Fork Fluid Question

43 replies to this topic
  • Ga426owner

Posted August 29, 2001 - 02:13 AM


I have seen numerous post on using Mobil 1 ATF as Fork oil. What have been the results from you all that use this? Also for those that use Yam 01, Belray or Silkolene. What about 5w vs. 7w? Is airtemp the factor here?
Any advice is appreciated. Thanks

  • SUnruh

Posted August 29, 2001 - 03:22 AM


you should talk to these people:

Jeremy Wilkey at MX-Tech
Rob Mann at GP-Racing
Jeff Howe at TrakControl Dynamics

all 3 are very well known for their suspension work. all 3 of them use Mobil 1 ATF in some if not all of thier suspensions setups.

  • Ga426owner

Posted August 29, 2001 - 03:41 AM


SunRuh, how does the ATF stand up? How often does it need to be changed?

  • SUnruh

Posted August 29, 2001 - 04:58 AM


i have no complaints.
i will run a full season of harescramble racing on it before i change it. same goes for the shock.
the one thing about Mobil 1 ATF is that it is thicker (10wt i think) and each turn of the clicker gives you MORE change than a lighter fluid does.
you have to realize up front that ATF is designed for 25,000 miles in an automatic transmission. it is MADE for long term use and extreme heat. your forks and shock will not come close to that kind of environment and therefore it really, really lasts.

  • Roostie_1

Posted August 29, 2001 - 08:24 AM


Is the Mobil 1 ATF a Dextron III rating? Just curious.

  • sirthumpalot

Posted August 29, 2001 - 10:03 AM


How are you changing the oil in the shock? Are you having it done at a suspension shop?

  • DaveJ

Posted August 29, 2001 - 12:20 PM


I still think it may be worthy to investigate why these suspension shops are finding better results, other than profit, with the use of ATF.

There would seem to be a lot of design considerations into forks and shocks based on fluid dynamics, that of O1 fluid. Modify the oil, and it would seem that you would have to modify the component to match.

In addition to this, there has to be a reason why Showa, KYB and Ohlins use the 01 fluid, as do most factory teams.

I'm not saying not to use ATF, I would just like to see a more technical argument made, especially when considering the variables in settings for trail vs. SuperCross configurations.



  • sirthumpalot

Posted August 29, 2001 - 01:01 PM


DaveJ I agree with you. As an engineer I tend to question everything which doesn't match exactly with what is recommended by the designers. After all, they should know best.

Just one more thing to add to your list. I have no proof, but I would suspect that suspension oil would be more consistent viscosity wise than something like ATF which doesn't need to be as precise. Could the average person tell the difference bottle to bottle? I have no idea, but I'll let someone else test it and give me the results. :)

  • DaveJ

Posted August 29, 2001 - 02:26 PM


Sir Thump,

Thanks for the addition.

This may sound a little sick, but just to be safe I usually blend multiple bottles of the same fork oil before I refill a set of forks. This assures a perfect visc. match between the legs.


  • SUnruh

Posted August 29, 2001 - 03:21 PM


typical 01 fluid has a VI of around 400. M1 ATF is around 198. jeff is currently working on some new blend of semi-sythetic that would flow well, but not cost as much as 01.

i have M1 ATF in my bike and like the way it rides. i race harescambles and plushness is a must.

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  • Dave_S

Posted August 29, 2001 - 08:11 PM



Have your forks been revalved? I tried Mobil 1 in my stock 00 forks and found them too harsh for a rough MX track. Went back to 01 and was much happier.

Dave S

  • SUnruh

Posted August 30, 2001 - 02:59 AM


dave s,
yes, it was re-valved for woods racing before i even took possession of the bike.

  • Ga426owner

Posted August 30, 2001 - 03:10 AM


So, what is the consensus for ATF in a motocross/supercross set of forks? I am in the process of completely rebuilding my YZF forks this week. I am revalving, checking mid-valve, replacing seals etc... I have .47's already. Last weekend at local Moto - I suffered complete fork failure...With 3 clicks out on the compression -- forks bottomed so harsh that you heard clank on every landing -- braking & acceleration bumps were brutal. They got worse as the day went on. Pictures on WR discussion tell the deal as the forks bottomed so hard my brains rattled. I am attempting fixes with my Tuner. If I am not satisfied, it's off to Enzo or MXTech.

  • sirthumpalot

Posted August 30, 2001 - 04:57 AM


My personal opinion is that you can not go wrong with the fluid which was designed for the forks.

  • Scott_F

Posted August 30, 2001 - 07:57 AM


If SUnruh is correct, then the Viscosity Index would be adequate for forks, if it provides the desired viscosity. If I had a Honda, I would definitely use it in the outer chamber. I wouldn't use it in shocks due to the low VI.

Steve, I wouldn't run any fork oil for a whole season. It is better to change it regularly due to how dirty it gets from fork wear. If left in, the aluminum particles in the oil act as an abrasive slurry, further accelerating wear. Since the ATF is relatively cheap, it would be worthwhile to flush the forks with new oil every 5-10 hours riding.

DaveJ, on the oil mixing, I wouldn't call it "sick", just meticulous. :)

Ga, you may indeed have a blown midvalve. While you have Tuner replace it, you might consider bottoming cones.

  • Ga426owner1

Posted August 30, 2001 - 08:07 AM


Scott F you commented on the WR side about the jump & my landing on the Step up. Do you or anyone else think bottoming cones are the ticket or worth the $???????

  • Ga426owner1

Posted August 30, 2001 - 08:09 AM


Another quest: Scott F or anyone else. If the midvalve is blown, is it better to replace it with Yamaha or does anyone else have a better solution?????

  • DaveJ

Posted August 30, 2001 - 09:09 PM



Unless you're using your bike just to fetch firewood, I would highly recommend bottoming cones. Consider them as a health related issue. ScottF can chime in on some further details as he seems to be a man of big air.

As for mid-valves, the only way to replace it via Yamaha is a complete compression tube. About $275 per tube if...umm....memory serves me correctly.

It's best to pull it and run a restrictor plate, or just rebuild it. Some of the suspension shops have their own way of dealing with this thing. See previous posts for further details.

As for its usage, I'm slowing learning why Yamaha put it in.

For those that have yet to learn this lesson, a soft suspension is not a fast on. This is the concept behind the "plush-but-firm" approach that many top tuners speak of.

Soft causes the mass of the bike to sink and ride deeply into every hole in encounters (with you included).

Firm causes the bike to skip or ride high over the bumps and holes. A rather fast approach getting from point A to B, not to mention it doesn’t beat the rider up as much.

The trick is to make sure you have enough suspension to stick, without skipping.

So back to the mid-valve.

SuperCross tracks are very unique in that they don't have little bumps. They have big jumps and whoops, and the filler is relatively smooth. In this case, at extreme speeds, I can see the application of the mid-valve, but not without some tuning to the track in which you're riding.

Sometime ago I had posted some stuff on fork nirvana. Still true, but with some additional testing at some more aggressive tracks, I have once again learned the importance of application specific.

Clearly the level of plush-ness that works best on the trails does not apply to the big tracks.


  • DaveJ

Posted August 30, 2001 - 09:20 PM


By the way, I'm beginning to become a little suspicious as to what is causing the mid-valve to "wear-out".

I possibly could argue that the mid-valve itself is not the problem, but that it's just extremely sensitive to the quality-state of the oil. As is the seal head assembly. Mainly that when I have lost sizable amounts of compression, that fresh fork oil seemed to resolve it.

I've done the flip-the-shims approach as well, but never without new oil.

This has also contributed to my bias towards the longevity of certain lower grade oils.

Any additions to this theory would be helpful.


Okay – I’ll shut up now.

  • Ga426owner1

Posted August 30, 2001 - 09:20 PM


DaveJ, thanks for the feedback. Suspension Science is Chinese to me. You have a way of explaining things very clear to me regarding this post & your past "nirvana" post. Is there a way to strengthen or beef up the midvalve w/o affecting oil flow performance in a negative manner? Would a "strengthen plate" work ie..larger or thicker shim? Also, who do you recommend for bottoming cones?

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