Synthetic brake fluid question

[TOBASH]

Couple of questions and maybe an answer here.

Please define synthetic. If by synthetic you mean DOT 5, you are bound for failure.

Dot 3 and 4 are essentially the same except DOT4 has a higher boiling point and is hence superior. DOT3 and 4 are meant to ABSORB water, and in this way keep the brakes and clutch alive much as Zinc keeps rust away from steel. I change my DOT 4 every 1 year on my performance cars and every 2 years on things like my Durango. That gets the water out and all the crap and heat damaged fluid and all the grit. Just comparing old to new fluid always reassures me that I am not changing brake fluid too frequently. Old stuff looks like coffee, and new looks like baby oil.

DOT5 synthetic will NOT absorb water. Water will form droplets and those droplets will be free to create rust and destruction. DOT 5 will also "melt" many types of gaskets and seals that are not formulated to work w/ it

Now if you are talking about synthetic DOT3 and 4 I cannot explain your problems away as easily.

Best,

T

 

[rsbcruiser]

Please define synthetic. If by synthetic you mean DOT 5, you are bound for failure.

Dot 3 and 4 are essentially the same except DOT4 has a higher boiling point and is hence superior. DOT3 and 4 are meant to ABSORB water, and in this way keep the brakes and clutch alive much as Zinc keeps rust away from steel. I change my DOT 4 every 1 year on my performance cars and every 2 years on things like my Durango. That gets the water out and all the **** and heat damaged fluid and all the grit. Just comparing old to new fluid always reassures me that I am not changing brake fluid too frequently. Old stuff looks like coffee, and new looks like baby oil.

DOT5 synthetic will NOT absorb water. Water will form droplets and those droplets will be free to create rust and destruction. DOT 5 will also "melt" many types of gaskets and seals that are not formulated to work w/ it

Now if you are talking about synthetic DOT3 and 4 I cannot explain your problems away as easily.

Best,

T

T, I am talking Valvoline synthetic dot 3 -4. It is a synthetic oil based brake fluid. Your explaination, that the old type of dot 3 absorbs water and that water act to condition the rubber seals (if indeed that is what you meant) could actually be the missing book end to the syntho vr dino brake fluid argument. The valvoline syntho claims to absorb less water, possible cause for premature hydro failures.

 

[malcb]

T, I am talking Valvoline synthetic dot 3 -4. It is a synthetic oil based brake fluid.

I thought I had a reasonable handle on brake fluid, now I am not so sure.

I thought;

DOT 3 & DOT 4 were similar and glycol based.

DOT 5 has a silicon base and not compatiable with other fluids but might be OK with standard components?

DOT 5.1 is a high preformance glycol base which is a suitable replacement for DOT 3 & 4.

DOT 5 & 5.1 are called synthetic but in are actually no more "synthetic" than DOT 3 or DOT 4 - it's just marketing and, I see some 3 & 4 brands are now also labeled synthetic - can't though see how they can be different to older DOT 3 & 4 because they are all glycol based.

Apart from DOT 5 being silicon the other exception to the glycol base is mineral oil type (LMH) mostly used by Citroen (and Rolls Royce as they use a system under licence from Citroen).

DOT 3 or DOT 4 are both OK for 40 series, one reason being they absorb more water, although this is sounds bad isn't better than the DOT 5.1 which absorbs less or worse 5 which absorbs almost none. Why? because the water if not absorbed will cause corrosion in the brake system.

DOT 5 is actually a little more compressiable than the others and might have a softer pedal - I am guessing but in a modern ABS vehicle with brake assist etc this might not be an issue - on our old systems it seems to be.

Any big mistakes in the synopsis?

 

[rsbcruiser]

malcb, I learned something today. Went out to the garage, read the brake fluid can, scratched the part sticking out above the carhartts. You Sir, are correct. Dot 3 brake fluid is indeed a glycol based product. here it gets confusing. Valvoline synthetic dot 3-4 brake fluid is also glycol based! I would like to thank you for bringing this to my attention, malcb, you Sir, are a gentleman.

 

[Fast Eddy]

Any big mistakes in the synopsis?

Yup.

I thought I had a reasonable handle on brake fluid, now I am not so sure.

I thought;

DOT 3 & DOT 4 were similar and glycol based.

DOT 5 has a silicon base and not compatiable with other fluids but might be OK with standard components?

DOT 5.1 is a high preformance glycol base which is a suitable replacement for DOT 3 & 4.

DOT 5 & 5.1 are called synthetic but in are actually no more "synthetic" than DOT 3 or DOT 4 - it's just marketing and, I see some 3 & 4 brands are now also labeled synthetic - can't though see how they can be different to older DOT 3 & 4 because they are all glycol based.

The DOT standards simply specify the boiling point of the fluid. For a long time the only fluid that could meet DOT 5 was synthetic silicon-based fluid. Apparently, that has changed. There s a chart of boiling points of the various standards here: DOT 3 - Wikipedia, the free encyclopedia

DOT 3 or DOT 4 are both OK for 40 series, one reason being they absorb more water, although this is sounds bad isn't better than the DOT 5.1 which absorbs less or worse 5 which absorbs almost none. Why? because the water if not absorbed will cause corrosion in the brake system.

This is exactly wrong. Glycol-based fluids absorb water from the air, since the brake system is not completely sealed. The reservoir has a breather. This water then causes corrosion. Silicone-based fluids do not absorb water and will remain clear for easily 10 years.

DOT 5 is actually a little more compressiable than the others and might have a softer pedal - I am guessing but in a modern ABS vehicle with brake assist etc this might not be an issue - on our old systems it seems to be.

Fluid is not compressible. Not ever a little. A "modern ABS vehicle with brake assist" has exactly the same parts as a 40 yo disk brake vehicle and behaves exactly the same until the assist or ABS is activated by it's controller.

My rig has DOT 5 silicone-based fluid in it and it is the same as DOT 3/4, only cleaner. It's been in there for two years, and it looks exactly like the day I put it in there.

 

[Cruiserdrew]

Fast Eddy-I don't think you are correct about this. DOT5 is not compatable and should not be used in these systems. DOT 5.1 would be ok but is unusual.

For Land Cruisers DOT 3 is appropriate and DOT 4 is also good with a higher boiling point.

A ggod plan would be to use DOT 3 and flush every 2 years.

Read this, it's pretty good: Brake fluid - Wikipedia, the free encyclopedia

 

[Fast Eddy]

Fast Eddy-I don't think you are correct about this. DOT5 is not compatable and should not be used in these systems. DOT 5.1 would be ok but is unusual.

"not compatible" based on what? There are all kinds of rumors, but I had DOT 5 in my '69 corvette and now in my '78 cruiser. It works fine. If you don't want to use it, don't, but don't make stuff up.

If you google for "DOT brake fluid", this comes up before the wikipedia article: Tech Tip: Brake fluid debate

For Land Cruisers DOT 3 is appropriate and DOT 4 is also good with a higher boiling point. A ggod plan would be to use DOT 3 and flush every 2 years.

No argument with that. I'd go with DOT 4.

Read this, it's pretty good: Brake fluid - Wikipedia, the free encyclopedia

This article does not cite any references or sources. (June 2008)
Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.
This article may require cleanup to meet Wikipedia's quality standards

Pretty standard misinformation there too.

 

[FJROSS]

I myself have been running the dot 5 for about 8 years in my Cobra now with no problems. The one thing that I was told was that a system must be flushed entirely and all the rubber hoses and seals switched out before changing over to the silicon based fluid. The dot 3 and 5 are not compatible with each other. I'm wondering if this could be the reason that some people are not happy with the results after switching over. From what I understand the seals become soft after being contaminated and may not push fluid like they should. Silicon is used often in muscle and classic car restoration due to the fact that its not harmful to the paint and the fact that it doesn't absorb water. This is a good option for vehicles that are not used as often as daily or weekend drivers.

Dave

 

[Cruiserdrew]

There are two issues to be concerned with. Since the fluids are completely incompatible, all traces of the old stuff has to be removed before puttting in the new stuff. Unless you are replacing the hydraulic cylinders and blowing out the open lines, I don't see how you could preclean the system well enough. I tried this once with a motorcycle and after much frustration, had to switch back.

The other issue is that absorbing water is actually a benificial property of the DOT3/4 fluids. That way the water that does find it's way into the system is scavenged by the fluid and not available to cause problems in the system. With DOT 5 that does not happen, and any water that gets into the system exists as droplets and will promote rust and corrosion. In a mass market situation where neglect is a major issue the hydroscopic fluid wins. If DOT 5 were better, the car companies would likely use it.

There probably are situations where DOT 5 has desirable properties-like the over anal constantly renewed and flushed systems of "serious car collectors", where cars live inside under a cover and get driven once a month on sunny days. The lack of risk to paint would be a major advantage and worth completely flushing out the system to run this fluid. For a Land Cruiser used in real world conditions, where parking outside, water and grime are part of the expected program, I don't see the advantage to DOT 5, but then maybe I missed something.

 

[F-junker]

Oh my, why ask why??
I too would really like to know; is it the micro bubbles in that stuff that make bleeding impossible or is it just s***e'. I gave up, and went to the stuff I'd been using all my life and sad forgetaboutit. Silicon fluids are good for cars not driven very often and needing less maintenance. I had it in a big block vette and found it to be useful in every way but performance. Keep in mind I don't have the power to weight ratio of a Cobra! Yes if you use it you do have to flush everything out. I switched back to dino dot 3 using a german brand and flushed it with several quarts of brake fluid. you can see that the two do NOT mix as it comes out of the bleeder tube.

 

[Fast Eddy]

There are two issues to be concerned with. Since the fluids are completely incompatible, all traces of the old stuff has to be removed before puttting in the new stuff. Unless you are replacing the hydraulic cylinders and blowing out the open lines, I don't see how you could preclean the system well enough.

I started with all-new OEM parts (master, wheel cylinders, calipers, flex lines) when I switched. It was about $700, I think. I didn't do anything special with the hard lines other than a standard, thorough bleeding.

 

[malcb]

Yup.

Or maybe I wasn't so far off the mark?

This is exactly wrong. Glycol-based fluids absorb water from the air, since the brake system is not completely sealed. The reservoir has a breather. This water then causes corrosion. Silicone-based fluids do not absorb water and will remain clear for easily 10 years.

Provided no water is present already or gets in during the ten years. If it is there or gets in it will be free, not bound into the fluid and will settle in low point ansdcause corrosion - been puzzleing how does it get in, I can imagine hydroscopic DOT3, 4 or 5.1 absorbing water in top of the the reservoir, water or condenstion in the cylinders working past the seals? that could affect DOT5 silicone as well as normal stuff.

From http://www.millersoils.net/1_downloads/literature/motorsport/M-tt_BRAKE_FLUID.pdf​

Silicone Brake Fluid (DOT 5)
Silicone based DOT 5 was originally introduced to give higher temperature performance over glycol
DOT 4. Silicone fluid also has other advantages, it does not damage paintwork and it does not absorb
water. However, silicone fluid is a poor lubricant and does not lubricate ABS pumps as well as PAG fluids.
It is also more compressible than PAG fluids, which can result in a sluggish or spongy pedal. It therefore
requires special design considerations in baking systems. Further, because it does not absorb water, any
water remains as globules, which can pool in low spots in the system and cause corrosion. This water can
vaporise when heated under heavy braking giving a disastrous effect on braking efficiency.​

DOT5 fluids are not recommended for motor sport applications

Fluid is not compressible. Not ever a little.

Fluid is closely spaced molecules rather than the widely spaced molecules in a gas but it can still be compressed, as can solids to some extent, but yes neither is "very" compressiable.

It seems though that that the issue with silicon based brake fluids in the molecular make up actually allows air to be retained in a suspension, other sources on the net suggest that silicone based brake fluids can have siginificant mounts of disolved air contained in the fluid which at high temps can have adverse affects. I don't see the latter being an issue on a LC with drums but with the large volumes and displacements in our systems perhaps the first is what leads to people finding a different feel with silicone bases fluids?

From this site StopTech : Balanced Brake Upgrades
So why is silicone-based DOT 5 fluid more compressible than other fluids?

On their own, silicone-based DOT 5 fluids are entirely different animals than DOT 3 and DOT 4 fluids. In addition to having characteristically higher dry and wet boiling points, they also tend to have much, much lower viscosities. In other words, they flow more easily relative to temperature.
One side effect of this chemistry is that there is more “room” for air to fit in-between the individual molecules of brake fluid than in DOT 3 or DOT 4 fluids. Note that we are not talking about big bubbles of air here which are visible to the naked eye, but rather microscopic amounts of air which are finely dispersed (entrained) in the brake fluid matrix.
Now, all fluids have a certain amount of compressibility to start with, but adding even the smallest amount of air into the solution can dramatically increase the amount of elasticity in the system. In the case of silicone-based fluids, air is quite happy to take up residence between the brake fluid molecules, and as a result the fluid compressibility goes down. This is felt at your foot like stepping on a big spring. As you can imagine, more air = more spring.

And this one Brake Fluid Explained QuadrigaMotorSports.com™

Air Solubility - It has been reported that dimethyl polysiloxane fluid, which is a major component of silicon based low water tolerant type brake fluids (SAE J1705), can typically contain dissolved air at a level of 16% ± 3% by volume at standard temperature and pressure. This compares with a typical level of 5% ± 2% by volume of dissolved air for glycol ether based SAE J1703 type fluids. An increase in brake pedal travel may be experienced under severe operating conditions, especially at higher altitudes and high temperature conditions.
The term “dissolved air” (air absorbed from the atmosphere) should not be confused with the term “entrapped” or “free air” since their effects on brake system performance can be entirely different. Air that has been absorbed from the atmosphere does not result in an increase in fluid or system volume, whereas entrapped air or free air does occupy system volume and can be easily compressed when force is applied to the system. 5

A "modern ABS vehicle with brake assist" has exactly the same parts as a 40 yo disk brake vehicle and behaves exactly the same until the assist or ABS is activated by it's controller.

Ha Ha - I can't disagree the parts are similar, I know what point your trying to make but a there are differences - perhaps the boosters have more mechanical advantage, the pipes are smaller, the flexiables less expandable , the calipers more efficent...... no 40 year old system will match a 2008 brake system that just has the ABS fuse pulled. See extract above from Miller Oils.

My interest is mostly because DOT3 is rare in the UK and DOT4 is the norm but DOT5.1 seems to be overtaking DOT4 on the shelves. Everything suggest DOT4 is OK for me and thats what I think I am going to use but I still don't know if there is any specific difference or compatability issues between DOT4 old style and DOT4 synthetic or would I be better with DOT5.1?

 

[leadvagas]

Boy, I really shouldn't do this but........I will anyway. The fact that DOT3 & 4 are hygroscopic in no way represents a good thing. The water changes boiling points and the specific proporties of the fluid. DOT3/4 fluids do NOT sequestor water and keep it from causing corroding compenents. It just makes a water contaminated mix with a low Ph, about 5.5 or so when loaded with more than about 15% water. Thats why aircraft don't use Glycol based hyrauilic fluids. In enviroments where temperatures swing over relativley mild ranges and relativley low humidity, then DOT 3&4 will likley last a good couple of years. Increase either humidity levels or broad temperature swings and you get less life. If you really want the ultimate in brake fluids switch to something like MIL-H 5606, first you MUST verify that there are NO natural rubber compenents in the system. I doubt that there are new natural rubber components out there, 99.9% of all seal compenents made in the last 30 to 40 years are Viton or Buna N. and are compatable w/most any modern fluids inclueding Silicone. In the final analysis, using any DOT fluid will be fine as long as you do the set-up and maintenance as per manufacturers directives. If you are getting degridation of components with any fluids, you've got contamination issues at least.

 

[rsbcruiser]

[quote=leadvagas; Boy, I really shouldn't do this but........



What the hell leadvegas? You should and did. your comments are not only informative but.......wanted. You plugged a hole in this debate for me. The rubber thing, that is exactly what I was wondering about. The others though, they have good arguments pertaining to water reactions. I notice you say that it does not sequester water. Ok that is fine but what about the argument that glyco fluids absorb water, therefore the water goes into suspension and does not seperate. And the microbubbles argument. I have special interest in this subject because I vacuum bleed. You mention the mil-spec brake fluid, can we the humble civilian scourge get any? Where? What is it? And consider this. Older brake systems were designed to work the higher viscosity older fluids. might make zippo diff but. Anyways, if you are packing info like that you are more than welcome on this playground.

 

[malcb]

I knew absorbing water reduced the boiling point but the dry vrs wet figures and the water in low points vrs water absorbed into the fluid made sense untill you said PH value.

Slightly disturbing that both arguments for every point on the thread are avaliable on the web, often from quite reliable looking sources.

(I like wiki but am frustrated by the fact the author could be anyone and the facts are not often adequately referenced)

 

[Fast Eddy]

Or maybe I wasn't so far off the mark?

Fluid is closely spaced molecules rather than the widely spaced molecules in a gas but it can still be compressed, as can solids to some extent, but yes neither is "very" compressiable.

I'll say it again, fluid is not compressible. Otherwise you could fit two liters in a one liter container.

Anyone who thinks that DOT 5, by itself, at room temperature can cause a spongy feel is an idiot.

If you dump some into an old system with whatever DOT 3 and some water and maybe some solvent to clean it out and some old seals, and then it's spongy, maybe. Those folks then wrote their experiences on the internet and they end up as the result of a google search. Just cause you read it on internet doesn't mean it's true.

I have DOT 5 in my brake system and it is not spongy. It works perfectly and it's clear as the day I put it in there, as it will be in another 5 years.

 

[malcb]

I'll say it again, fluid is not compressible. Otherwise you could fit two liters in a one liter container.

Anyone who thinks that DOT 5, by itself, at room temperature can cause a spongy feel is an idiot.

If you dump some into an old system with whatever DOT 3 and some water and maybe some solvent to clean it out and some old seals, and then it's spongy, maybe. Those folks then wrote their experiences on the internet and they end up as the result of a google search. Just cause you read it on internet doesn't mean it's true.

I have DOT 5 in my brake system and it is not spongy. It works perfectly and it's clear as the day I put it in there, as it will be in another 5 years.

Well I never thought I would ever read as much about brake fluid. I hope I am not an idiot - the suggestion was the spongy pedal if it is a function of the DOT5 was because bleeding didn't get all the air out.

My conclusion in I am happy to use DOT4, if were going to reuild the whole system with new parts etc I would consider DOT5 silicone on the basis of it not absorbing water. (DOT5.1 should be an irrelavant to drum brakes on there vehicle - if it gets that hot in there your in trouble)

Air bubbles and bleeding seem to be a distraction, I belive with care and perhaps a second bleeding that is not an issue and the spongy pedal with cold brakes should be avoidable.

Sorry to say it but the downside to DOT5 /silicone is still the compressability. The site below is related to Triumph cars but has some interesting calculations on the extra pedal movement with silicon. The authors conclusion is DOT5 is his perfered fluid but I wonder what the figures would be for a LC system, given he has disk fronts and drum rears with 0.7" cylinders, as I said before lots of fluid displacement in our systems. Note this is not spongy pedal but extra travel.

Selecting Brake Fluid


Also on the site some figures on absorption of water that answered a question for me - won't water get into a silicon filled system the same as a glycol base system - seems it won't.

Anyway thats me done.

 

[rsbcruiser]

I'll say it again, fluid is not compressible. Otherwise you could fit two liters in a one liter container.


Not so fast, Eddy. Did you think I was going to leave that one alone? Apparently you were paying attention that day in High School Science, you should have skipped that day. Confusion on this subject is quite common because of a definition. A liquid is defined as an incompessible fluid. It is a definition not a reality. Picture the line to your back brakes as a 10 foot column of liquid. With that in mind (defy the laws of Physics?) how could you say there is no compression. As malcb pointed out, you can even measure it! What you said makes about as much sense to me as saying your springs don't flex. Damn' it malcb, I was about to whip out my BSME and beat him with it. Ah well, suppose you are right, emotional responses don't yield logical arguments, dang, dang, dang. Lets not lose perspective, there it is, emperical evidence that at least one guy has operated a silicone system for five years without a problem.

 

[rsbcruiser]

Well, that was interesting. I switched from the Valvoline synthetic dot 3-4 sylicone based brake fluid to a dot 3 old school brake fluid in my brake system. Problems started developing soon after. My brake pedal would not return fully. I think I found the problem. This is a picture of one of my front brake cylinders. Guess I won't be doing that again. going back to the syntho again after i fix this.

 

[Fast Eddy]

Rust?