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Discussion Starter #1
A friend of mine read in a Chilton's repair manual that you shouldn't mix brands of DOT4 brake fluid.
I don't see why it would make any difference as long as both brands are DOT4.
Anyone ever heard of this?
Thanks,
Ralph Wenzl
 

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I'm not sure if I would mix DOT 4 regular with DOT 4 synthetic....But,
thats just me. If both were DOT 4 even different brands, I see no problem
mixing them. No different than mixing BP and Shell gasoline.
 

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Simple - you mix DOT 4 with DOT 3 and you have DOT 7. DOT 4 with DOT 4 and you have DOT 8. I learned dat in first grade. And you should not use DOT 8 in a Goldwing.
 

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Simple - you mix DOT 4 with DOT 3 and you have DOT 7. DOT 4 with DOT 4 and you have DOT 8. I learned dat in first grade. And you should not use DOT 8 in a Goldwing.
NO NO NO if you mix DOT 4 with DOT 3 you get DOT 43. :joke:
 

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A friend of mine read in a Chilton's repair manual that you shouldn't mix brands of DOT4 brake fluid.
I don't see why it would make any difference as long as both brands are DOT4.
Anyone ever heard of this?
Thanks,
Ralph Wenzl
There are standards written that document what makes up different brake fluids. DOT 3, 4, 5 & 5.1 have their own specifications. There should not be any issues mixing one brand of DOT 4 with another, as long as the same standard was in place at the time that particular bottle was made. As I understand it, all DOT 3 & 4 today is synthetic.

That said, someone recently found a bottle labeled to indicate non-synthetic DOT 3 and a bottle of non-synthetic DOT 4 on a store shelf. Not sure whether this was old stock or just an old labeling system. DOT 3, 4 & 5.1 fluids are polyethylene glycol based. I am also not sure whether or not DOT 3 was polyethylene glycol based 15 years ago, but just not called synthetic.:shrug:
 

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Why even consider jeopardizing your life and bike performance over a $5.00+- product? I just don't get it? :shrug:
 

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Mixing DOT three with DOT four results in a factor determined by [the square root of (the square of three plus the square of four)]. Thus five. Didnya guys learn noth'n in algebra class?

Seriously, there may be no chemical disagreement; but why do that? Unless you have a leak, there is no reason to top-up brake fluid and a very good reason not to.

prs
 

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The bike comes with DOT 4 installed, but who knows what brand Honda used during the manufacture. The best you can do when flushing & bleeding is make sure it is DOT 4. And since I use synthetic for all fluids I use, that's what goes in with what ever Honda used.
 

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flush out and use fresh DOT4
 

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There are standards written that document what makes up different brake fluids. DOT 3, 4, 5 & 5.1 have their own specifications. There should not be any issues mixing one brand of DOT 4 with another, as long as the same standard was in place at the time that particular bottle was made. As I understand it, all DOT 3 & 4 today is synthetic.

That said, someone recently found a bottle labeled to indicate non-synthetic DOT 3 and a bottle of non-synthetic DOT 4 on a store shelf. Not sure whether this was old stock or just an old labeling system. DOT 3, 4 & 5.1 fluids are polyethylene glycol based. I am also not sure whether or not DOT 3 was polyethylene glycol based 15 years ago, but just not called synthetic.:shrug:

Me thinks you are mistaken, I just bought a bottle of DOT 4 and it is not synthetic. They still make it and also synthetic
 

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Why even consider jeopardizing your life and bike performance over a $5.00+- product? I just don't get it? :shrug:
You're talking to a bunch of dimwits that risk screwing up their engine all the time over an oil filter and a gallon of oil. Don't waste your time.
 

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Discussion Starter #14
The original question (paraphrased) was "Can DOT4 brake fluid from manufacturer X be mixed with DOT4 from manufacturer Y?

No one's life is in danger and no master cylinders were harmed in the making of this question. LOL. Some of you guys sure love drama though.

My friend is planning to bleed his brakes sometime this summer and the Chilton manual said not to mix DOT4 with any other DOT number (duh) and also not to mix it with another brand of DOT4. Kind of hard to not mix brands when the bike is bought used and you don't know what brand is in the bike now. Plus it sounds absurd to me that two different brands couldn't be mixed. That's why there are standards such as "DOT 4" in the first place. Still, I thought I'd ask the question on this board on the slim outside chance that there's some chemical reason not to mix brands.
Thanks,

Ralph Wenzl
 

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The original question (paraphrased) was "Can DOT4 brake fluid from manufacturer X be mixed with DOT4 from manufacturer Y?

No one's life is in danger and no master cylinders were harmed in the making of this question. LOL. Some of you guys sure love drama though.

My friend is planning to bleed his brakes sometime this summer and the Chilton manual said not to mix DOT4 with any other DOT number (duh) and also not to mix it with another brand of DOT4. Kind of hard to not mix brands when the bike is bought used and you don't know what brand is in the bike now. Plus it sounds absurd to me that two different brands couldn't be mixed. That's why there are standards such as "DOT 4" in the first place. Still, I thought I'd ask the question on this board on the slim outside chance that there's some chemical reason not to mix brands.
Thanks,

Ralph Wenzl
Ralph:

By the time a batch of polyethylene glycol meets the DOT 4 spec, I suspect that it doesn't matter where the feedstocks came from - synthetic v. organic probably makes no difference.

However, your friend might note that the bike is used, and he'd likely be surprised by the amount of gunk that can languish unseen in your brake system. It doesn't take hardly any more time to refill the whole system instead of just bleeding it a bit. Do the whole thing with one brand of new fluid and sleep soundly at night.
 

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Discussion Starter #16
Ralph:

By the time a batch of polyethylene glycol meets the DOT 4 spec, I suspect that it doesn't matter where the feedstocks came from - synthetic v. organic probably makes no difference.

However, your friend might note that the bike is used, and he'd likely be surprised by the amount of gunk that can languish unseen in your brake system. It doesn't take hardly any more time to refill the whole system instead of just bleeding it a bit. Do the whole thing with one brand of new fluid and sleep soundly at night.
Yes. That's the plan. Only asked because of what he read in the Chilton manual.

Ralph Wenzl
 

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You guys are all wrong DOT 4 and DOT 3 leave you with DOT 1. It is a subtractive process not geometric or additive.
 

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:cool: Gosh, DOT 12,8,43,and one. Lol!

All DOT 4 synthetic or not are compatible with each other. Says so right on the bottle, and besides they would not put it on the market if not. There is always a bit of whatever brand left in the system even with a full flush. Kinda like changing the oil, you never get it all out.
But I would use a good synthetic DOT4. I know I used Prestone DOT 4 synthetic last time and I have been watching the little sight glass window, still clear, had not changed to amber yet, that was a year ago.

Synthetic does not seem to draw moisture as fast.

Kit
 

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I admit up front that I am not an expert in brake fluids, but one thing I have read in the instructions is to always use the same DOT rating fluid and to use fresh brake fluid when adding fluid or changing it out i.e. flushing the system. The reason is that most brake fluid is hydroscopic, meaning it has an affinity for water and sucks it up out of the atmosphere if given half a chance. With water suspended in the fluid, it causes a couple of problems. First, it can start to corrode the parts in the brake system, the master and slave cylinders being the prime candidates but rubber brake lines can also start to degrade. The other problem it causes is that as the brakes are used hard, they generate extreme heat, some of which gets transferred to the brake fluid. If there is water in there, the heat causes it to expand and that can cause the brakes pads to be pressed against the rotors without the brake lever/peddle being applied.

The latest class of brake fluid (5.1?) is suppose to be made of stuff that is not hydroscopic so it is not subject to either of these problems, but I am not sure which specific class it is. You should look at the brake fluid reservoir and see which class fluid is specified, and only use that type for replacing or flushing your brake system. You should never mix the two. Even converting a system from one type to another is not advised because components are selected to work with a specific type and may be damaged or fails if exposed to another type of fluid. If you feel you must change from one DOT rating fluid to another, I recommend that you completely break down your entire brake system and clean it throughly before adding the new fluid.

My personal criteria for old brake fluid that has its seal broken is to throw it out if a) it is more than a year old and was filled near the top, or b) if it is more than six months old and less than half full. If it still has its seal in place, I would use it even if it was three to four years old. After that...not sure if I would use it or dispose of it. For any brake fluid that I am considering using that comes from a container that has a broken seal, I pour some in a clear glass container and look at the color and give it a smell. If it is cloudy or has any weird or strong smell to it, I dispose of it and get a new bottle. I live in a very dry climate so those living in humid conditions might want to reduce the above stated time limits.

Hope this was helpful and I appologize for not joining into the non-sensical banter about what you should call brake fluid that is a mixture of DOT 3 and DOT 4. :rolleyes:
 

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Why even consider jeopardizing your life and bike performance over a $5.00+- product? I just don't get it? :shrug:
I just don't get it translates to I don't actually understand it which causes you to fear doing it. If you understood it, you would realize that there is nothing wrong with it. Of course then you would get it.
 
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