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.
"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.
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.