Vintage Dirt Bike Q & A

Many of the old manuals specified using Automatic Transmission Fluid in the forks. I'd like to get a discusion going on the pros and cons of each.

I have never used ATF myself, but as mentioned in another post I remember the Dirt Bike magazine guys used it.

I don't know all the properties of ATF, but it is a hydraulic fluid that survives under what I would think are higher pressures and temperatures than forks should produce. Maybe modern fork oils have better damping and lubricatory (Is that a word?) properties?

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

I found this valid argument against ATF on progessivesuspension.com

Most motorcycle manufacturers recommend ATF (automatic transmission fluid) for fork oil. This has excellent lubricating and cleaning qualities but we do not recommend ATF oil for one main reason. When it is manufactured it has no viscosity specification other than it must fall between 5 wgt and 17 wgt. One time you buy ATF it might be 5 wgt and the next time it could be 17 wgt. We do not feel that this is acceptable for motorcycle forks. Therefore we recommend most major brands of motorcycle fork oil. As a general recommendation 10 wgt works well for most motorcycles.

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

I have used Mobil 1 Synthetic ATF with good results. It is 7 weight and they actually list specs for it on their website complete with centistoke measures. I wouldn't be afraid to use it in any conventional forks and as an added bonus it seems to reduce stiction and give a plusher ride.

Dave Garner
San Antonio

in a 78 cr250 would you recommend a 5w or 10w?

Assuming you are not over 180 lbs and they are stock forks I would start with 5 weight oil at stock volume and height.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF