Dot 5 Brake Fluid?

[Tartan Terror]

I see in a couple of posts that some people are very adament about not using DOT5 brake fluid. I have been using it for well over a year on the RSV in the clutch and front and rear brakes as well as in the front a rear brakes on my 1997 Honda Shadow ACE for about 4 1/2 years. I have had no problems, leaks, loss of brake strength or anything to indicate this is the wrong stuff. I do know that you need to be careful and not mix any different types. Please explain why you feel that this is so wrong. If Im headed for trouble I would like to fix it before but it should have happened already if it was.

[Snarley Bill]

I see in a couple of posts that some people are very adament about not using DOT5 brake fluid. I have been using it for well over a year on the RSV in the clutch and front and rear brakes as well as in the front a rear brakes on my 1997 Honda Shadow ACE for about 4 1/2 years. I have had no problems, leaks, loss of brake strength or anything to indicate this is the wrong stuff. I do know that you need to be careful and not mix any different types. Please explain why you feel that this is so wrong. If Im headed for trouble I would like to fix it before but it should have happened already if it was.

i think the only difference is dot 5 is silicone base and 3&4 aren,t .dot 4 has a minumum wet boiling point of 311 degrees,dot 3, 294, and dot 5 is 500 degrees f .and 3 & 4 don't mix with dot 5. don't know if dot 5 will affect the rubber brake parts.the soft parts of brake systems specifying dot 5 may be made of a different material.i would go with the recomendations of the manufacturer on brake fluid. bill

[Tartan Terror]

Ok guys. Here it is. I have done lots of research and this is what I have found. Dot 3,4,5.1 are of the same chemical base and are compatable. They will mix. Dot 5 is of silicone base. Can be used the same but if you use it you MUST make sure that all other type of fluid are evacuated first. If not it will gel and get lumpy. I have contacted Afco and EBC to get this info.

 

http://www.afcoracing.com/tech_pages/fluid.shtml

 

As I said I have Dot 5 in both my bikes and am using steelbraid lines and have had no problems. Water will be absorbed in 3,4,5.1 fluid but stay seperate in Dot 5. Over time in may cause problems but not immediately. We are talking years. As in the case with regular fluid it must be changed and bled. If you are using Dot 5 you cannot mix. If you mix any of the others accidentally it will not cause problems.

[BuddyRich]

Thanks Scott, That clears it up a bit. I was wondering why there was a 5.1

[Gary N.]

I have used dot 5 in my '32 Ford street rod since 1984 with no issues at all. (4 wheel drum brakes) Best part about it is it won't hurt the paint if you happen to get a leak or spill some.

[Snarley Bill]

before i posted my previous thread i tried mixing dot.3 and dot. 5, you are right the don't mix .never heard of 5.1 maybe it was an upgrade of five so it would be compatible with other fluids.bill

[Tartan Terror]

before i posted my previous thread i tried mixing dot.3 and dot. 5, you are right the don't mix .never heard of 5.1 maybe it was an upgrade of five so it would be compatible with other fluids.bill

No, 5.1 is an upgrade to 3 and4. Dot 5 is very different. Do not mix 5 and 5.1. 5 is silicone and 5.1 is standard. The dot rating is just that- a rating and not reflective of the material it is made of.

[Guest faz]

I did some research on the DOT5 as well after the replies to my post in 1st gen tech talk, and found some useful info in the following:

 

Here is an informative link on a ducati list:

Everything you should know about brake fluid

 

 

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... and here is the link for the article below: Battle of the DOTs

DOT 3-4 Verses DOT 5. Which brake fluid should I use?

 

From Oak Okleshen #35 "With regards to the DOT 3-4 verses DOT 5 brake fluid controversy, here is an article sent to me by Mr. Steve Wall. It is one of the most professional treatments I have seen on the subject".

[i had to condense this article from 6 pages to 1 due to space limitations -ed]

Brake Fluid Facts

by Steve Wall

As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:

1. Fluid compatibility with the brake system rubber, plastic and metal components.
   
2. Water absorption and corrosion.
   
3. Fluid boiling point and other physical characteristics.
   
4. Brake system contamination and sludging.

Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.

First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry.

Fluid Compatibility

 

Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.

Water absorption and corrosion

 

The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.

Fluid boiling point

 

DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.

DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.

With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.

Brake system contamination

 

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

New developments

 

Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.

[Snarley Bill]

that was a very informative article,thanks for posting it.that pretty well explains it all.i had a 1980 sportster that called for dot 5 brake fluid.i wonder if all harleys do.bill

[Tartan Terror]

that was a very informative article,thanks for posting it.that pretty well explains it all.i had a 1980 sportster that called for dot 5 brake fluid.i wonder if all harleys do.bill

Actually in one of the articles I posted earlier it says they do up to a certain point

 

 

http://www.harleyalaska.com/news_articles_recent.asp

[Guest SALTY]

that was a very informative article,thanks for posting it.that pretty well explains it all.i had a 1980 sportster that called for dot 5 brake fluid.i wonder if all harleys do.bill

 

 

My 98 HD Lowrider took DOT5 but my 06 HD Heritage takes the DOT4

Go figure!

Salty