Ever wonder about fork oil?

When I started getting serious about maintaining and tweaking cycles long ago. I ask a guy I worked with which fork oil brand he prefered. He is a top tier flat track/ ice racer and has rebuilt more forks than I have looked at. His answer? Silcolene, why? Be cause when he rebiulds them Silcolene has always been cleaner hence the least amount of wear.

when rebuilding rear shock it is Important to get ALL of the air out of the shock oil - air in oil will cause it to foam -not good-

after filling shock let sit for a hour or so to let air bubbles rise and escape
(move shock around and work thru stroke )

pro shops will put a vacuum on shock after rebuild to remove air bubbles-
makes a big difference -

Used to use ATF in my MTB forks. Some caused seal swelling ( I think) and the seals would weep.

Agree with the other posts about the PITA marketing driven fork oil "weights". It seems to be pretty much trial and error, find something that works and stick with it. I too like the Silkolene 5 weight in my 'Berg's WP open cartridge forks.

Although some bikes spec it (usually damper rod type forks) ATF may not be a great idea - talked to Alan Stillwell about that, he said it is a "dry" oil and that the bushings tend to wear faster.

That's ridiculous

Folks won't take you seriously if you just post a dis. If you have some argument, preferably by someone well-known, then post it so we can be edjumacated.

BTW, here's Stillwell's credentials: http://www.stillwellperformance.com/

I'm guessing here but I bet "dry" oil means it doesn't have much film strength (stickiness), perhaps because its not needed in a tranny; obviously some have found its needed in forks. More importantly, forks need suspension fluids with stable hydraulic properties (over a wide temp range as the forks heat up), and ATF is just not designed to perform as a hydraulic fluid.

Then why are there so many happy "ATF as a suspension fluid" customers out there? Lots of common misunderstandings out there - like folks using WD-40 as a lubricant... its not, its for "Water-Dispersing" (formula #40 of their R&D process) - but practically speaking, some folks use ATF in suspensions, don't notice any problem, and then assume there are none.

Hell, I use Windex to clean just about everything in the house, and I'm pretty sure its not optimal

Bump bump.

I'm still looking for the answer to this question as well. Can't seem to find the tech specs for BMW fork oil (OEM p/n 83192182459) anywhere. As I start my adventure into playing with the forks on my old thumping F650 I'd like to know what my baseline is and what BMW actually throws in there. Anyone know any viscosity stats for the bmw fluid? cst@40? cst@100? Viscocity index? Anything to use as a starting point other than "buy the BMW candy?"

thx

cant go wrong with fork fluid for cartridge forks..
http://www.maximausa.com/product/racing-fork-fluid/

Well many people probably do it because the manuals for old bikes called for it. My manual for my 1980 suzuki says ATF specifically for fork rebuilds.

Someone should tell "Lucas Oil" that (according to a internet forum) ATF and Hydraulic Fluids are different

I can't quite tell which camp your jibe is directed at. Either way, for the applications that product is designed for (tractors) the transmission fluids also act as hydraulic power transmitters the same way ATF's do.

Traditional ATF's also have hydraulic properties in terms of fluid stability and wear protection. However, ATF is also meant to provide a certain level of friction to operate specific transmission designs. Fork oil is designed to provide the lowest amount of friction to reduce static friction and wear, and improve damping consistency.[/QUOTE]

Not directed towards any camp... just like to poke the bear when I can't

They don't seem to want to publish it - even if they claim its "superior"
https://www.ascycles.com/Oil-BMW-Fork-Oil-10w-1000ml-31429062158

Use anything with a known value. Ignore the BMW stuff since if it is unknown, it's not helpful to you. But yes that does mean you are starting from scratch, one step behind. You'll soon catch up.

There has certainly been lots of back and forth in this thread.

The bottom line for me is that fork oil is basically just a hydraulic fluid and this works just fine in my KLR.

What are your trying to achieve by using ATF rather than the more specific fork oil?

At my local shop, both Pennzoil's and Castrol's ATF are around the same price as their fork oils.

southwest US good synthetic ATF runs about 5$ a quart, fork oil about 12-15$

Important point for considering below is: "... ATF is also meant to provide a certain level of friction to operate specific transmission designs. Fork oil is designed to provide the lowest amount of friction to reduce static friction and wear, and improve damping consistency. ..."

atf is a much better lube than fork oil.it keeps transmissions running cool at today's engine speeds of 6500rpm and keeps seals pliable and tight.the friction you speak of is not in the fluid, they are called friction modifiers which are a chemical that when interacting with the tranny's friction clutch plates will alter the clutches friction materials to increase or decrease.theres no actual compound in atf to cause friction between metal on metal or metal on seals.