.

Fox Forks

Fox forks are fast becoming mainstream suspension systems. More and more bikers are turning to them due to the quality and performance. However, this comes at a cost as the assembly of the suspension system varies greatly to other front fork systems. While the process for removing the forks is the same as for suspension systems such as Manitou, replacing the actual fluid in Fox forks is notoriously difficult.

The problem with Fox forks is that to change the suspension fluid you have to remove the lockout lever and red rebound adjuster on the shock absorber. For this, Fox sell specific damper removal tools, but caution still needs to be taken, as it is all too easy to turn the rebound damper past the end of its adjustment when you put it back on. If this happens, it can stick, which will require you to disassemble the entire damper system to get it unstuck. With Fox forks, it’s best to adjust the rebound to approximately the middle of its range and keep it there.

Another word of caution with Fox forks is to keep an eye on the little ball bearings inside the lockout lever, which are held in place by screws, and are very easily lost when taking apart the lockout lever. Fox do have a comprehensive guide on the Fox website to assist with any servicing, and the below video may also be of use:

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