Anyone try 2.5wt damper oil in Rockshox Forks? (factory is 5wt)

[droo]

Good thread this, some nice useful info.

 

All the knowledge in the world resides on the Hub. And not just about bikes.

 

All you need is a finely tuned BS detector...

[Skylark]

Any O-ring made for hydraulics, which most are, will work. Brake fluid and fork oil is basically hydraulic fluid. I just confirmed with each place that I went to look for the O-rings that they were suitable for hydraulics.

 

I had this mystical idea that the seals in my fork were magic, super duper special "fork" seals, well there are a few but the main ones in my Rev and many forks are not special, they are just normal O-rings. It turns out its just plain old fluids and mechanics in a fork - same things that power the equipment like diggers and cranes etc that build the world around us and they all need seals, mostly being O-rings. So cool!

[droo]

Yup. They're all 70 shore buna nitrile, which is a bog standard o-ring. There are a few places in shocks where you'll need 90sh, which are a bit harder, but for forks NBR 70 is fine in all cases.

[GoLefty!!]

Any O-ring made for hydraulics, which most are, will work. Brake fluid and fork oil is basically hydraulic fluid. I just confirmed with each place that I went to look for the O-rings that they were suitable for hydraulics.

 

I had this mystical idea that the seals in my fork were magic, super duper special "fork" seals, well there are a few but the main ones in my Rev and many forks are not special, they are just normal O-rings. It turns out its just plain old fluids and mechanics in a fork - same things that power the equipment like diggers and cranes etc that build the world around us and they all need seals, mostly being O-rings. So cool!

 

 

Be careful with stating Brake fluids are just normal oils. they can be but mostly they're not. Shimano Mineral Oil Brake Fluid is around an ISO 15, fork oils are slightly more viscous.

then theres hydraulic oils for systems that contain silver and for those without.

there are circulating oils which are not suitable for every application or seal type.

 

be very careful with generalisations.. All the seals are of the nitrile variety which are resilient to many materials

[droo]

Be careful with stating Brake fluids are just normal oils. they can be but mostly they're not. Shimano Mineral Oil Brake Fluid is around an ISO 15, fork oils are slightly more viscous.

then theres hydraulic oils for systems that contain silver and for those without.

there are circulating oils which are not suitable for every application or seal type.

 

be very careful with generalisations.. All the seals are of the nitrile variety which are resilient to many materials

 

Also, DOT brake fluid will swell nitrile seals - for these you'll need EPDM seals, which are a bit more difficult to find.

[GoLefty!!]

exactly. DoT brake fluids are NOT COMPATIBLE with anything else. DOT 3, DoT4 and DoT5.1 are interchangable but DoT5 is again not compatible with any of the others. Its a stand alone Silicone based brake fluid for race car braking systems.

 

 

With Mineral Oil brake systems, there can be severe performance loss if you opt for a different fluid than the one recommended. For Shimano brake systems I'd say stick with the Shimano mineral Oil brake fluid. Magura works ok because they use the same supplier but with different dyes (one is red the other blue) but the viscosities are not the same. For best performance the Shimano brake is designed around their version of the mineral oil. Other hydraulic fluids may not have the same constituents to ensure reliability.

 

E.g. the aromatics content in a minerla oil is important because this allows the seals to swell a little. An oil wth aromatics contents outside of 10% either way of the OEM product can cause the seals to swell further(increasing friction and causing premature seal failure) or cause the seal to shrink resulting in leaks, poor caliper brake clamping force and seal blow by resulting in brake failure.

 

End users choice.

[Skylark]

Ok I shouldn't have included dot brake fluid amongst others, why is brake fluid so corrosive?

[GoLefty!!]

Alkyl ethers of ethylene glycol or Diethylene glycols are highly corrosive i.e. they tend to be acidic. They are also good solvents and can soften certain plastics and rubbers hence the choice of seals is important with these fluids

[deanbean]

Excellent thread, thanks Drooo and Lefty. Always informative.

[Skylark]

Alkyl ethers of ethylene glycol or Diethylene glycols are highly corrosive i.e. they tend to be acidic. They are also good solvents and can soften certain plastics and rubbers hence the choice of seals is important with these fluids

 

Why specifically are they needed in brake fluid? They do something like help tweak the thermodynamics/increase the boil point of the fluid?

[GoLefty!!]

They are hygroscopic which means they can absorb water to an extent and still perform their function of transmitting force. The absorption of the water leads to a lower reflux boiling point and reduced performance but they can still function. Problem is water will increase the corrosive effects of the fluid.

 

Mineral oils in an automotive application are simply not good enough to provide the necessary performance at very high temperatures that these brakes need to absorb. Mineral oil is fine for our bikes because the operating temperature just never gets high enough for any water to be a major problem and there is no additional corrosive effects.