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FORK OIL vs ATF


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It has been the recommended oil in many damping rod forks for decades. If I remember it is about equivalent to 10wt motor oil with huge amounts of cleaning agents and defoaming additives. You can find the info in the oilfaqs on the interweb. (Use Dexron and not Type F, Type F has friction modifiers for the clutches and can cause wear. So I'm told.)

YMMV JOIMO.

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It has been the recommended oil in many damping rod forks for decades. If I remember it is about equivalent to 10wt motor oil with huge amounts of cleaning agents and defoaming additives. You can find the info in the oilfaqs on the interweb. (Use Dexron and not Type F, Type F has friction modifiers for the clutches and can cause wear. So I'm told.)

YMMV JOIMO.

I don't use ATF anymore but used to and if you rub your fingers with a bit of Dexron III it feels kind of grippy. I don't think that's the best ATF for forks. I ended up using Fuchs Titan 95LE which is friction modified and seems a lot slipperier. I was told to use it in my Honda US Wagons gearbox because the box used to thump into gear using Dexron and it smoothed it right out. I tried it in open chamber forks and was very happy with its performance but it is heavier than 5wt so suitable for some applications, perhaps not so suitable for others.

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Tried and true for damper rod forks. One issue is the viscosity rating of oil is at 100 degees C, and all oils thicken as they cool, the amount of thickening is determined by the base stock and additives. As a result different brands of 10wt (or 7wt) will have different viscosities at 70 degrees F. The base stocks with the least thickening will be the synthetics, so I recommend using the synthetic and stick with one brand for repeatable results between oil changes.

Don't know if you can get ATF in a thin enough grade for cartridge forks, a friend tried ATF in his cartridge forks and didn't like the harness on sharp edged bumps.

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They dont rate them as weights. Just the TYPE of ATF. That is the problem with the ATF, there is no specific "weight" associated to it.

Just dig into the product data sheets of the ATF , fork oil or whatever you want to compare. Look at the viscosity at 40c spec. Hint, weight is a range not a specific, so 1 brand 5w might be thicker or thinner than another brand. That's why it's good to know the 40c of the product your using and the product your changing to, so that your going the direction you want.

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If you really want to be economical about it. Find a synthetic

Amsoil hydraulic fluid. AW 15,22,32. AW 22 might be the sweet spot

as far as viscosity and performance goes. AW is cheaper by the

5 gal. Look online, you will be able to find it for 130 bucks, plus shipping

20 bucks. At 150 bucks you have a 5 gal bucket of fluid to run

in your forks and shock. The viscosity is around 6 cst @ 40 c

and around 20-22 @ 100 c. VI is 256. Dont the exact number, just going

from memory here. The down side of this is if you dont like the

fluid, you have a 5 gal bucket of hrydo fluid laying around.

Hope this helps:thumbsup:

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I have used Moble 1 ATF when I am testing different shim stacks on my forks. It is said to be around 7.5 Wt. Alot cheaper than fork oil when you know you will be tearing the forks down several times during testing.

I always switch back to good quality fork oil on my final setup.

I find that the ATF is very temperture sensitive and gives inconsistant results. From a 90 degree day to a 50 degree day they just feel different. My guess is that forks just won't get the fluid hot enough to get to its operating temperture to be more consistant.

It doesn't cost much to try it. May work good in your forks.

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just got back from test ride... maybe 150 miles, but gps is broke again... no leaks at all... i used mobil one syn atf... i could hear a little bit of "squish"? when compressing the legs off the bike... not sure if that is normal... bled forks off bike, but still the same...

everything definitely feels a little different, but i'm still riding fast enough to miss some turns, so it seems adequate... i also have sweet almost new front tire and a bald ass back tire... suspension feels incredible hitting rocks, ruts, whoops, flat landings etc straight on, but everything reacts really fast when i start turning, especially on outer knobs... thought it could be tire pressure, but guage was broken, felt like it had air, but might have been soft... seems adequate for now...

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There's even some OEM Manuals that recommend ATF as an alternative. I can't remember exactly which bikes these manuals where related too, but if you're interested, I'll figure it out.

1995 and older cr250`s are a few. They suggest ATF in the shocks too.

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  • 10 years later...

anytime your trying to replace a product with something else your going to get a lot of experts chiming in , your going to just read up on it but a fork is just a hydraulic tube so get a lubricant that doesn’t have silica or a detergent and you will be fine, I have some owners manuals that even say to use ATF If no fork oil is available, just research it.

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I bought a used 07 CRF450R recently and my first task was to change all the fluids throughout of course. Crankcase,trans, and radiator were day 1. After about 10 hours of riding it i dove into the suspension front and rear. Both felt horrible but neither leaked. The screw adjusters were at the factory settings. I discovered that the forks were refilled with red ATF as were the dampers. Im 210lbs so i replaced with 7w Bel-ray fork oil, and replaced seals and bushings. They feel good as new now.
In the rear shock i found an unidentifiably dirty substance that was about 5% foam and the nitro can was down to 85psi. I replaced with Bel-ray 3w along with new rebuild kit, refilled nitro to 142psi and the bike feels fantastic.
The purpose of this story is to make u ask yourself if a few dollars is worth experimenting with one of the most critical components of your machine.
IMO, it is not.

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On 5/12/2019 at 1:21 PM, Slip Angle said:

I bought a used 07 CRF450R recently and my first task was to change all the fluids throughout of course. Crankcase,trans, and radiator were day 1. After about 10 hours of riding it i dove into the suspension front and rear. Both felt horrible but neither leaked. The screw adjusters were at the factory settings. I discovered that the forks were refilled with red ATF as were the dampers. Im 210lbs so i replaced with 7w Bel-ray fork oil, and replaced seals and bushings. They feel good as new now.
In the rear shock i found an unidentifiably dirty substance that was about 5% foam and the nitro can was down to 85psi. I replaced with Bel-ray 3w along with new rebuild kit, refilled nitro to 142psi and the bike feels fantastic.
The purpose of this story is to make u ask yourself if a few dollars is worth experimenting with one of the most critical components of your machine.
IMO, it is not.

You could just as easily attribute the improved fork action to replacing worn fork bushings.  Slightly thicker oil will only affect the bleed circuits.  Once the shim stacks open your damping is not significantly affected by minor differences in viscosity.

I don't run ATF in forks, it is not designed to be slippery.  I use 0w20 motor oil with great results.  It doesn't have the viscosity index of fork oils but I have no issues running it year round, and I am certain it does a better job at lubrication.  It always comes out looking great.

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