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how often should you replace fork fluid

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i just bought a used 07 yz250f with less than 8 hours on it and was wondering if i should replace the fork fluid, if not how many hours before you should, and should i tear it down and grease all the bearings

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I'm no suspension expert, nor am I a fluids expert however i've made some observations and read a lot about both subjects:

My observation is that most riders don't replace it until their seals go. Amateur racers who know the value of their suspension get it done with their service and re-valves, but often let it go until there's a problem. The truth is, it's a big hassle to tear down the bike, take the forks apart and replace the fluid. The shock is even more of an issue as most guys don't have a nitrogen tank and regulator to re-charge the reservior.

The fluid gets contaminated by the material that wears off the bushings and other parts inside the fork, plus any micro-dust that gets by the seals, etc. Also, the molecules in the oil will break down over time just like motor oil or gear oil. So the suspension slowly changes and becomes less consistent as time goes on.

In reality the fork fluid should be changed at a minimum of once per season.

I try to do it every 4 months of consistant riding along with my brake fluild.

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i just do it every season. my manual recomends every 10 hours but i don have that much time. i can't notice a difference when a change the oil. tear the bike down? it only takes 10 mins to change oil. unless you want to take apart the fork fully and flush every thing

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I can feel the fork fluid starting to wear at about 15 hours of hard mx. Suspension tuners recommend fork oil be changed around 20 hours for maximum performance. But unless your a sensitive rider, or pretty serious racer, once a season is usually plenty fine.

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I can feel the fork fluid starting to wear at about 15 hours of hard mx. Suspension tuners recommend fork oil be changed around 20 hours for maximum performance. But unless your a sensitive rider, or pretty serious racer, once a season is usually plenty fine.

Agreed.

It's just like motor oil. It heats up, gets shoved around breaking it down further. You pour in 5wt and it pours out with less viscosity.

I have around 40 hours on my current fluid (way to long) and I can tell a major difference. But tomorrow's the last race of my season then it's time to tear it all down.

I'm going to give Dave's fluid a try with one of his kits.

I've heard claims of over 100 hours with this fluid.

My suggestion, change it when you notice a difference, or every year.

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Intensem1rider and GMO397, I agree with you guys 100%... you have to be a sensitive rider and know your setup to feel such a gradual change.

The best way to feel and understand the difference is to go ride your bike with old overused fluid, put in a few hot laps and get the suspension warmed up. Change the fluid and re-assemble everything. Then go out for a few more laps. You'll feel a distinct difference if your fluid was really beyond it's useful life.

Some riders can feel a single click on compression or rebound... with others, you cand spin the clickers 5 clicks or more and they won't notice a thing.

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I'm one of the evil guys that just change when they do seals. I think it's a good idea to also grease the bearings if you just bought the bike. I don't necessarily have a service interval for greasing bearings, I just do it more often if I've been doing a lot of water crossings or mud riding.

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yeah i just tore tore the front end apart and greased the steering and front wheel bearings, the stock greases was like new, no dirt, no rust, i just put in my stuff maxima and reassembled, judging on the bike im not going to change it, the paint is not even wore off the clutch cover at all, cant believe i found this bike payed 2600 for it, the guy bought it 2 months before he went to iraq....... so im going to wait on the fork fluid causes changing it now i think is a waist of my money, im 15 so i cant just through away 40 bucks changing it when the fluid is probably like new ya know

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I just change it every time I swap my seals out. And since it is a Yamaha, that works out to around every 5 hours of riding time....LOL

lol yeah got that right, i know if you use msr or all balls fork seals they leak after little use, have to go with stock or something like stock, my buddy replaced his with tusk fork seals from rockey moutain which are the same as stock an there still not leaking

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I just change it every time I swap my seals out. And since it is a Yamaha, that works out to around every 5 hours of riding time....LOL

How do you manage to only have them last 5 hours? Do you have knicked fork tubes or something? I've never had a leaking seal and I've only ever changed the seals on my YZ cause I figured nobody had done it since it was brand new.

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How do you manage to only have them last 5 hours? Do you have knicked fork tubes or something? I've never had a leaking seal and I've only ever changed the seals on my YZ cause I figured nobody had done it since it was brand new.

I think he's being a tad bit sarcastic, mister serious.

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I think he's being a tad bit sarcastic, mister serious.

Even still, if it's a repeat failure I would look more towards installation method or a problem with the fork tubes themselves.

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Even still, if it's a repeat failure I would look more towards installation method or a problem with the fork tubes themselves.

Yes, I was being a tad sarcastic. So... between myself and my riding two riding friends we have 4 Yamaha products. I have a WR450, an almost new 05 YZ250, and friends have a WR450 and 250. My WR had the forks done by a local suspension shop and literally less than 10 hours in both seals were not just seeping, but LEAKING. Tried the old fork seal cleanout I did, no better. So not being a newbie to forks (which I'm not) I pulled them apart, checked the seals, couldn't see anything wrong with them, and installed new seals. All bushings were checked, all tube surfaces were checked, and we were all good to go.

Three fork seal jobs later, all averaging about 15-20 hours before leaking, here we are today. Now granted, after the first one I don't change the seals right when they start leaking just because... well, the sooner I change them, the sooner the next set will fail. Oh and before you say it, yes I've tried all different sorts of brands, and no different result.

Fast forward to the YZ... Long story short, previous owner put $1200 into the suspension to have it set up for woods racing from a very, very well known shop in the north DFW area. They are truly a thing of beauty in the woods, I promise you. Well... about 10 hours into me riding it, guess what... leaky fork seal time... Also before you say it, I despise riding in the mud and/or sand and avoid it if I can. It ruins parts and I'm cheap, so what can I say.

Friends... Their WR's have both had three different seal jobs that I know of by 2 different shops and then we did the last one because they were tired of paying a shop to change fork seals that often.

Any Honda or Suzuki forks I've ever changed out never leaked on me after servicing. I haven't ever messed with Kawi suspension, but man Yamaha sure does design a leak prone fork.

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On my race bike I "service" my suspension half way through and at the end of every season. I agree... I can start to feel a difference at around 20 hrs. which is about half a season since I only ride it durring races and a few practices to dial in suspension and stuff most of the time.

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Don't the newer YZ have some special less resistance seals? I think read it somewhere that they do. Less friction should translate in more leaking. I am trying seal safers and it works for me.

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