19/12/2017
Following a rear shock rebuild, it's only logical to turn our attention to the front forks of your DR350. Often perceived as more straightforward than their rear counterparts, a front fork overhaul can significantly improve your bike's handling and ride comfort. Let's get those DR front forks performing at their peak once again.
What You'll Need for the DR350 Front Fork Rebuild
Before diving in, ensure you have the necessary components and tools. A successful rebuild hinges on having the right parts and equipment readily available.
Essential Parts:
- Just over 1 litre of 10W fork oil
- New dust seals
- Fork bushing kit
- Fork boots
Necessary Tools:
- Various screwdrivers
- A basic set of socket wrenches
- An impact wrench (highly recommended)
- Measuring tape or callipers
- Zip ties
- A hammer
- A thin, rigid object (like an old knife or pick)
- Pliers
Having these items on hand will streamline the process and prevent frustrating interruptions.
Disassembling the DR350 Front Forks
The disassembly process is methodical. Start by removing the fork boots to gain access to the main components.
Begin by loosening the two clamps securing the fork boot. Typically, this involves unscrewing a single bolt on each clamp. Once the bolts are removed, the fork boot can be pulled off.
Next, you'll need to unscrew the fork cap. This can be challenging if you don't have an impact wrench. If you lack this tool, it's advisable to leave the fork mounted to the triple clamp on the bike and attempt to unscrew the cap with a socket wrench by hand. However, an impact wrench makes this task considerably easier.
With the fork cap loosened, the internal spring can be removed. It should slide out without much resistance.
Once the spring is out, carefully drain the old, often discoloured, fork oil. You can help remove any residual oil by sliding the fork stanchion up and down.
Locate and remove the rubber cap that covers the damping adjuster. A screwdriver is useful for prying this off.
The next step is to remove the damping rod bolt, which also serves as the adjuster. An impact wrench is again very helpful here.
With the bolt removed, the damping rod inside the fork should become free. If it seems stuck, try sliding the fork stanchion up and down a few times to dislodge it.
Once the damping rod is free, it can be carefully removed.
With the damping rod out, you can now remove the dust seal. This is done by carefully inserting a thin, rigid object (like an old knife) between the seal and the fork slider. Gently tap the object with a hammer, working your way around the seal and rotating the fork. Switch to a screwdriver as you gain more space, continuing to pry gently until the seal pops out.
Beneath the dust seal, you'll find a snap ring seated in a groove. Use a small, flat screwdriver to carefully prise this snap ring out.
To separate the fork tube from the fork slider, you'll need to pull them apart forcefully a couple of times. This action should release the fork tube, along with two bushings, a washer, and the oil seal.
Inside the fork tube, you may find a damping rod spacer. It's important to note this part for reassembly.
Now, you can disassemble the parts from the fork tube: slide off the oil seal, washer, and one of the bushings.
The second bushing can be removed by slightly prying it open with a screwdriver.
Inspect your bushings carefully. Worn bushings with damaged coatings can potentially scratch the fork tubes, necessitating their replacement.
The final component to disassemble is the preload adjuster.
After disassembly, lay out all the parts. This is a good opportunity to clean everything thoroughly.
Key Takeaway: Proper disassembly ensures you can identify worn or damaged parts and reassemble correctly.
Assembling the DR350 Front Fork Preload Adjuster
Reassembly begins with the preload adjuster. Start by fitting a new O-ring onto the adjuster nut.
Lubricate the O-ring with fork oil and screw the adjuster back into the fork cap.
Next, place a new O-ring onto the fork cap itself.
Fit the spring washer onto the bottom part of the adjuster screw and secure it with an E-clip.
With the preload adjuster reassembled, you can now move on to the fork leg itself.
Assembling the DR350 Front Fork Leg
Begin by installing the new bushings onto the fork leg. Ensure they are seated correctly.
Lubricate the damping rod spacer and slide it onto the damping rod. Then, insert the damping rod, with the spring on top, into the fork tube.
Slide the fork tube into the fork slider. Before doing so, lubricate the new bushings with fork oil. This will make the insertion much smoother.
At this stage, the bottom of the fork should look something like this:
Now, it's time to install the remaining components in the correct order: bushing, washer, oil seal, securing ring, and finally the dust seal. Referencing a service manual is highly recommended to ensure the correct sequence.
Order of Installation (Bottom to Top):
- New Bushing
- Washer
- Oil Seal
- Securing Ring (Snap Ring)
- Dust Seal
Installing the New Bushing
This step can be tricky as the bushing needs to be pressed in firmly. While a specialized tool is ideal, you can improvise using the old bushing and some tape to create a makeshift sliding hammer.
First, lubricate the new bushing and its corresponding seat on the fork slider. Slide the new bushing onto the fork tube until it reaches the slider.
Place the old bushing over the new one. Wrap tape around the fork tube to build a thick layer, ensuring the old bushing cannot slide over it. This creates your sliding hammer.
Use the fork tube as a hammer, striking the old bushing to drive the new bushing into place. The new bushing's edge should sit flush or slightly below the inner edge of the fork slider.
Ensure the bushing is pressed in sufficiently.
Installing the Oil Seal
Next, install the washer, followed by the oil seal. Pay close attention to the orientation of the oil seal. It has a single sealing lip at the top and two at the bottom. The seal should be installed with the double lips facing downwards.
Lubricate the oil seal before installation. Similar to the bushing, the oil seal needs to be pressed in. You can use the same sliding hammer technique with the old oil seal, or a suitable socket and gentle tapping with a hammer. Be cautious not to damage the seal.
The oil seal should be seated properly, flush with the fork slider.
Above the oil seal, you'll notice a groove for the securing ring (snap ring). Install this ring, ensuring it clicks securely into place.
Finally, press the dust seal into place. This usually only requires hand pressure.
Top Tip: Always lubricate seals and bushings before installation to prevent damage and ensure a smooth fit.
Reinstalling the Damping Force Adjuster
Place the copper washer onto the damping force adjuster. Screw the adjuster into the fork tube by hand. You may need to hold the damping rod to prevent it from spinning. While specialized tools exist, a piece of wood or a similar object can often suffice.
Once the adjuster is in place, torque it to the manufacturer's specification, typically between 30 to 40 Nm.
Adjusting the Front Fork Damping Force
Set the damping force to a standard setting, which is usually midway between the softest and hardest settings. This provides a good baseline.
According to the service manual, the standard setting is achieved by turning the adjuster fully clockwise to the hardest setting, then backing it off approximately 7 clicks counter-clockwise.
Finally, replace the rubber cap over the adjuster screw.
Changing the Front Fork Oil
With the internal components reassembled, it's time to fill the fork tube with fresh oil. Ensure the spring is removed and the fork tube is fully compressed into the slider.
The correct oil level is crucial for proper fork performance. Measure the air gap, which should be approximately 145mm from the top of the fork tube to the oil level. Use callipers for accurate measurement.
Once the oil is at the correct level, reinsert the fork spring. Ensure the close-pitch end of the spring is positioned at the bottom.
Compress the fork tube again and screw in the fork cap. You can torque the fork cap now or wait until the fork legs are mounted in the triple clamps, as this can sometimes be easier.
Finally, slide the fork boot back into position and secure it with zip ties at both ends. Pliers can help tighten the zip ties securely.
Your fork leg is now ready for installation into the triple clamp. If you haven't torqued the fork cap yet, do so now.
Spring Preload Adjustment
Once the fork legs are mounted in the triple clamps, you can adjust the spring preload. The standard setting is typically indicated by the third grooved line from the top of the adjuster.
Congratulations! You have successfully rebuilt your DR350's front forks. This overhaul will undoubtedly enhance your riding experience.
Frequently Asked Questions
When did the electric start DR350S come out?
The electric start DR350SE models were introduced in 1994. The DR350S, without electric start, was available earlier.
What is the correct fork oil weight for a DR350?
The recommended fork oil weight for the DR350 is typically 10W.
How often should front forks be serviced?
It's generally recommended to service front forks every 10,000-15,000 miles, or more frequently if you ride in dusty or wet conditions, or if you notice a decline in performance.
What does fork preload adjustment do?
Preload adjustment changes the initial compression of the fork spring. Increasing preload will make the suspension feel stiffer and raise the ride height slightly, while decreasing preload will soften the initial feel and lower the ride height.
Can I use a different weight fork oil?
Yes, you can experiment with different fork oil weights. A heavier weight oil (e.g., 15W) will provide more damping resistance (firmer feel), while a lighter weight oil (e.g., 5W) will offer less damping (softer feel). Always make adjustments one step at a time and test the results.
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