Racing Brake Fluid - Wrist Twisters
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post #1 of 7 Old 08-12-2018, 04:25 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 7 Old 08-12-2018, 05:35 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 7 Old 08-12-2018, 08:17 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 7 Old 08-12-2018, 09:00 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 7 Old 08-13-2018, 08:08 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 7 Old 08-13-2018, 11:38 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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post #7 of 7 Old 10-02-2019, 04:18 PM
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Which DOT spec' Brake Fluid to use in Motorcycles

Quote:
Originally Posted by LDH View Post
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.
Thread resurrected as triggered by present KarlJay's circumstances of using 4 instead of 5, in an effort to link some good info about brake fluids.

Next are some relevant extracts from the present thread "Going to redo the front,......"

DOT 5 is silicone based and highly incompatible for the 919 brake system.
Given the nature of the 919 brakes, variant DOT 5.1 is of no real advantage.
Suggest you stick to DOT 3 or 4.
Perhaps the 5 you are getting, is actually 5.1.
--------------------------------
DOT4 is what you want.
From Motorcyclistonline.com...
https://www.motorcyclistonline.com/m...des-explained/
"If youíre thinking DOT 5 sounds really appealing right now, think again. DOT 5ís price, as well as its compressibility and viscosity, make DOT 5 unsuitable for use in motorcycles. So why does it exist? It was created for the military to use in vehicles that will be parked for years at a time. Harley-Davidson used DOT 5 until a decade ago but specifies DOT 4 now that all their bikes have ABS."
--------------------------------
I'm wondering why they would sell the DOT5. Pretty easy for someone to just grab the highest number. I wasn't even using DOT4 until I noticed that the cover said DOT4. I was mainly concerned with the boiling point and what happens when you mix things. I didn't want seals to go bad because of mixing types.
-------------------------------
Odd to me is a biz with a motorcycle specialty sound name even has 5 on the shelf, let alone markets it.
Then I see how BelRay depicts a motorcycle front brake on their label.
Is it supposed to suggest a H D of some vintage?
Does anyone know of a current model by any maker that calls for DOT 5?
Also, the BelRay website says without any qualification that it's A OK to flush out 3 or 4 and put in 5.
Not 5.1, but silicone 5.
REALLY?
--------------------------------
I've just started some fishing about on all this, and just stumbled upon the following link re Brembo items.
Here's the salient point extract verbatim:

Brembo Technical Notes

B. All brembo braking products use natural-rubber base seals, and therefore are INCOMPATIBLE with DOT-5 SILICONE-based brake fluids. DOT- 5 SILICONE-based fluids react with natural-rubber seals to swell them WHICH CAN CAUSE SEVERE PISTON RETRACTION PROBLEMS. There is no cure for problems caused by DOT- 5 use other than complete seals replacement - USE ONLY DOT-3/4 NON-SILICONE TYPE FLUIDS such as CASTROLTM 'LMA' in your brembo components.(Yes, we know the cap on the rectangular master cylinders says "DOT 3 - 5 Fluids"-BUT PLEASE NOTE: Silicone DOT- 5 fluids are NOT generally in use in Europe, but Glycol-based "DOT-5.1" fluids ARE. Hence, the "DOT-5" cap designation). For best braking performance, we recommend changing brake fluid twice a year. If the machine is to be stored in a damp environment (over the winter, say), we recommend installing fresh fluid before and after the storage period. At minimum service levels, glycol brake fluids MUST be completely changed at intervals not to exceed a period of 18 months.


Note A was also a wake up call, in terms of mixing a Brembo master with Honda OEM calipers. I'll have to keep this in mind when I finally move ahead on getting a Brembo master (not the banjo aspect, aside from using the correct bolt) to go with the F4i calipers I still have not yet put on:

A. All brembo braking products use a 1.0mm x 10.0mm thread pitch for hydraulic fittings. (Honda, ISR, Kawasaki and Yamaha use 1.25mm x 10.0 thread pitch for their fittings, Suzuki use 1.0mm x 10.0mm). Be aware of this when using brembo components with your machine. Always use fresh copper or aluminum sealing washers when installing new or reinstalling old components.

Here's the link:
Brembo Tech Info
My understanding is that the Brembo Technical Notes are aNorth Americanised translation of an original Italian document, with some elaboration to address the inherent conflict of some of the DOT markings on certain Brembo components.

If anyone has factory info re current era sport bikes they have, I'd love to see what the other manufacturers have been calling out for the last 10 years or so.

Particularly interesting will be to see what DOT fluid is being called up for ABS equipped bikes, and my guess is 5.1.

Good quality DOT 4 looks to be the best choice default, aside from Harley D's from a certain era, while being wary of any ABS application and certain of using only the DOT fluid specified by the manufacturer.

The above also dovetails with what I was able to recently glean from a high level source out of motorcycle racing world.

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