Brake fluid
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Brake fluid is a type of hydraulic fluid used in hydraulic brake applications in motorcycles, automobiles, light trucks, and some advanced bicycles. It is used to transfer force under pressure from where it is created through hydraulic lines to the braking mechanism near the wheels. It works because liquids are not appreciably compressible. Braking applications produce a lot of heat, so brake fluid must have a high boiling point to remain effective, and must also not freeze under normal temperatures. These requirements eliminate most water-based solutions.
Compatibility issues may exist between DOT 3 / DOT 4 brake systems and DOT 5 fluid. Specifically, DOT 5 silicon fluid may attack and harden some silicon based rubber seals such as caliper piston boots, which will cause the system to leak. Various grades of both DOT3 and DOT 4 fluid exist with different temperature ratings for different applications and manufacturer requirements for fluid types should be followed. [1]
It is important to note the difference between DOT 5 that is silicone-based brake fluid and DOT 5.1 that is polyethylene glycol based similar to DOT 3 and DOT 4.
Some very old British cars use Girling brakes, which are incompatible with DOT3 brake fluid. British-car dealers are careful in observing this precaution; but UK law does not require such observations be taken by commercial garages.
Glycol based fluids are half as compressible as silicone type fluids, even when heated[citation needed]. Less compressibility of brake fluid will increase pedal feel (firmness), but in either case this effect is minimal. The U.S. Army has used silicone brake fluid exclusively since 1982 successfully. Glycols are hygroscopic and will absorb water from the atmosphere, reducing the boiling point of the fluid and degrading hydraulic efficiency. Changing fluid on a regular basis will greatly increase the performance of the brake system, but this is often not a concern in passenger cars. On the other hand, changing fluid at least every several years will preserve the life of brake system components (by removing accumulated water and other contaminants, thereby reducing rust on internal components), and increase the overall reliability of the brake system.
Polyethylene glycol, and other brake fluid ingredients may be corrosive to paint and finished surfaces such as chrome, and thus care should be taken when working with the fluid. Additionally, polyethylene glycol, in the concentrations found in DOT brake fluids, reacts violently, producing a large fireball, with some household chemicals, notably pool care products.[citation needed]
Hotwheelscollectors.com cites that hobby modellers use brake fluid as a safe (if somewhat slow) paint stripper. It is less likely to harm skin and will not harm plastics(although silicone based fluids can distort the detail on plastic models). Brake fluid can also be used as a releasing fluid for screw threads, provided no painted parts are involved.
Components
Mineral-based
- Alkyl ester
- Aliphatic amine
- Diethylene glycol
- Diethylene glycol monoethyl ether
- Diethylene glycol monomethyl ether
- Dimethyl dipropylene glycol
- Polyethylene glycol monobutyl ether
- Polyethylene glycol monomethyl ether
- Polyethylene oxide
- Triethylene glycol monobutyl ether
- Triethylene glycol monoethyl ether
- Triethylene glycol monomethyl ether