This maintenance task is probably the most difficult of all of the owner's manual routine maintenance tasks. It is supposed to be done every 50K miles. I don't know how I feel about waiting that long. That just seems to be a lot of miles on the bike before changing the oil out of the forks. However, if we stay true to Harley's specifications, you should be good at riding it up to 50K miles. I performed this fork oil change and made this video at 41K.
Service Manual Interpretation
I want to stress that this video is specifically for a 2012 Street Glide. The year of your bike and the model could change the process slightly to extreme. Some bikes have conventional forks; some have damper valves, some have a conventional on the left side and a damper on the right. You will absolutely need a service manual for your specific bike if you're going to perform this task yourself. Another point to be made here is that the service manual specifically states that the forks must be removed to change the fork oil on a Street Glide. That is not completely accurate. Once removed, the Fork Cap Bolt opens up the top of the fork, providing access to fill without removal. There are also screws with a copper washer at the bottom for draining the oil. Between these two specific factors, you are provided with a means of draining and filling without removing the forks. However, this is ONLY good for changing the oil. You will have no way of checking internal fork components for wear or breakage doing this. I think that the service manual says to remove the forks, springs, and dampers to provide the chance for a visual inspection of some of the core components. I believe Harley says to remove them to be more thorough in checking for possible wear from a safety perspective, which I can understand.
Knowing The Feel Of The Forks
I've been riding bikes for over 40 years. You get to know the bike's feel and how it handles under different road and temperature conditions. When a problem occurs in the front end of your bike, it doesn't take long to notice that it's not handling right. If a seal pops and oil starts flowing out, you'll know. If a spring snaps in a fork, you'll know. Even if the fork oil is breaking down from over extended use, you'll know how the bike handles. So if the bike is handling right, then at least at that moment in time, you can be reasonably sure that nothing is broken, and performing just the oil change will be fine.
Clean Oil Extends The Life Of The Forks
If you keep up with this, then the clean oil you keep in the forks will help to extend the life of the internal components. Dark oil, either dark brown or black, is a sign of wear. It is dark because internal parts break down and leave a residual that turns the oil dark. As the oil breaks down it fails to protect the parts well which causes the parts to break down more rapidly. So if you keep the oil clean with regular drains and refills, the components will last longer. Fork oil gets pushed through a bunch of small holes and valves to provide dampening; the friction of the oil moving makes it quite hot. This heat will break down the oil and cause a viscosity change, causing your bike's forks to work less efficiently for suspension and braking. All of that to say, there is good reason to drain and refill your fork oil without necessarily removing the forks.
Tools For The Task
You will need three specific tools for this, which most people just don't have. A bike jack, a #3 Phillips screwdriver, and a 1-⅜" wrench. You'll need the jack to keep the bike upright and get the front wheel off the ground to fully extend and decompress the forks. This will help with the refill procedure. A large wrench is necessary to get the fork cap bolts off. There isn't enough room for a large crescent wrench to be able to turn the bolt enough and get it loose. There's also not enough room between the fork cap bolt and the handlebars to fit a large socket. So you're stuck having to use a box-end wrench to remove the fork cap bolt. The #3 Phillips screwdriver is for the drain screws. Anything smaller, and I just don't think you'll succeed in breaking them loose without rounding them out.
Type Of Fork Oil
I used the Screaming Eagle Heavy Fork Oil, which is heavier than the Type-E oil the bike comes with. This will provide for a stiffer ride and allow for better handling. If you want a smoother ride but a squishier front end, then stick with the Type-E oil. If you're into competition riding, the heavier oil would be perfect since the bike would be more responsive and handle better. Some people that ride part-time or maybe cruise freeways without a lot of turns might like the smoother and softer ride of lighter oil. You'll have to decide for yourself because it really is a matter of preference.
Watch the entire video to get an idea of the process before trying. This maintenance task may not be something you even want to attempt. Also, keep in mind that getting the correct amount of oil in the forks according to your service manual is necessary. Too little could cause handling issues which could lead to a crash. I hope the video provides a thorough process overview for you to decide whether to do this maintenance task or not.