Brake Fluid

 
 
Brake fluid is a type of hydraulic fluid that is used in the hydraulic brake and hydraulic clutch, in the uses of cars, motorcycles, light trucks, and some grades. It is used to convert force into pressure, and to increase brake force. It is suitable for this task as the liquid is by nature incompressible.
Most brake fluids used are glycol-ether based, or mineral-based Citroen and Rolls-Royce liquide hydraulique minéral (LHM), as well as silicone-based fluids.
Brake fluids must meet certain requirements as defined by various standards set by organizations such as the Society of Automotive Engineers (SAE), or equivalent local organizations. For example: brake fluids sold in North America are categorized by the US Department of Transportation (DOT) under their own classifications such as ‘DOT 3’, ‘DOT 4′, and DOT 5 5’ silicon-based. All liquids approved in the United States for road use must be colorless (transparent) or amber, except for Dot5 which is a different base (silicone), which must be purple.  
 
Characteristics of brake fluid:
Brake fluid must have certain characteristics and meet certain quality standards for the braking system to function properly.
Boiling point:
Brake fluid is subject to very high temperatures, particularly in the wheel cylinders of the drum brakes and in the saddle calipers of the disc brake. Therefore, brake fluid must have a high boiling point to avoid evaporation. Evaporation is a big problem here because the vapor is more compressible than the liquid, and thus impedes the hydraulic transmission of brake force to the tubes (the brakes will fail to stop the car).
Quality standards refer to the “dry” or “wet” boiling points (boiling temperature) of brake fluid. The wet boiling point, usually much lower than the dry boiling point (but higher than most operating temperatures), refers to the boiling point of a liquid after a certain amount of moisture has been absorbed. Dot 3 and Dot 4 glycol ether based brake fluids have a hydrophobic property, which means that they absorb moisture from the atmosphere at normal humidity levels. Dot 5 silicon based fluids can maintain an acceptable boiling point during the entire operating life of the fluid.
Viscosity:
To ensure reliability /consistent operation, brake fluid must maintain a constant viscosity over a wide range of temperatures, including extreme cold. This is especially important on systems with ABS, traction control,
Corrosion resistance:
brake fluid should not cause corrosion to the internal metals used in the various brake parts. It must also protect these parts from moisture entering the system. Additives (wear inhibitors) are added to the original brake pads to achieve this. Silicon-based fluid has less corrosion effect on car paint, unlike glycol ether-based fluids.
Compressibility:
The brake fluid must be maintained at a low level of compressibility, even at varying temperatures, to accommodate different environmental conditions. This is important to ensure a consistent feel to the brake pedal/pedal. As the compressibility increases, the pedal travel distance increases for the same brake force acting on the wheel.
DOT 5 silicon-based brake fluid has a higher compressibility (more compressible) than other DOT 3 and DOT 4 brake fluids, resulting in a spongy feeling in the brakes when the pedal is pressed.
 

Characteristics of common braking fluids
	Dry boiling point	Wet boiling point	Viscosity limit	Primary constituent
DOT 2	190 °C (374 °F)	140 °C (284 °F)	?	Castor oil/alcohol
DOT 3	205 °C (401 °F)	140 °C (284 °F)	1500 mm2/s	Glycol Ether
DOT 4	230 °C (446 °F)	155 °C (311 °F)	1800 mm2/s	Glycol Ether/Borate Ester
LHM+	249 °C (480 °F)	249 °C (480 °F)	1200 mm2/s	Mineral Oil
DOT 5	260 °C (500 °F)	180 °C (356 °F)	900 mm2/s	Silicone
DOT 5.1	260 °C (500 °F)	180 °C (356 °F)	900 mm2/s	Glycol Ether/Borate Ester

Wet boiling point defined as 3.7% water by volume.
Wet boiling point is defined as (the boiling point of a liquid in the presence of water of 3.7% by volume).
Brake Fluid
https://en.wikipedia.org/wiki/Brake_fluid  Brake fluid
http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid  Brake fluid**
https://jimsgarage. wordpress.com/2007/01/09/dot-3-dot-4-and-dot-5/  DOT 3, DOT 4 and DOT 5
 
Service and maintenance:
Most auto experts agree that glycol-based brake fluid such as Dot 3, Dot 4, Dot 5.1 should be flushed, or changed, every 1-2 years (non-racing conditions). Some auto manufacturers recommend changing the fluid periodically to ensure reliability and safety. Once the fluid is placed in the system, moisture enters the fluid via rubber hoses/tubes and rubber gaskets, and eventually the fluid must be changed when the water content becomes too high. This can be checked by an electronic test meter or by a commercially available test strip to measure the moisture content of the liquid. The moisture test strips have been withdrawn from the market as they absorb moisture from the air before they are used. The corrosive additives present in the fluid deteriorate over time. Degraded state additives cause corrosion of the brake system. The first metal to be corroded by the system is copper. You can determine when it is time to replace the brake fluid when the copper ions in the fluid have reached 200 ppm (200 parts per million). The new fluid should in all cases be kept in a closed container/pack to avoid moisture penetration. Therefore, brake fluid is sold in small packages, so as not to keep the remaining fluid for future use.
Dot 5 brake fluid is silicone-based, so all of the above in service and maintenance do not apply to it. Ideally, silicone fluid should only be used in non-ABS systems that did not previously have a glycol-based fluid. Any system that uses a glycol-based liquid will contain moisture; The fluid is distributed/dispersed throughout the system and the brake fluid (based on glycol) contains corrosion inhibitors. Silicone fluid does not allow moisture to enter the system, but it does not get rid of any of it in the system (therefore, it is not recommended to replace or mix different types of brake fluids in the same car). Any system with dry silicon fluid does not need to be replaced at intervals, only when one part of the system is replaced. Silicon is widely used in very cold weather.
 
When the level of brake fluid in the master cylinder reservoir drops, a fluid (with the same specifications) is added to correct the level, but if this is repeated, it must be checked, detected and repaired. The brake fluid level naturally decreases as the friction linings wear out as brake fluid replaces the worn space. The level of brake fluid also decreases due to leakage, which leads to a loss of hydraulic pressure and consequently a loss of brake capacity. Modern cars have a dual brake circuit to ensure that there is no complete hydraulic failure.
* Brake fluids are of different dot rating and should not be mixed together (different base, glycol and silicone). The same dot rating should be used each time fluid is added or replaced. Dot 5.1 can replace Dot 4 and Dot 3. Dot 4 can replace Dot 3. Dot 5 should not be mixed with any glycol based liquids, mixing them together will lead to corrosion/rust due to moisture retention.
 
Service brake fluid:

•         Add/supply brake fluid.
•         Detect the leak, and fix the problem.
•         Check the condition of the brake fluid.
•         Drain the air from the circuit.
•         Oil change and replacement.
•         Flush the oil system.
•         Disposal of old and used oil residues.

 
 
Brake fluid safety tips:
 Brake fluid is toxic, flammable and can damage vehicle paint.

•        Keep the liquid away from children.
•        Avoid exposure of the skin and eyes to the liquid.
•        If the eye is exposed to liquid, rinse the eye with plenty of water, and get medical attention immediately.
•        If the liquid has been swallowed, refer to a medical professional immediately, and indicate the type of liquid that was swallowed.

 
Brake fluid handling tips:

•        Always keep brake fluid in the original can, and make sure the cap is closed tightly. And keep it in a clean, dry place without moisture.
•        Never use or reuse brake fluid that has been drained from the brake system and any brake fluid that was in an open can, as brake fluid quickly becomes contaminated with dirt, air and moisture.
•        If using Dot 5 brake fluid, do not add any Dot 3 or Dot 4 brake fluid to it. They will interact poorly together and will cause the brake system to rust.
•        Do not use brake fluid with a lower dot rating than recommended in the maintenance manual (dot 3 instead of dot 4). Brake fluid with a lower dot rating may boil over and cause squishy performance.
•        Do not pour Dot 3, Dot 4, Dot 5.1 glycol based liquid on the car paint, as this will damage the paint. But dot 5 has no harmful effect on paint.
•        Do not completely fill the master cylinder reservoir with brake fluid (do not exceed the max level/mark). Always leave a place where the liquid can expand when it is hot. Conversely, never allow the brake fluid level to become empty or below the min mark.
•        Never clean brake system parts with a mineral-based solvent such as kerosene, gasoline, acetone, or paint thinner. These fluids will damage the rubber parts and wires and cause them to soften, distort, or swell, causing the system to malfunction.
•        Depending on the additives used for brake fluid, the fluid may or may not be hazardous. It will likely become dangerous if it becomes contaminated with brake cleaner from a spray can, which contains Chlorinated solvents.
•        Collect brake fluid in a separate container, marked marked and closed closed and notified to recycle or dispose of it in an environmentally friendly manner.
•        Do not put brake fluid in a container of used oil.
•        Do not drain brake fluid into a drain or onto the floor.
•        Do not spray the spray brake cleaner near brake fluid.