Racing Brake Fluid

[rawky]

How is this better than bog standard stuff? Surely different liquids can't compress more or less?

[belleair302]

5.1 brake fluid resists a chemical breakdown more slowly under heat and also absorbs less moisture from external sources. However it does need replacing but will help with better brake feel when a car is driven hard if all of the pipes are also replaced if old.

[anonymous-user]

They usually have higher dry boiling points, sometimes at the expense of wet boiling point. Motul RBF600 for example has a dry boiling point of around 600°F so can resist more heat from the brakes before it boils. When it boils it becomes gas which is compressible. The wet boiling point is what temperature the fluid will boil at when it's absorbed moisture. Fluids can apparently be more or less compressible too - this is one of the downsides to Dot 5 silicon fluid. Super Dot 4 can be as good for this as 5.1 in many cases. The aforementioned RBF600 is a Dot 4 despite exceeding the dry and wet boiling points for Dot 5.1, but certain specs don't pass (low temp viscosity IIRC).

[jonamacg83]

Worth mentioning you should never use DOT 5 ina car. The silicon base would cause all sorts of problems. DOT 4 or 5.1 only.

Jonny

[Mr2Mike]

jonamacg83 said:

Worth mentioning you should never use DOT 5 ina car. The silicon base would cause all sorts of problems. DOT 4 or 5.1 only.

Jonny

You certainly can use it in a car (what else would you use it in?), provided the system has never had mineral based fluids in it. DOT 5 however, is utter crap in most respects and should be avoided.

[porscheuro]

porsche run their cars on dot 4 this eems good enough

[ridds]

Ran 5.1 in my Cerb and lost brakes at Spa. Was only a year old as well.

May go back to 4.1 and give that a try.

[tr7v8]

Mr2Mike said:

jonamacg83 said:

Worth mentioning you should never use DOT 5 ina car. The silicon base would cause all sorts of problems. DOT 4 or 5.1 only.

Jonny

You certainly can use it in a car (what else would you use it in?), provided the system has never had mineral based fluids in it. DOT 5 however, is utter crap in most respects and should be avoided.

Interesting comment, based on what experience? Designed for & used by the US military & I know loads of classics that use it. Their also used to be a Caterham racer using it (Mike Bees) all without any problem.

[lookout]

As Lexsport says, mainly boiling point related.
Though, in my experience, DOT5.1 can produce some problems as the viscosity is different, and can produce a soft brake pedal.
I use Castrol SRF. Hellishly expensive compared to other fluids but resists boiling better than other fluids and great pedal feel.

[The PM]

The 5.1 is much better than 4, but as it's desgined for racing it needs to be changed far more than 4

[Munter]

The PM said:

The 5.1 is much better than 4, but as it's desgined for racing it needs to be changed far more than 4

Find a book on the subject. Read the threads on Brake Fluid. Come back and think about what you just said.

[Mr2Mike]

tr7v8 said:

Mr2Mike said:

jonamacg83 said:

Worth mentioning you should never use DOT 5 ina car. The silicon base would cause all sorts of problems. DOT 4 or 5.1 only.

Jonny

You certainly can use it in a car (what else would you use it in?), provided the system has never had mineral based fluids in it. DOT 5 however, is utter crap in most respects and should be avoided.

Interesting comment, based on what experience? Designed for & used by the US military & I know loads of classics that use it. Their also used to be a Caterham racer using it (Mike Bees) all without any problem.

1) It has an amazing ability to retain tiny air bubbles, so it can make bleeding difficult and you rarely get as good a pedal as you would with mineral fluid.
2) If any water gets into in the system it tends to sink to the lowest point in the system i.e. the calipers which is the very worst place for it to be.
3) The molecular size of silicon fluid is smaller than mineral, which means it's more difficult to seal, compounded with the fact that a lot of seals do not swell up with silicon as they would (and should) with glycol.

Have a look at A.P. Racings website, they specifically state that they do not recommend silicon fluid, and Brembo recommend DOT4 for their systems. I'd hope they know what they are talking about.

[anonymous-user]

Military and classic use also has very different priorities than racing - longevity as opposed to ultimate performance. Because Dot 5 is not hygroscopic, it doesn't need replacing like Dot 4/5.1 However, as mentioned, because it doesn't absorb water it stays as water and can cause corrosion of pipes from the inside out, so perhaps not quite the "fill and forget" solution people want.

[Paul Drawmer]

Probably worth mentioning that usually the higher temp the boiling point of a brake fluid, then the more often it will need replacing due to its absorbsion of water. SRF is very very good at very high temps, but it does need replacing, else that amazing performance will fall.

I've heard that some serious performance users will replace SRF after every event!

I've settled on RBF600, and change it every year.