upgrading the OEM master cylinder?

[Mike Cecchini]

One of the best things about the DOT 3/4 stuff . . . . he'll know when it goes bad . . . . the color changes - Drastically. It absorbs and mixes with the moisture, and that changes it's color

My 1994 Miata still has it's original brake fluid - 60,000 miles. The clutch fluid has had to be changed 3 or 4 times and both the clutch master and the clutch slave too. I credit the difference (between the fluid life in the clutch and the brakes) to the fact that the clutch master has a small air vent hole in the cap, which allows ambient air to be drawn into it with each push of the pedal . . . . because it's vented, the clutch fluid changes color about every 4 or 5 years . . . . the brake fluid on the other hand still looks like it did when the car was new. The brake master has a huge, unvented rubber bellows atop the fluid so it doesn't draw in any air

There advantages and disadvantages to everything - Like anything else, you pick the one you like the best and dislike the least and go with that. For me, that's always been the 'regular stuff'

Don

If it's original fluid in Ricks 1947 and 1949 trucks......it's probably something much less than DOT 3 or 4. I Googled when DOT 3 came into use, but couldn't find any dates........but I dare say that after 60+ years Rick's trucks brake fluid is quite bad. God only knows how and why the trucks brakes work at all for they should have seized up decades ago.

Yes, brake systems need to be vented, but they are sealed against the atmosphere via a rubber bellows that sits right under the cap on every master cylinder.

I agree with you Don....... there are advantages to everything it seems, but for our X's that sit and sit for months and sometimes years, unless you change-out the brake fluid every 2--3 yrs, then internal master cylinder and caliper corrosion will develop especially if the bikes are kept in a un-controlled environment. Even my X's that are kept in a/c and heated garage corroded in 4 yrs.

Frankly, I'm beginning to think that the lack of use plus no change-outs lets things corrode quicker than if the bike is used so things get moved in the brake system.

So you haven't changed your Miata's brake fluid in 17 years ? Wow

Maybe someone put DOT 5 in it.

My best.

[Mike Cecchini]

One of the best things about the DOT 3/4 stuff . . . . he'll know when it goes bad . . . . the color changes - Drastically. It absorbs and mixes with the moisture, and that changes it's color

My 1994 Miata still has it's original brake fluid - 60,000 miles. The clutch fluid has had to be changed 3 or 4 times and both the clutch master and the clutch slave too. I credit the difference (between the fluid life in the clutch and the brakes) to the fact that the clutch master has a small air vent hole in the cap, which allows ambient air to be drawn into it with each push of the pedal . . . . because it's vented, the clutch fluid changes color about every 4 or 5 years . . . . the brake fluid on the other hand still looks like it did when the car was new. The brake master has a huge, unvented rubber bellows atop the fluid so it doesn't draw in any air

There advantages and disadvantages to everything - Like anything else, you pick the one you like the best and dislike the least and go with that. For me, that's always been the 'regular stuff'

Don

Too funny........ if the brake fluid in Ricks 1940's trucks is original as Rick says it is........and it hasn't changed color after 60+ years, I dare say it's never going to change color. I suspect that it's a brake fluid that's not designed to change color as DOT 3/4 is. Regardless, I'm amazed both trucks brakes aren't locked up solid.

All in all Don, for our X's that sit around year after year with little or no use......DOT 5 is the way go for so many real world reasons. No damages to paint or plastic if spilled......which is so easy to do.....especially if the lever is pumped too variously while attempting to pump-up the lever during bleeding. Long change-out intervals (2 yrs vs 5+ yrs) and DOT 5 silicone doesn't absorb water like DOT 3/4 does so aggressively.

Btw....I'm really surprised you haven't changed out the 17 yr. old brake fluid in your Miata

Maybe someone put DOT 5 in it long ago........

My best.

[EMS]

Please, Mike, make another post just like it . Just change two or three words. Maybe then, we will all run out and buy DOT5 and change our brake fluid immediately.

[Mike Cecchini]

Ok Mike....... I'll give it another go. ;))

[Don]

All in all Don, for our X's that sit around year after year with little or no use......DOT 5 is the way go for so many real world reasons. . . . . DOT 5 silicone doesn't absorb water like DOT 3/4 does so aggressively.

You're right, Mike, it doesn't - That's one of it's biggest disadvantages as Mike Nixon so clearly pointed out

Here's the facts for you Mike: "Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance."

Brake fluid which *does*mix with water is better because 1.) The water is much less corrosive when mixed in with glycol brake fluid than straight water alone. 2.) Glycol brake fluid is heavier than water, so the water doesn't eventually work it's way to the bottom of the closed system. 3.) When there is water in glycol fluid, you have ample warning due to the color change

All brake systems get water in them Mike, and for the same reason, regardless of the fluid used and at about the same rate - You just can't see yours

Therefore, Mike Nixon tells us that when you choose to use silicone fluid you must change it *more frequently* than if you use glycol based fluid - His facts and rationale are good enough for me

Now . . . . you get the last word Mike, 'cause there's no point in arguing with you. The facts are knocking knots on your head and you don't feel a thing

Don

[Mike Cecchini]

All in all Don, for our X's that sit around year after year with little or no use......DOT 5 is the way go for so many real world reasons. . . . . DOT 5 silicone doesn't absorb water like DOT 3/4 does so aggressively.

You're right, Mike, it doesn't - That's one of it's biggest disadvantages as Mike Nixon so clearly pointed out

Here's the facts for you Mike: "Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. <snip>

Brake fluid which *does*mix with water is better...... because 1.) The water is much less corrosive when mixed in with glycol brake fluid than straight water alone. 2.) Glycol brake fluid is heavier than water, so the water doesn't eventually work it's way to the bottom of the closed system. 3.) When there is water in glycol fluid, you have ample warning due to the color change

<snip>

Therefore, Mike Nixon tells us that when you choose to use silicone fluid you must change it *more frequently* than if you use glycol based fluid - His facts and rationale are good enough for me

Now . . . . you get the last word Mike, 'cause there's no point in arguing with you. The facts are knocking knots on your head and you don't feel a thing

Don

Hi Don,

Good to hear from you again.

Re: Silicone DOT 5 doesn't absorb water at all vs DOT 3/4 absorbs water/humidity aggressively. Tis true..... but you (and may others) draw the wrong conclusions from this fact.

1. When a brake system filled with DOT 4 is opened for any reason, not only does it aggressively absorbs any moisture from the surrounding air, but it also readily and aggressively absorbs moisture from the air that is changed-out at the master cylinder as the m/c top is removed and put back on. DOT 5 doesn't do this aggressive moisture absorption. To make the point clear, for instance, on a scale of 1--100, DOT 4 is a 90 and DOT 5 is a 1.

2. DOT 4 continues it's aggressive moisture absorbing at any opportunity such as leaks, because not only is the DOT 4 leaking out..... there is moisture being absorbed by the DOT through the leak. DOT 5 does not allow this to occur because it is a fluid shield that does not absorb moisture and in this circumstance it repels the admittance of moisture into the brake system.

Re: Brake fluid which does mix with water is better......

1. I disagree with this premise. DOT 4 mixes with water and this water spreads through-out the entire brake system thereby exposing the entire brake system to corrosive brake fluid/ water mix. If and when any moisture is allowed to enter a DOT 5 system (already at a extremely lower amount than DOT 4)...... the water does not mix with the DOT 5 and therefore the rest of the brake system is not exposed to this miniscule amount of moisture. Therefore, the rest of a DOT 5 brake system is not exposed to moisture.....so the rest of the brake system does not corrode like a DOT 4 brake system will do....everywhere.

Bottom line..... DOT 4 brake systems absorb, hold and spread the corrosive properties of moisture. This is why auto and bike makers tell us to change-out DOT 4 brake fluid every 2 years. On the other hand DOT 5's change-out recommendation is in the 5 to 10 year range.

See ?? All common sense once you look at the facts and change-out recommendations. I'm really surprised Mr. Nixon hasn't picked up on all this......but then everyone makes a mistake now and then.

Btw Don.... this isn't an argument..... it's a discussion...... and it's been good discussing things with you.

My best........Mike

[Larry Zimmer]

Significant issue with the DOT 5 not mixing with water is that the water migrates/settles to the bottom, being heavier than the silicon fluid. That means that any moisture that gets into the system will eventually settle to the pistons in the calipers. From there it will lead to corrosion over time (if not changed very regularly); and, with hard enough braking, 'steam' in the calipers due to heat transfer from the pads/pistons. That's where the spongy brake feel and lost effectiveness develops. In racing applications where fluid changes can be regular, not a problem. The DOT 5 high temperature properties are a benefit to racing.

Note that DOT 5.1 is an entirely different fluid. It works similar to DOT 3 & 4. No problem.

[EMS]

Larry:

For quite some time, until 2009, I was involved in a race team competing in Grand Am Road Racing. We were using Motul RBF brake fluid. I was digging through my stuff and found this memo from the fluid supplier:

Fluid Fact.

Due to the extreme operating temperatures of a high performance brake system, standard 'off-the-shelf' brake fluids are not recommended. Of critical importance in determining a fluids ability to handle high temperature applications is the Dry Boiling Point and compressibility.
The Dry Boiling Point is the temperature at which a brake fluid will boil in its virgin non-contaminated state. The highest temperature Dry Boiling Point available in a DOT 3 fluid is 572 F

The Wet Boiling Point is the temperature a brake fluid will boil after it has been fully saturated with moisture. The DOT 3 requirement for wet boiling point is a minimum temperature of 284 F.

There are many ways for moisture to enter your brake system. Condensation from regular use, washing the vehicle and humidity are the most common, with little hope of prevention. Glycol based DOT 3 & 4 & 5.1 fluids are hygroscopic; they absorb brake system moisture, and over time the boiling point is gradually reduced.

We do not recommend using DOT 5 fluid in any racing applications. DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers . It is not uncommon to have caliper temperatures exceed 200 F, and at 212 F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel. DOT 5 fluid is best suited for show car applications where its anti-corrosion and paint friendly characteristics are important.

[Don]

That's pretty much the same as everything else I've read on the subject Mike. Moisture contaminated glycol based fluid is much preferable (both from the boiling point and the corrosion factor) than the pure, unmixed water in a closed system with silicone fluid - If the silicone was heavier than water, so the water rose to the top (away from where the heat is generated) it might be another matter

But, the single biggest factor of one over the other for me is the color change you get when moisture mixes with the glycol stuff - You know to change it then. With the silicone stuff, you just assume everything's OK until you experience the inevitable failure

Don

[Larry Zimmer]

Thanks for all the good info, Mike. It, certainly, should help all our members answer any question relative to proper brake fluid application. Appreciate your digging.

[Rick Pope]

So, if you have a bunch of vehicles that never get used much, ridden in the rain, or even gotten dirty to require washing, DOT 5 might work.

For normal people, stick w/ DOT 3/4.

[EMS]

So, if you have a bunch of vehicles that never get used much, ridden in the rain, or even gotten dirty to require washing, DOT 5 might work.

For normal people, stick w/ DOT 3/4.

Exactly! I am thinking of putting an "upstairs" in my garage to store some of my (currently) 16 bikes, which I never get to ride. They may get DOT5.

[Mike Cecchini]

Significant issue with the DOT 5 not mixing with water is that the water migrates/settles to the bottom, being heavier than the silicon fluid. That means that any moisture that gets into the system will eventually settle to the pistons in the calipers. From there it will lead to corrosion over time (if not changed very regularly); and, with hard enough braking, 'steam' in the calipers due to heat transfer from the pads/pistons. That's where the spongy brake feel and lost effectiveness develops. In racing applications where fluid changes can be regular, not a problem. The DOT 5 high temperature properties are a benefit to racing.

Note that DOT 5.1 is an entirely different fluid. It works similar to DOT 3 & 4. No problem.

Kinda yes and kinda no Larry...... the amounts of water that migrate into a DOT 5 system is so small (especially compared to DOT 4 fluids which aggressively absorb moisture vs DOT 5 which repels it) that all the car and bike companies that use DOT 5 recommend change-out of DOT 5 in the 5--10 yr range vs 2 yrs for DOT 4. After 20+ yrs of using DOT 5 I've yet to find corrosion or any indication of moisture in my brake systems.


Also, DOT 5 has been found inferior to DOT 4 in racing applications.....not because of DOT 5's higher temperature rating.....but because in racing situations brakes can go above DOT 5's range where it looses it's piston to cylinder wall lubricating abilities. With DOT 4 if you exceed it's temperature range you boil the fluid but the piston to cylinder wall lubrication remains. I found this out when I asked some F1 mechanics at Watkins Glen just after DOT 5 was introduced and they told me that DOT 5 didn't work and to use DOT 4 in racing.

[Mike Cecchini]

So, if you have a bunch of vehicles that never get used much, ridden in the rain, or even gotten dirty to require washing, DOT 5 might work.

For normal people, stick w/ DOT 3/4.

If you like to change out brake fluid every 2 yrs. all good and well Rick.....but DOT 5 isn't just for bikes that sit around. DOT 5 is for those of us who use our bikes in everyday rides in all kinds of weather. It's such a friendly fluid to painted and plastic parts that one never need worry about getting it on anything because it wipes right off with no harm done.

Personally I've found DOT 5 to be a God-send in so many real world everyday situations that I'll never go back to DOT 4.

My best........ Mike

[Don]

Interestingly, neither GM, Ford or Chrysler have any recommended change interval for their vehicles which came factory equipped with DOT 3/4 fluid. GM says that additives in it's Delco DOT 3 brake fluid make it 'essentially a lifetime product'

Modern brake systems are pretty well sealed. While it's true that the glycol based fluids are hygroscopic and will absorb moisture if left open to the atmosphere, any sealed brake system gets contaminated with moisture at about the same rate, no matter what fluid is used . . . . but a percent or two of water in a glycol system is much less of a concern from either a corrosion or a boiling standpoint than same amount of moisture in a silicone system

It appears we have so many folks here who have had such phenomonal success using all types of brake fluid, that no reader should worry a lick about whatever fluid they're using ;)

Don