REFLECTOR: DOT 5 Compatability

[Ron Brown]

Bob, this is the first time I have heard anything about DOT7. From chapter 8 of the online manuals (page 8-8):

Once the system is all hooked up, add DOT5 brake fluid and bleed the system from the bleeder on top of the brake assembly.   

The top of your brake master cylinders reads dot3. Dot 3 is not compatible with the Matco brakes so it is a good idea at this time to mark the tops of your master cylinder DOT5 to avoid confusion in the future.

And as a precaution, DOT 5.1 is TOTALLY DIFFERENT FROM DOT 5. DO NOT CONFUSE THE TWO!!!

For those of you who want to know all there is to know about brake fluids, read the following excellent write up by Dale Martin, excerpted from the Canard list last week:

Let's start with an first an understanding of the terms and what they mean.. 
Following this is an overview of the different specifications and chemistry 
of brake fluid. 

*Brake Fluid Specifications:*

All brake fluids must meet (comply with) Federal Motor Vehicle Safety 
Standard #116 (FMVSS 116.) Under this standard are three Department of 
Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, 
DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 
5 (for Silicone based fluids). 

*Understanding Brake Fluid Terms:*

*Dry Boiling Point* - Or more accurately termed Equilibrium Reflux Boiling 
Point (ERBP). In fluids deemed to be DOT compliant, this is the temperature 
at which the fluid begins to boil when tested in the manner described by the 
DOT.

*Wet Boiling Point* - Or more accurately termed Wet Equilibrium Reflux 
Boiling Point (Wet ERBP). In fluids deemed to be DOT compliant, this is the 
temperature at which the fluid begins to boil when tested in the manner 
described by the DOT. FWIW, the procedure for this a reference fluid is 
placed in the specified container at the same time as the testing fluid is 
placed in a similar container. When the reference fluid reaches
3.70±0.05%water content by weight, both the reference fluid and the
testing fluid are
removed. The testing fluid is then put through the same procedure as for Dry 
ERBP. That temperature point is noted as the Wet ERBP.

Note, this DOES NOT mean the testing (sample) fluid also had 3.7% water 
content. In fact, depending on the fluid, it may have less or it may even 
have a GREATER percentage of water content.

In reference to the DOT (or SAE) test, a typical Dot 3 fluid will contain 
approximately 3 - 3.5% moisture, a DOT 4 fluid will contain 4-4.5% moisture 
content by volume. However it is possible, although quite a bit more 
expensive, to create a Super DOT 4 fluid, like GS610, where the moisture 
content is closer (lower) to that of DOT 3 but still has a much greater 
tolerance for moisture. This means that even when the fluid has become 
contaminated with a greater percentage of water content, for example, 4.5 - 
6% by weight, it continues to maintain is Wet ERBP performance and not 
degrade further. 

*Viscosity* - Here's a really interesting specification. One where the DOT 3 
spec could be perceived as actually being better for the micro passages of 
an ABS system than the DOT 4 spec. Webster's defines "viscosity" as, 
"Physics, the resistance of a fluid to flowing freely, caused by friction of 
its molecules." As you may recall from motor oil, the higher the viscosity 
number, the slower the flow of the oil. Well the same applies for brake 
fluid although the actual measurement technique is different. The DOT 3 
specification for viscosity at -40°F is 1500 mm2/s and the specification for 
DOT 4 at -40°F is 1800 mm2/s. Yep, that's right, the DOT 3 fluid flows 
better at the testing temperature than the DOT 4. It should be noted the 
specification at 212°F for all DOT specifications is 1.5 mm2/s. 

*Compressibility* - This is NOT a specific DOT specification however it 
listed in SAE J1705, Appendix A, A.2.2.8. under the heading, "Air 
Solubility." Here it states, "Air Solubility - It has been reported that 
dimethyl polysiloxane fluid, which is a major part of silicone based low 
water tolerant type brake fluids 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 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."

The SAE standard continues, "A.2.2.9 - Compressibility - Silicone based 
brake fluids are more compressible than conventional brake fluids and the 
difference is magnified at higher temperatures."

Compressibility is something you'll find most, if not all other brake fluid 
brands completely ignoring. And with good reason! They don't want you to 
know their fluid could or does contain as much as 7% dissolved air! No 
wonder certain "high end racing" fluids are known for their poor pedal feel.

Polyalkylene Glycol Ether type brake fluids are over 3 times less 
compressible than silicone (low water tolerant) type fluids, even when 
heated. And even within the scope of the Polyalkylene Glycol Ether fluids, 
there can be a difference of over 200% between a fluid like GS610 with 
minimal dissolved air and other fluids containing far more!

A research report from Union Carbide demonstrates a relationship between the 
compressibility of a brake fluid and its density (specific gravity.) The 
greater the density of a brake fluid the less compressible it is. GS610 is 
the most dense brake fluid on the market today!

*pH* - This is another DOT specification The range of pH to meet FMVSS 116 
is 7 -11.5. pH is an indicator of a couple of important issues. One is the 
fluid's corrosion resistance and the other is it's high temperature 
stability. A higher pH will prevent corrosion for a longer time however 
higher pH values also reduce the fluid's high temperature stability. If the 
pH is below 7, the system is on the acidic side and may produce corrosion 
within the system over time. Certainly if it is below 6 problems will occur. 
Steel does not corrode as long as the pH is above 9.5 but aluminum will be 
attacked if the pH goes above 11.5. A ph lower in the range will provide all 
the corrosion protection you need while maintaining maximum high temperature 
stability.

*High Temperature Stability* - This is a measure of how stable the dry ERBP 
temperature is as fluid temperature increases. And it applies universally to 
all grades of brake fluids. The specification per FMVSS 166 reads, ".. The 
ERBP shall not change by more than 5.4°F (3°C) plus 0.05 for each degree the 
ERBP of the fluid exceeds 437°F (225°C.)" For a fluid with the extreme ERBP 
of GS610 the ERBP could vary in either direction by as much as 14.05°F (
9.97°C). That said, please note the High Temperature Stability of GS610 is 
actually 2°F (1°C)

*Brake Fluid Descriptions:*

*DOT 3:* This brake fluid has a glycol base with additives. It is clear to 
amber in color. It is hygroscopic (meaning it absorbs moisture) and has a 
minimum dry boiling point of 401°F (205°C) minimum and a minimum wet boiling 
point of 284°F (140°C). It will absorb 1 to 2 percent of water per year 
depending on climate and operating conditions. It is used in most domestic 
cars and light trucks in normal driving. It does not require cleaning the 
system and it can be mixed with DOT 4 and DOT 5.1 without damage to the 
system. The problem with it is that it absorbs moisture out of the air and 
thereby reduces its boiling point. It can also damage the paint on a 
vehicle. 

*DOT 4:* This brake fluid also has a glycol in it but the SAE J1704 
specification considers it to be a borate ester base fluid. Typically in the 
high performance fluids, it also contains other additives. It is clear to 
amber in color. It is hygroscopic (meaning it absorbs moisture) and has a 
minimum dry boiling point is 446°F (230°C) and minimum wet boiling point of 
311°F (155°C). It is used in many European cars; also for vehicles in 
high-altitude, towing, or high-speed braking situations, or ABS systems. It 
does not require cleaning the system and it can be mixed with DOT 3 without 
damage to the system. The problem with it is that it absorbs moisture out of 
the air and thereby reducing its boiling point, however it absorbs moisture 
at a rate slower than DOT 3. It can also damage the paint on a vehicle. 

*DOT 5:* This brake fluid has a silicone base. It is purple in color. It is 
NOT hygroscopic (meaning it cannot and will not moisture) and has a minimum 
dry boiling point of 500°F (260°C) and a minimum wet boiling point of 356° 
(180°C) It is not used in many brake applications, seeing primary duty in 
weekend, antique, and collector cars that sit for long periods and are never 
driven far. It does not mix with DOT 3, DOT 4, or DOT 5.1. It will not 
absorb water and will not damage the paint on a vehicle. It is also 
compatible with the same rubber formulations as the DOT 3, 4 & 5.1 fluids. 
The problem with it is that it can easily get air bubbles into the system. 
The air bubbles are nearly impossible to remove and result in poor system 
performance and poor pedal feel. Although originally developed in the late 
1960's by General Electric specifically for racing, it is unsuitable for 
racing for a variety of reasons. (Scroll to the bottom for the scoop on 
Silicone) If as little as one drop of water enters the fluid, severe 
localized corrosion, freezing, or vapor lock may occur. This can happen 
because water is heavier and not mixable with silicone fluids. It is 
unsuitable for ABS. 

*DOT 5.1:* This brake fluid is similar to DOT 4 it has a base comprised 
primarily of Borate Ester. Often in the range of 70 - 80%. To meet 
specification, it also will contain other additives. It is clear to amber in 
color. It is hygroscopic (meaning it absorbs moisture) and has a minimum dry 
boiling point of 500°F (260°C) and a minimum wet boiling point of 356°F 
(180°C) minimum. It is almost exclusive to Europe, used in high performance 
cars. It can be mixed with DOT 3 or DOT 4 without damage to the system. It 
maintains higher boiling point than DOT 3 or DOT 4 fluids due to its even 
greater borate ester content. It is excellent for severe duty and racing 
applications. The problem with it is that it costs more than other fluids 
and there is limited availability in the USA. It also absorbs moisture out 
of the air and thereby reduces its boiling point. It can also damage the 
paint on a vehicle. 

*Fluid Compatibility*
Brake fluid must be compatible with the brake system materials. 
Compatibility is determined by chemistry, and no amount of advertising, 
wishful thinking or rationalizing can change the science of chemical 
compatibility. DOT 3, 4, 5 and 5.1 fluids must, to meet the specification of 
Federal Motor Vehicle Safety Standard 116 (FMVSS 116) be compatible with all 
specified brake system materials except in the case of DOT 5 silicone. Some 
rubber external components such as caliper piston boots, may be attacked by 
silicon fluids and greases.

*Water Absorption and Corrosion*
What most don't understand is some degree of water absorption is desirable. 
DOT 3-4-5.1 glycol based fluids will readily absorb water. Like many other 
things, this is a good thing (to a degree) as your brake system does contain 
water and there is nothing you can do about it. However there are corrosion 
inhibitors in the brake fluid formulation that handle this. Since the 
inhibitors are gradually depleted as they do their job, glycol brake fluid, 
just like antifreeze, needs to be changed periodically. The one caveat to 
this is the DOT 5 silicone 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
3-4-5.1fluids, and will remain as a separate globule sinking to the
lowest point in
the brake system (typically the caliper), as water is more dense. The other 
issue with this is now you have water coming in contact with the metal 
components of the brake system. This can actually exacerbate the corrosion 
issue.

*How fast does brake fluid absorb moisture?*

It depends on the fluid and environment. A typical high performance DOT 4 
fluid like, Motul, AP, Castrol SRF, Wilwood and ATE SuperBlue, in a high 
humdity evironment will absorb as much as 4.5-5% moisture in as short a 
period as 2 weeks. In real world testing (several daily driver cars, GS610 
absorbed <1% moisture in 3 years. This was measured from the brake fluid in 
the resevoir where the vehicle's brake system is most likly to contain the 
greatest contaimination of moisture.

*How does brake fluid become contaminated? *

Water/moisture can be found in nearly all brake systems. Moisture enters the 
brake system in several ways. One of the more common ways is from using old 
or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from 
the surrounding air. Tightly sealing brake fluid bottles and not storing 
them for long periods of time will help keep moisture out. When changing or 
bleeding brake fluid always replace master cylinder caps as soon as possible 
to prevent moisture from entering into the master cylinder. Condensation, 
(small moisture droplets) can form in lines and calipers. As caliper and 
line temperatures heat up and then cool repeatedly, condensation occurs, 
leaving behind an increase in moisture/water. Over time the moisture becomes 
trapped in the internal sections of calipers, lines, master cylinders, etc. 
When this water reaches 212º F the water turns to steam. Many times air in 
the brake system is a result of water that has turned to steam. The build up 
of steam will create air pressure in the system, sometimes to the point that 
enough pressure is created to push caliper pistons into the brake pad. This 
will create brake drag as the rotor and pads make contact and can also 
create more heat in the system. Diffusion is another way in that 
water/moisture may enter the system. 

Diffusion occurs when over time moisture enters through rubber brake hoses. 
The use of hoses made from EPDM materials 
(Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR 
use stainless steel braided brake hose with a non-rubber sleeve (usually 
Teflon) to greatly reduce the diffusion process. 

*What happens if I try to switch from a glycol based fluid to a silicone 
based fluid?*

If silicone is introduced into an older brake system, the silicone will 
latch onto 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. 

*What causes a mushy pedal? *

There are a number of factors some mechanical and some chemical that can 
manifest themselves as a mushy pedal. For this discussion we'll stick to the 
fluid causes.

The most common issue is the amount of dissolved air within the fluid. All 
brake fluid has dissolved air in it (yes, even GS610) the critical question 
is , "How much?" This is explained in greater detail
above<http://www.gs610.com/abc.htm#compressibility>
.

*Silicone (Low Water Tolerant) Brake Fluids*

Silicone based fluids are non-hygroscopic 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. 

*Silicone*

*The development* of Silicone Fluid (DoT 5) began in the late 60's by 
General Electric (Head of R & D on this project was Dr. Torkleson). It was 
orginally developed for the Jim Hall Chaparral Racing Team as a solution to 
the higher temperatures and extreme conditions being realized in Can Am 
racing. Hall had observed, in such races as the Daytonna 24 and the Twelve 
Hours of Sebring, the brake discs (rotors) glowing from the extreme 
temperatures. This led to the involvement of GE and ultimately, the 
development of Silicone brake fluid. 

However, at a Pikes Peak race in the late 60's (I have been unable to pin 
down the exact year) a number of racers using the new silicone brake fluid 
experienced serious brake performance issues. The teams found they would 
leave the starting line with a good solid pedal however, as they continued 
the challenging and tortuous ascent, the pedal would go soft, very much like 
the brake fluid was/had boiling/boiled. This was a consistent phenomena 
amongst the various teams using the silicone brake fluid. No amount of 
additional cooling or any other efforts would change this undesirable 
performance pattern. 

What was ultimately discovered was that Silicone brake fluid had a much 
higher air solubility than conventional glycol based brake fluids. 
Specifically, In the formulation of Silicone and silicone based fluids there 
is 16% ± 3% dissolved air (at normal ambient temperatures re:SAE JV1705, 
Appendix A, paragraph A.2.2.8) relative to the 5% ± 2% dissolved air of 
glycol based brake fluids. As temperatures increase, the dissolved air (78% 
of which is nitrogen) in the fluid begins to return to a gaseous state 
thereby creating a gas or vapor in the fluid. This is really quite similar 
to the effects of boiling brake fluid. Thus resulting in vapor lock and a 
soft pedal. 

This gives Silicone brake fluid and its close cousin, silicone ester (as 
developed later and used by Castrol in SRF Brake Fluid) the very desirable 
property of a very high dry and wet boiling point, However the negative to 
its high air solubility is increased compressibility at ambient temperature 
and greatly exacerbated compressibility at high temperatures and high 
altitudes. 

*Savvy?*

Dale Martin
LEZ
Lewiston, ID 
EAA Technical Counselor

Ronnie
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20050515/ac0a78cf/attachment-0001.html