Brake fluid brand

[TVdawg]

I had been using the Valvoline "Synth Power" brake fluid in all my motorcycles for some time. I used the last I had recently doing a brake flush on my friend's RT and discovered it is no longer available. After a little research I discovered the Valvoline that you now find has lower specs than the "Synth Power," but is exactly the same as the BMW brand that most dealers use. I'm curious as to what many forum users have put in their systems. I'm also wondering if buying high end racing brake fluid would be overkill since I plan to change the fluid annually anyway. Thoughts?

[smiller]

Use any decent-quality DOT4 fluid. Changing it frequently will matter much more than any specific brand.

[Downs]

As long as it meets DOT 4 specs you are good to go. You could even substitute DOT 3 in a pinch they are compatible but DOT 4 has a higher dry boiling point than 3. Make sure the bottle is sealed and whatever you don't use dispose of. Sitting on the shelf it will suck up moisture out of the air.

 

Honestly any manufacture can call brake fluid "Synthetic". IIRC all brake fluid is Synthetic.

[philbytx]

Ate Typ 200 and SuperBlue. Alternate them on fluid changes...one is gold, the other blue. Just wait for the colour to change and "Voila!" It also has superior wet and dry boiling points .

 

[TVdawg]

The ATE is kind of pricey and I've heard the blue coloring will stain the resevoir. Still, I like the idea of changing the colors each flush but wonder if the price of the higher temp fluid is justified or necessary. I don't really care about brand as much as I want to find something I can buy off the shelf at the local auto parts store.

[Guest Kakugo]

Any DOT4 from a reputable brand will do. However don't buy the Castrol "Super DOT4". I run it for a while on my track bike and it degraded pretty quickly, requiring frequent flushes. The humble regular (and cheaper) DOT4 from Motul is much much better.

Otherwise just pop down the local Honda or Yamaha dealer and get their branded products: really, really good stuff.

[Peter Parts]

Maybe I am an insensitive klutz, but what makes brake fluid degraded? What do you experience as a rider that tells you the fluid is poor, old, bad, or whatever? What is working poorly that tips you off that you need to change the fluid (or that would tip you off eventually)?

 

(Aside from something boiling in the calipers... which has never happened to me that I know of. Or rusting in the calipers that I have never observed - because I never looked for it.)

 

Ben

[Michaelr11]

Maybe I am an insensitive klutz, but what makes brake fluid degraded? What do you experience as a rider that tells you the fluid is poor, old, bad, or whatever? What is working poorly that tips you off that you need to change the fluid (or that would tip you off eventually)? Ben

Brake fluid absorbs water from the air. The water is what degrades it; it lowers the boiling point and the water attacks the brake system components. You can see it by the color change of the fluid. When you flush with new fluid it is nearly clear. Look at yours, or go around a gathering and look at fluid in other bikes. You'll see some that are amber, some that are dark brown, nearly black.

 

My ABS-II system with speedbleeders is so easy to flush that I do it at least once or twice a year; takes about 5 or 10 minutes.

[Peter Parts]

Maybe I am an insensitive klutz, but what makes brake fluid degraded? What do you experience as a rider that tells you the fluid is poor, old, bad, or whatever? What is working poorly that tips you off that you need to change the fluid (or that would tip you off eventually)? Ben

Brake fluid absorbs water from the air. The water is what degrades it; it lowers the boiling point and the water attacks the brake system components. You can see it by the color change of the fluid. When you flush with new fluid it is nearly clear. Look at yours, or go around a gathering and look at fluid in other bikes. You'll see some that are amber, some that are dark brown, nearly black.

 

My ABS-II system with speedbleeders is so easy to flush that I do it at least once or twice a year; takes about 5 or 10 minutes.

Yup, that's the theory and sure enough, color changes.

 

But my question was whether it makes any difference in operation in reality and how would I notice it?

 

Can't say as I've ever noticed water coming out when I bleed.

 

(When I asked this before, I mentioned that nobody changes their car brake fluid any too often. But that will only lead to people explaining to me how different are bikes... in theory.)

 

Ben

[dirtrider]

Morning Ben

 

Moisture in brake fluid effects the wet boiling point. Same on a car, truck, or motorcycle.

 

If you don't ever use the brakes hard enough to generate enough heat to boil that moisture & turn it to steam then about the only thing that happens is some pitting in the brake system internal parts due to that moisture suspended in the brake fluid.

 

If you want to Quickly see how much moisture you have in your brake fluid just go make a spirited pass down Pikes Peak. That will not only generate lots of brake heat due to the down grade & curves but the lower atmospheric pressure at altitude will substantially lower the brake fluid boiling point. (reason I used to do some of my brake testing there)

 

Most (newer) cars & trucks have sealed brake systems but still some moisture can get in over time through the rubber in the brake hoses & other loosely sealed areas. The BMW bikes with the I-ABS systems (wizzy brakes) have the controller master cylinder reservoirs open to atmosphere through the vent hoses (in my estimation not a desired trait but it is what it is).

 

When BMW went to the Stahlflex brake hoses instead of the older rubber based they did issue a service bulletin that the bleed interval could be increased a bit as less moisture can get into the system through the Stahlflex brake lines.

 

[racer7]

Wrong information is starting to accumulate in this thread- too many only partly accurate comments

 

1) Yes brake fluids are hygroscopic but it isn't true that the discoloration you see is primarily caused by water or that minor amounts of water vapor in a sealed system have any significant impact on boiling point of brake fluids.

Discoloration is caused primarily by oxygen in the air. Many brake fluids are packaged and handled under a nitrogen blanket for this reason.

I own the tools for making boiling pint measurements on brake fluid and have made many hundreds of such measurements on track and street vehicles. Even very badly discolored fluid and stuff visibly containing moderate amounts of accumulated water vapor show no significant loss of boiling point. IMO, it is extremely unlikely (less than 1 chance in 1000) that you will ever find a situation on a street bike where boiling point is significantly degraded by water vapor. It might be useful to know that wet boiling points are determined after equilibration in a fully saturated atmosphere- a circumstance that will not occur in a closed bike system that has only a small reservoir vent. Many of the fluids I've tested have been 4 or more years old with no issues of any kind other than discoloration.

2) Yes DOT3 and DOT4 are chemically compatible (as is DOT 5 but not DOT 5.1) but I would be very careful about using DOT3. Not because of boiling point but because a number of these I've seen seem rather susceptible to forming gums- the precise thing that causes damage in BMW brake systems.

3) There are other relevant properties of brake fluid that impact the feel of the brake system. For example, fluid viscosity effects feel under trail braking. Not very important for street use but of interest to racers.

4) Anti-corrosion properties in brake fluid are the first thing that goes bad- caused by oxygen exposure. There are commercially available means to test for this..

 

The BMW DOT4 fluid has very good color (about as close to water white as any readily available fluid) and is well packaged in a suitable size. Its also not expensive. Other DOT4s are also usable but I wouldn't use anything else except in a true emergency situation and then would remove/flush ASAP. But if using an alternate DOT4 I'd pay particular attention to its age and proper packaging and avoid it if showing any type of discoloration. Bike do not have the temp issues encountered by race cars or fast street cars because bike brakes and calipers run cooler so emphasis on highest boiling point is irrelevant...

 

For many years I used Motul 600, a DOT 4 rated racing brake fluid in everything except my bike because I bought it by the case and used it in track machinery that got a full brake flush for every event (it also had the highest available boiling point at that time except for Castrol's hugely expensive SRF which did not carry a DOT rating). But because Motul 600 color got worse faster than some others I kept the BMW fluid in the bike...

 

[dirtrider]

Wrong information ---2) Yes DOT3 and DOT4 are chemically compatible (as is DOT 5 but not DOT 5.1) ---

 

Careful here-- DOT 5 is a silicone-based brake fluid & is NOT compatible with Dot 3 or Dot 4.

[philbytx]

I believe (hope!) he may have transposed it DR. As you stated, Dot 5 is silicone based and NOT compatible but DOT 5.1 is DOT4 compatible

[lkchris]

Honestly any manufacture can call brake fluid "Synthetic". IIRC all brake fluid is Synthetic.

 

It for sure does not occur naturally in nature.

[tallman]

We always told customers it was a form of preventative maintenance, particularly in our high humidity area, to help protect the brake system BMW used (pre new system) as replacement costs associated with the ABS were extreme.

YMMV

 

[Peter Parts]

The man with the data says up to four years sort of, and much other information too.

 

THANKS for exemplary post, racer7. You both communicated your information very clearly but also clear in your emphases.

 

I can see Tallman's POV too.

 

Always puzzled me why BMW (or owners like us) didn't just say "5.1 forever" once it was available and thus settle matters there. Any shortcomings to 5.1.... sounds ideal and maybe even permanent?

 

Ben

[TVdawg]

Thanks guys. This is the discussion I was hoping for. Since my original post, I've discovered Pentosin Super Dot4 is available at the local auto parts stores and is reasonably priced. It has a higher wet and dry boiling point and moisture resistance. Think I'll give it a try.

[philbytx]

For those statistic addicts:

 

 

Dry boiling point Wet boiling point

DOT 3 205 °C (401 °F) 140 °C (284 °F)

DOT 4 230 °C (446 °F) 155 °C (311 °F)

DOT 5 260 °C (500 °F) 180 °C (356 °F)

DOT 5.1 270 °C (518 °F) 190 °C (374 °F)

 

Ate Typ 200 exceeds all the above.

It has a Dry boiling point of 536 deg. F, and a wet boiling point of 396 deg. F

 

So, given the higher wet boiling point of the Ate, and if you were feeling particularly carefree and were not as anal as I, you could keep the Ate in your system a little longer .

 

Although using a superior product, I still run 2 year changes on cages and bikes. Then again, I am entirely anal