REFLECTOR: DOT 5 Compatability

[Wayne]

O0ps!
Does anyone know of a good way of removing DOT 5.1 from my brakes? It is all I have ever used in my brakes. I was not aware of the fine point of 5 vs. 5.1.
Wayne
  ----- Original Message ----- 
  From: Ron Brown 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Sunday, May 15, 2005 8:19 AM
  Subject: Re: REFLECTOR: DOT 5 Compatability


  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



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