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Apparently, I should have changed my fork oil a while back............a LONG while back. I'm too embarrassed to say how long it has been, but I've got the parts on order now.

I am a huge fan of synthetic oils and I've heard about using Automatic Transmission Fluid in the front forks. What I need to know is, can I use synthetic ATF (which I have on the shelf) instead of the usual Fork oil (which is one the Dealer's shelf)?
 

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It depends. Dinosaur Dexron is about 9wt. stock spec is 10wt. Works fine.



Dino Dexron/Mercon on the other hand is too thin. Only 4-5wt.



You'll need to get the actual viscosity of the brand and type you have at hand before trying it.
 

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I just changed the fluid in my forks and used Mobile 1 synthetic ATF. It works fine. I added 3/4" spacers to the fork springs, so the ride is firmer on short street bumps at speed, but off-road, the inital

feel of the fork is stiffer, then there is no difference through the rest of the fork travel that I can tell.
 

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Thinking that my 09 TW with just 108 miles (purchased in Dec 11) had sucked up moisture during its storage, I changed the fluid. Discovered one folk had only 6 oz and the other 6 1/2 oz of perfectly appearing cranberry colored Yamaha oil. Took the opportunity to insert 3/4" poly spacers for more preload plus precisely 8 oz of Honda's 5wt fork oil in each leg. The added preload keeps the bike riding higher in the forks, while the lighter fluid really softens the forks action when in the rocks. When combined with 8 - 10 psi in the tires the suspension works 3x better for me (225 lbs) than stock. No more bottoming or jarring even when ridden aggressively. Diving under front braking is predictable and much improved as well. In addition, with the correct air pressures the bike is very civilized on the road riding single or doubled up. The combination of BS 302 3/4" preload and a lighter fork oil works well for me as so far the bike is much more sure-footed in all conditions.
 

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What do you have sitting around? Plastic, steel, or aluminum pipe or rod will work, as long as the outside diameter will fit in the fork tube. Even a couple stacks of flat washers will get the job down.
 

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I hesitate to say this due to the potential for fork seal failure and ickygooey death among the uninitiated. Fork setup is a process. But here goes:



A).If you're using the 8 oz. measurement in the manual you're getting NO fork action and ZERO rebound damping, regardless of oil viscosity. The springs are doing all the work and you're getting just enough compression damping to keep them from flailing the breeze. Cutting spacers to give more preload will only give you a warm feeling and stiffen up the spring, period. There isn't enough fluid left for the rebound orifices to do anything. Placebo effect.



. If you're using the 135mm oil height measurement listed in the manual, see above.



C). If you don't understand why this is so, use the 135mm measurement. The factory numbers are wrong, but the 135mm measurement is the least wrong and by far the safer of the two.



D). If after educating yourself on the process you are willing to increase the height incrementally by a few mm's at a time you probably won't even need a viscosity increase. Use too long a spacer and no amount of viscosity increase will fix it.



A few factoids about your TW's forks:



You have EXACTLY 6 inches of available travel. Not 6.3", 6.5", 7.0" or any of the more optimistic numbers you may read on the web. 6.00000000000000" TOTAL travel before metal hits metal.. Of this you have to "give up" a quarter of your travel for proper setup (You're not really "giving up" anything, but some folks seem to think they are).



Correct sag if kept to the bare minimum should be 20-25% of total travel. Cut spacers ONLY until you get 1 1/4"-1 1/2" laden sag under your own weight in full riding gear, no less. There is no "one size fits all" spacer length, there is only the one (or none) which applies to YOU, at YOUR weight on YOUR bike, carrying YOUR stuff.



Do the rest with oil after reading up on the concept of how air-over-oil non-cartridge forks work. No, you won't get this right in first attempt and it's entirely possible that you may not even get it right by the fifth attempt, but the results will be worth it.
 

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So, adding a little more oil will "stiffen" the forks by decreasing the amount of air in the tubes? The reason I ask is, when riding offroad with the front rack on, it tends to hit my front fender and I don't want it to crack!
 

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Few TW owners have any clue what a properly working fork feels like because they've never felt their rebound damping. These forks blow, but not to the extent they're often blamed.



The other issue is that factory fork oil level recomendations are intended as a BASELINE. It is assumed the end user is aware of that, so let's not be too quick to jump all over Yamaha. The rec's are warranty-driven and aimed at saving themselves against dinks who do stoopit stuff like filling them with 90wt.



We not only have compression damping, we also have rebound damping. But rebound damping requires that there be fluid above the orifices when the fork reaches the bottom of travel. So one reason to adjust the level is to get this feature to operate as intended. You can't get there with either of the manual's measurements as-is, but if you go too far you'll blow seals on compression. If you can't get both features to function simultaneously at your weight and with the correct laden sag, then (and only then) is it time for heavier oil.



This is a process and if you're not willing to sneak up on it incrementally you should just use the factory rec's and let it be.



IMO going lower than 10wt. completely negates any chance of seeing rebound damping at all, even without spacers.



I run longer tubes with TW internals, so my settings won't apply to anyone else's situation, and Purple weighs 110 lbs. soaking wet and needs SHORTER spacers to get enough sag. As you might imagine I've been through the process a number of times and had to do it all over again with the longer front tubes.



Here's a pic of what you're dealing with. This is your damper rod, or tube. The allen head bolt on the bottom of your forks bolts into this and keeps it centered in the lower legs. It then slides up and down inside the fork tubes, effectively dividing them into two chambers. One above the white ring, one below:







The two tiny holes in line with one another at the top are the rebound orifices. They're smaller to slow the return of fluid because the spring forces are greater in rebound.





The staggered, much larger holes at the bottom are the compression orifices. There are 2 more on the other side, total of 4.



Thicker oil slows down BOTH compression and rebound in a more or less linear fashion. Sometimes this is a good thing, but only up to a point. Thicker oil has a downside in that after a given viscosity it won't flow through the smaller orifices in time to replenish the compression side and it will reach a point where it just sits in hydraulic limbo unable to make a decision, indefinitely.



In general the best approach is to use the thinnest oil possible to get the job done. Yamaha's fork supplier sized the orifices around 10wt. oil flow characteristics so your first and best course of action is to try to get the thing to work with 10wt. oil. Learn the ziptie drill and see it through.



(Note the corrosion on this tube. This came from a bike that had been sitting for a couple of years. The tubes were rusted and the compression holes were completely clogged with sediment. This is why it's never a bad idea to completely dissassemble the forks on an old bike. At minimum a thourough flush is in order unless you knowfor a fact that the bike was maintained meticulously. This bike had plenty of fork oil, but it was contaminated by moisture. That's why fork oil needs to be changed regularly, even though in theory it never breaks down from heat like the oil in a crankcase. In essence it is always raining inside your fork tubes.)



Anyway, under compression the fluid gets forced from the lower legs, through the lower holes into the upper fork tube. In rebound it gets sucked back through the two tiny rebound holes and returns to the lower legs. If there's nothing above it but air you get no rebound action.



The fork will also bottom easily because the air gap is too great.



You need to get these two items balanced. So you see the solution has more to do with oil volume than viscosity.



While our forks are incredibly simple devices the concept of their operation can be difficult to grasp until the light comes on in your head, so don't feel dopey if that applies to you. I recomend you cruise the 'net and read as many explanations as you can until you grasp the concept. They really are inanely simple, but we all learn differently so read all you can til someone's explanation sticks. Some people may need to take one apart before the light goes on. Don't matter how you get there as long as you do.



Somewhat of an oversimplification, but essentially all that cartridge-type forks and emulators do is allow you to vary the size of the orifices at will. Our forks have fixed orifices, but MOST of the same changes can be made through a combination of air gaps, spring preload and viscosity.



If all of this seems like a PITA, it is. This should also help to explain why some of us dislike the later models, or more to the point, what Yamaha did to cut corners on the later models. The absence of fork drains is no longer a minor inconvenience, is it? Their absence discourages both routine maintenence and proper setup in one swell foop.
 

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Good essay on the forks, lizedbrth. actually, the size and shape of the dampning passages can be modified to change the compression/rebound dampning ratio. this was common back in the days when typical forks and shocks had next to no rebound dampming and a relatively powerful compression dampning. Lots of trial and error (welding and drilling) to work out the best feel. Spring-loaded ball valves were added to allow a soft ride on little bumps and more dampning on hard hits. Washboars were fun if you got the ratio too far out of whack--the shocks/forks would either pump up to full extension or down to bottom out, resulting in wierd rake and trail and sometimes a quite jarring ride.
 

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Factory fork oil amounts in my 09 TW were 6 oz and 6.5 oz. Based on first hand experience that factory installed (KTM!) fork fluid amounts could be too much or essentially none at all, I used the 8 oz spec'd in the manual. After testing and the discussions above, I would agree that 8 oz is too much.



1. Is there a thread detailing the referenced "ziptie drill"?



2. Agreeing that 135mm measurement is a more "appropriate" starting point, what does the 135 mm equate to in ounces?
 

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Buddy, 8 oz. is too little, and 135mm is slightly more but still too little and that's my point. Anyway here's the basic procedure for setting the oil height for your body weight. This is not for everyone. It requires considerable time and effort. As I said earlier, unless you wamnt to go there as a process you're gunnado more harm than good.



Ok, first of all we're gunna assume that we're using 10wt fork oil. You can use any weight you want to, but the only way you'll know if you're pizzing in the wind is probably to begin with 10wt.



First, set your oil level at 135mm. Mostly because we need a baseline. Remember that the oil levvel is measured WITH THE SPRINGS AND SPACERS REMOVED AND THE FORKS FULLY COMPRESSED.



Put your springs and spacers back in, then (very important) put your fork caps on with the FRONT END LIFTED FULLY OFF THE GROUND! Be sure to do this after each and every oil level change. If the forks are compressed even slightly when you put the caps on you'll change the air gap and all your effort will be wasted.



The "ziptie drill", grossly over simplified:



Jack bike up so there's no weight on the front wheel. Zip a ziptie around the fork leg below the lower triple tree. Slide it down the leg til it rests on the fork seal. I usually remove the boot from one leg because this takes awhile to accomplish and the ziptie is easier to see without it. Leave the ziptie on til your fork is completely set up, even if it takes a month...



Stand the bike up under its own weight. The forks should drop slightly. That's your static sag. Not super important right now, but there may be as much as 1/2".



Now get someone to hold the back of the bike vertical while you put both feet on the pegs and your hands on the grips. The front end should drop further. The ziptie will slide up the leg and mark the travel. You can do this solo if you park next to a wall and slowly push yourself vertical with one hand on the wall. You want to do this in a controlled manner so you don't get a false measurement. Do it a few times to verify the measurement.



Lift the front end off the ground. The difference in the measurement between the bottom of the ziptie and the fork seal is your laden sag.



We have 6" of available travel. Most street riders allow 30% of total travel for sag. 20% is bare minimum, 25 is generally accepted as resonable for offroad and dualsport bikes.



In inches that means you want somewhere between 1 1/4" and 1 1/2" LADEN sag when you park yourself on the bike. Here's where your spacers come in. You want either longer or shorter spacers, whichever gets you to the proper sag with the stock spring rate. Keep in mind that every milimeter of spacer you add increases the compressed spring rate which will force you to use heavier oil to compensate. Keep the sag around 25%



No magic bullet here. Get some PVC tubing and cut spacers of various lengths till you get it right. I never said this would be a picnic, no?



Ok, so we got our spacers set to deliver the proper sag.



A word about spacers. I prefer to cut metal spacers once I have the length right. A lot of people aren't messed up about leaving PVC in there permanently. Whichever you do, use PVC initially until you get the length worked out. Particularly if you need SHORTER spacers, as some really lightweight folks may need. You don't want to ruin your stock spacers by cutting them until you've got the exact length figured out in PVC.
 

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Ok, now we're gunna go for a ride in the dirt with our friendly ziptie on the fork leg.



If you never ride offroad you get off a bit easier, more on that later.



Wring the bike's neck fairly well, unless you're already bottoming constantly. If so, skip a step.



Now look at your ziptie. Lift the bike and measure. I'll almost bet you'll see a full 6". No bueno. If you're only using 5-5 1/2" and you're riding the bike hard enough you may be in the ballpark if you weigh under 125 pounds or so.



Now we're gunna do the whole oil level drill again. We're only going to increase it by 5mm to 130mm, put it back together, and ride. (At some point during these gradual incremental changes you should begin to feel your fork "working". Don't be skeert. You'll get used to it
.) The first thing that will happen is that they'll start to feel firmer. That's the first sign that you're almost there. Don't overdo it or skip a step and add 10mm of oil, sneak up on it in 5mm increments, max.



Our goal is to use as much travel as possible without bottoming, with enough air gap that we don't blow out fork seals yet enough oil in the forks to allow the rebound to work properly. To do this you really have to sneak up on it slowly. The ziptie is gunna tell us when we're there.



At some point you're going to get more fork action in the form of compression resistence, and you'll start to hear the second "hiss" as your forks rebound. Your ziptie will begin to use less travel over the same riding course and this is where things start to get really critical in terms of oil level vs. firmness, particularly if you're a heavy rider.



Let's say you're no longer bottoming constantly on the big hits and your ziptie consistently stops in the 5 1/2" to 5 3/4" range. At this point your fork is "working" properly in both directions. It may be or may not be overly stiff. Here's where you need to make some decisions and/or compromises. This is also where opinions will vary greatly, and I'm sure there will be some discussion on the finer points.



You can stop here. If you like the feel of the fork action you can call it good, record your height measurement and use it forever. If it's too stiff you can back off some fluid, til it feels right, tolerate some bottoming on the really hard hits, record the measurement and use it forever.



If you're a heavyweight you may have added a lot more oil to get here. You'll have to judge this for yourself, but IMO if you're getting into the 100-110mm range for fluid height you're possibly going to increase the chances of blowing seals. This is the point where you weigh things out and consider heavier oil, but you'll need to repeat the drill again.



Conversely if you're a lightweight you may find the fork too stiff and you may be able to switch to a lighter oil.
 

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Listen to the Man. Lizdbrth knows where the TW gold is buried. Listen to the MAN!



1. Get the front SAG correct, then

2. Make sure the fluid level is set at the correct height using the standard methods to measure the oil height,

3. and then maybe consider using a different fork oil weight.



ONE is worth 50%, TWO is at least 40%, and THREE might be worth 10%. Don't make it more complicated than necessary,



I've been riding for years, and setting the front SAG just doesn't come up in the conversation very often. Lizdbrth is the first guy to adequately explain setting front SAG to me and does so in the context of the rest of the front end setup.



if you follow his advice and guidance you'll maximize the potential of your TW without spending a bunch of money or chasing some phantom solution that you'll never be able to find and if you do, won't be able to afford.
 

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Once again, many THANKS Russ... I think we should have Wes lock this up.. If we keep it easy to find, those willing to spend just a few minutes looking will have a great step-by-step tutorial. Appreciate all the work you do in making this a great forum. Gerry
 

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Good tutorial, lizrdbrth. Same tuning philospohy as a carb--one small step at a time and test, letting the bike tell you what needs to be done.
 

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Once again, many THANKS Russ... I think we should have Wes lock this up.. If we keep it easy to find, those willing to spend just a few minutes looking will have a great step-by-step tutorial. Appreciate all the work you do in making this a great forum. Gerry
Having this "locked" or "pinned" is a great idea. As a new member I don't have a lot of luck in a search-and that is using the method recently described. I think part of it is knowing what the part/idea was called in the thread. For my other bike, over at Adventure Rider there is a F800 links and resources which stacks and categorizes the information into easily searched threads. If that was possible here, I think it would help. OM
 
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