DOT 5 Brake Fluid

Aris

DOT 5 Brake Fluid

Post by Aris »

Hi everybody. Ι am rebuilding the brakes of my 79 Z and am seriously tempted to use DOT 5 (silicone based) brake fluid. I have used this brake fluid in other classics with very good results but not on my Z. Any opinions, suggestions or warnings?

Thanks a lot

Aris :)

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Post by Jim-Jim »

Well, I've read of two schools of thoughts on the Dot 5 fluid. One is that, since it does NOT absorb water as the others do, any water in the system settles to the bottom of the system, which is the calipers and corrodes all the parts within. The other is that you avoid this problem by changing the fluid on a regular basis. To me it seems that if you have to change the fluid to avoid water accumulation, then what have you gained? There are a couple of brands out there that are rated better than 3, 4, or 5 for boiling temp and absorb water (which means that you still have to change regularly) that would otherwise damage the caliper components. :roll:

But you use it in other bikes; there is nothing in the 'X' that is different as far as brakes go and, unless you are a hard charger, the heat factor would be no different than others so go with what you feel works well.

But, I think, others will have their own opinions, so read on. :wink:

Aris

Dot 5 Brake Fluid

Post by Aris »

Thank you Jim-Jim for a prompt answer. :)

The idea that water still accumulates in Dot 5 systems is certainly news to me!

I always thought that alcohol based fluids are hygroscopic and it is THIS characteristic which leads to the absorbtion of water from the environment, with the well known corrosion effects.

Silicone based Dot 5 fluids are NOT hygroscopic so water, if not present in the first place, would not normally enter the system at all. :wink:

What really still makes me hesitant about Dot 5 is WHY it has not been universally adopted by the rest of the motor industry, and why still expensive high end cars and bikes go with conventional, alcohol based fluids. Is it only the somewhat lower boiling temperature of the former or something else as well? :?

Regarding hard use of our classics, well.... not me really.

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Post by Jim-Jim »

Well, you raise an interesting point - I don't think that the alcohol base stuff reaches out and draws water from the outside (but I would like to hear some expert thoughts from someone) but absorbs condensation type water that gets in (but that makes me wonder how that occurs, also). I have read several items in both car and motorcycle pubs that mention that water does not get absorbed in Dot 5 and does in the other Dots, so it settles at the low points and corrodes - but - I don't recall (could be my senior moment) them saying how the water got in there in the first place. I need to go do some research; it is an verryyyy interrresting.

Maybe someone else has expert information. :shock:

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DOT 5 Brake fluid

Post by jimvh2 »

I bought a 79 and it already had DOT 5 in it. Compared to my other bike the pull of the brake seem smoother and more responsive. DOT 5 also has a higher boiling point than 3 or 4.(that's how the moisture gets in there). Since DOT 5 is silicone based, it will not hurt your paint. I'm thinking strongly about putting DOT 5 in my other bikes.
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Post by Mike Nixon »

Jim touched on something I want to expand on to be sure that the point is understood. Almost all OEMs use glycol brake fluid (Buell and Harley are exceptions, some of the clones also I think, I don't know who else) for an important reason. The simple fact is, most riders aren't EVER going to change their fluid. That is just a fact, as odd as it seems. (You don't know about these people, you say? Who do you think that huge rear brake was made for, expert riders?) For this majority, glycol fluid is safest and keeps the manufacturer from liability. Yes, glycol fluid has drawbacks -- it does indeed draw moisture out of the air, that's why you're not supposed to use fluid that has been open more than a couple months. But this hygroscopicity is a side effect from its being alcohol based, and is in fact what makes the fluid good for the average bike owner -- moisture in the system gets spread evely throughout instead of collecting in pockets to corrode the parts. Amalgamation, the engineers call it. Silicone based fluid doesn't do that. Silicone is also is far more prone to aeration. Harley-Davidson prescribes that a bottle of fluid that has been carried home from the store be allowed to sit for an HOUR before it is used, as it tends to aerate badly and is therefore full of bubbles. Of course, glycol fluid strips paint, where silicone does not, but that is a maintenance issue. There is also some legendary question of brake system firmness, but the supposed superior firmness of silicone fluid has never been quantified. It's very likely that the service of changing the fluid results in any possible firmness improvement, not the fluid itself. The bottom line is this -- glycol fluid, though technically a less performing variety, is far more consumer friendly. Silicone fluid is not at all consumer friendly, and you MUST change it often for it to be safe and to avoid maintenance issues, whereas as I say, glycol can be neglected indefinitely (it plainly is in the most cases), with no devastating effects. Interestingly, the issue is no longer which is more fade-resistant, as the newest glycol fluids perform as well temperature-wise as the glycols.

Aris

Dot 5 fluids

Post by Aris »

Hello every body, :D

as I started this thread I would like to remind us all the ONE REASON :oops: for which I for one, would consider Dot 5 brake fluids.

That is due to my perceived notion that Dot 5 needs to be changed less frequently than conventional, glycol based fluids. I have a number of classics (2 cars, 5 bikes) which average out less than 300 miles per year each! :? A fluid type which I should change every say 5 years, would make a lot of sense and I was considering Dot 5 for exactly this reason. If this is not so, then I too would not bother.

By the way, what does Harley & Buell prescribe as their (Dot 5) fluid change intervals for their bikes?

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Post by Mike Nixon »

Aris -- Thanks for reminding me that I did not address your actual question (only the comments of others on the board). I'll get to that in a bit, but first, silicone fluid (DOT 5) needs to be changed SEVERAL TIMES as often as glycol, so if you are looking for less maintenance, don't use it. As for its compatibility with the CBX's parts, it's generally agreed that seals that have been used with glycol be replaced before silicone is introduced, but it's not a hard and fast rule. But then you know that already, since you have used it several times in other vehicles.

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Post by Jim-Jim »

OK, it's not the original intent of the thread but now my curiosity is up and full blown. Considering a fresh brake system just topped off with glycol fluid (Dot 3, 4, etc) and bled nicely and all sealed off. Before I go charging off researching, HOW does water get into the system???? :?:

Does it 'osmosis' through the brake lines (rubber)? Or is it already in the fluid from the minute you open the can? I know the glycol absorbs it but how does it get in there in the first place? When we talked about the water settling out of the silicon fluid, the same question popped into my head - HOW does the water get in? Someone earlier said that the 'boiling' was how the moisture got in there in the first place but I don't follow the logic of that. If true, please diagram it out for my old, tired eyes. My truck has solid metal piping for the brake lines and I don't hear about water in those. So, I'm very, very curious. Knowledge leads to understanding and I want to understand this. :lol:

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Post by Mike Nixon »

Jim -- There is water in the air, and the brake system is not a closed system. It has a vent to atmosphere, remember, or it wouldn't work. Remember that an opened container gets water in it, and that is why you aren't supposed to use fluid from a container that has been opened over a certain period. Well, the situation is even worse with brakes, becauase you have the heat cycling. All brakes do this, that's why the fluid changes color. The degree of color change is relative to the amount of water.
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brake fluid

Post by c5 »

My guess to how water gets in the system is Condensation. Anytime there is air space(such as the fluid resovoir), there is room for this to occur. I'm sure climate conditions such as temp and humidity affect the rate and amount of condensation. Wow! That almost sounds scientific! But I'm just a dumb MT farmer so I'm probably wrong!

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Post by Passx »

Guy's,



I work for one of the major OE brake suppliers and can tell you that Mike is right in that all systems are vented otherwise you would have the brakes apply in hot weather due to the fluid & air expansion and then have a lot of travel in cold for the converse reason, if you look at the diaphragm under the cap and stretch it slightly you will see a slit and that's how things are vented on most systems and Mike is also right in that DOT 3+4 will literally pull the water out of the air whereas DOT 5 will not but will alow it to puddle in the bottom of whatever it's in. Lower maintenance ? either should be changed yearly and generally is outside of the U.S. we suck at this particular maintenance item, major differences are higher temp capabilities with DOT5 and then Dot 4 and DOT3 although there is some new 3 that has close to 5 capability. DOT 5 has less lubricity than the others and what that means is that your seals will wear out sooner with DOT 5 but if all is well not for a very long time. Typical ambient life cycle testing per SAE standards call for a 500k minimum cycles (based on a 10 year normal vehicle use) and either will do that but the DOT 5 seals will show more wear upon inspection. To convert to DOT 5 the system MUST be disassembled and clean or you will find things jelled from the mixing of the 2 fluids and eventually things will not return resulting in dragging brakes, just flushing will not accomplish this, sorry. Anyway that's my .02



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Post by Passx »

Guy's,



I work for one of the major OE brake suppliers and can tell you that Mike is right in that all systems are vented otherwise you would have the brakes apply in hot weather due to the fluid & air expansion and then have a lot of travel in cold for the converse reason, if you look at the diaphragm under the cap and stretch it slightly you will see a slit and that's how things are vented on most systems and Mike is also right in that DOT 3+4 will literally pull the water out of the air whereas DOT 5 will not but will alow it to puddle in the bottom of whatever it's in. Lower maintenance ? either should be changed yearly and generally is outside of the U.S. we suck at this particular maintenance item, major differences are higher temp capabilities with DOT5 and then Dot 4 and DOT3 although there is some new 3 that has close to 5 capability. DOT 5 has less lubricity than the others and what that means is that your seals will wear out sooner with DOT 5 but if all is well not for a very long time. Typical ambient life cycle testing per SAE standards call for a 500k minimum cycles (based on a 10 year normal vehicle use) and either will do that but the DOT 5 seals will show more wear upon inspection. To convert to DOT 5 the system MUST be disassembled and clean or you will find things jelled from the mixing of the 2 fluids and eventually things will not return resulting in dragging brakes, just flushing will not accomplish this, sorry. Anyway that's my .02



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DOT 5 Brake fluid

Post by busaboy »

I have used silicone in all my vehicles for about 20 years now, and I don't change them as often as I should - maybe every three years or so.



I like it because it doesn't strip paint (don't forget, even a small, slow seep that you didn't notice for a while will leave a nice, paint-stripped area where it lay), and the fact that it isn't hygroscopic. I don't notice any water accumulation when changing the fluid, and I certainly have not had any corrosion in any of my vehicles, most of which sit a lot.



I MAY notice a slightly less firm brake feel compared to glycol-based fluid; if it's there, it's very slight.



I have read in several vehicle shop manuals that it should not be used in ABS systems, probably because of its greater tendency to aerate - that certainly makes sense to me. Other manuals' vague, dire warnings to "...never use silicone-based brake fluids..." have caught my attention, but there never seemed to be any reason behind it. I have heard that many years ago, some silicone fluids had consistency problems which could foul up some brake systems.



Silicone can sit in the closed jug for a long time - I even remember from recent Army maintenance manuals that closed containers of the fluid are good indefinitely, even if the fluid loses its reddish-purple color.



Harley has specced it for many years in their new bikes; I think there are a few higher-performance cars that use it, but I can't name them.
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Post by Mike Nixon »

ABS systems use 5.1, a high-temp, but normally lubricating glycol fluid made specially for them.

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