Racing Brake Fluid - Wrist Twisters
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  • 1 Post By badmoon692008
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post #1 of 6 Old 08-12-2018, 03:25 PM Thread Starter
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Racing Brake Fluid

I just installed some HEL stainless brake lines and flushed and replaced the brake fluid with
Motul RBF 660 Synthetic racing brake fluid.
While it works really good,I've heard that high temp racing brake fluids can break down fairly quickly,
as they're intended to be replaced on a regular basis.
Any truth to this, or will it just gradually break down, or is it OK to use.

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post #2 of 6 Old 08-12-2018, 04:35 PM
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Quote:
Originally Posted by Diablo View Post
I just installed some HEL stainless brake lines and flushed and replaced the brake fluid with
Motul RBF 660 Synthetic racing brake fluid.
While it works really good,I've heard that high temp racing brake fluids can break down fairly quickly,
as they're intended to be replaced on a regular basis.
Any truth to this, or will it just gradually break down, or is it OK to use.
It's a DOT 4 non silicone 'glycol based fluid as best as I can find.
So it will still be hygroscopic.
And be compatible with your seals.
Overkill for sure, re the temp capability of the fluid in a uncontaminated (no water absorbed) state.
My guess is that it won't even potentially see heat within 200 F of its 617 F rating in a 919 with stock pads (as are fitted with thermal break shims).
It should be A OK to use.
If you live in a humid area, don't let it go longer than 2 years without replacing it.
If in a humid area and doing track days or racing, annual change is a wise policy.

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post #3 of 6 Old 08-12-2018, 07:17 PM Thread Starter
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It's very hot and humid here, and I give the brakes a good workout through the tight steep corners around and through the hinterlands.
I was mostly wondering how the deterioration takes place, will they slowly become spongy.

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post #4 of 6 Old 08-12-2018, 08:00 PM
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Quote:
Originally Posted by Diablo View Post
It's very hot and humid here, and I give the brakes a good workout through the tight steep corners around and through the hinterlands.
I was mostly wondering how the deterioration takes place, will they slowly become spongy.
That spec looks to be valid for heat load from race application carbon/carbon near through to glowing.
My assumption is that the chemistry is stable to way beyond what your parameters could ever introduce in terms of heat load transmitted to the fluid.
In other words, I don't see how heat induced chemical decomposition or any kind of "morphing" would be possible.

Water ingress from hygroscopic effect though, will degrade it and the result is boiling point suppression.
And one can't visually tell any water has gone into solution. (unless the fluid has something in it to make it change colour from the presence of water, like Castrol Girling Green used to, any water in it made it turn blue).
Beginning stages is sponginess, then worse, then total loss of actuation.
(had it happen to me in a car once, total loss that is, not fun at all!)

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post #5 of 6 Old 08-13-2018, 07:08 AM
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As it's been told to me, the racing fluids work very well but as a result of being made to have a very high boiling point and high performance they also have more/faster deterioration as a result of absorbing moisture from the air and other breakdown. I run the RBF600 in my race bike with no complaints, although it gets changed out quite often, and the RBF660 is even one step further than that. It's not like it'll go from perfect to no brakes in one day, just keep an eye on it and it will likely need to be changed out sooner than a more standard brake fluid.

That being said, it's really not worth the extra money and shorter change interval to use any of these types of fluids in a street bike.

Hopefully @LDH will chime in with some further knowledge
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post #6 of 6 Old 08-13-2018, 10:38 AM
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All DOT3/4 brake fluid is hygroscopic. It will always extract moisture from the atmosphere and gradually degrade from its original properties.


Racing brake fluid does have its place as it is required to withstand the heat it can be subjected to at that level of use. I personally find that at the level I ride I can tell no verifiable difference between RBF6xx, Brembo grades, Castrol SRF, ATE or good ole Valvoline Syn-Power from Autozone at $2.99 a bottle. It all does the same job in the same manner.

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