The fluid was a low viscosity fluid based on diluted alcohol. This system was not engine-driven and did not involve the braking system. Hydragas and Hydrolastic suspension were a widely used form of hydropneumatic suspension, designed by Alex Moulton, and used on British Leyland cars from the 1960s. This system was also used on Rolls-Royce and some Maserati models. Although the two fluids are incompatible, LHM has been universal since 1967, and some older cars have been converted to use it. LHS was hygroscopic and gave problems with internal corrosion. In 1966 Citroën introduced LHM ( Liquide Hydraulique Minéral), a mineral fluid. In 1964 this was improved with the fully synthetic LHS2. Citroën then attempted to improve and standardise the fluid in 1962 with LHS ( Liquide Hydraulique Synthétique), a vegetable/synthetic based fluid. Shell Donax D, Lockheed HD19, Castrol HF were some of them. The first fluids were of variable chemistry, and available from various suppliers. This used a Citroën-specific hydraulic fluid. In the 1950s, Citroën introduced a hydropneumatic suspension system, powered by an engine-driven pump and also used to operate the braking system. Above that threshold makes it DOT 5.Ĭitroën hydropneumatic suspension DOT 5.1 is the non-silicone version of DOT 5, defined by FMVSS 116 as being less than 70% silicone.

Lack of acceptance of silicone-based fluids led to the development of DOT 5.1, a fluid giving the performance advantages of silicone, whilst retaining some familiarity and compatibility with the glycol ether fluids. DOT 5 brake fluid absorbs a small amount of air requiring care when bleeding the system of air. DOT 5 fluid can aerate when the anti-lock brake system is activated. ĭOT 5 brake fluid is not compatible with anti-lock braking systems. Another property is that it does not damage paint. An advantage over other forms of brake fluid is that silicone has a more stable viscosity index over a wider temperature range. Unlike polyethylene glycol based fluids, DOT 5 is hydrophobic. It contains at least 70% by weight of a diorgano polysiloxane. Systems can change fluid only after a complete system changeover, such as a total restoration. It is immiscible with water, and with other brake fluids, and must not be mixed with them. Additionally, these polyglycol-ether-based fluids cannot be mixed with DOT 5.0, which is silicone based.ĭOT 5 is a silicone-based fluid and is separate from the series of DOT 2, 3, 4, 5.1. While a vehicle that uses DOT 3 may also use DOT 4 or 5.1 (a temperature upgrade) if the elastomers in the system accept the borate compounds that raise the boiling point, a vehicle that requires DOT 4 might boil the brake fluid if a DOT 3 (a temperature downgrade) is used. Brake fluid 'in use', or not labeled DOT compliant, is found any color. 116's scope is limited to fluid 'for use'. Īll DOT compliant fluids must be colorless or amber, except for DOT 5 silicone, which must be purple. Their classifications broadly reflect the SAE's specifications, DOT 3 is equivalent to SAE J1703 and ISO class 3, DOT 4 to SAE J1704 and ISO class 4, etc. These are widely used in other countries.

116 defines grades DOT 3, DOT 4, DOT 5 and DOT 5.1, where DOT refers to the U.S. The Federal Motor Vehicle Safety Standards (FMVSS) under FMVSS Standard No. These have counterparts in the international standard, ISO 4925. The Society of Automotive Engineers SAE has published standards J1703, J1704, and J1705, reflecting progressively higher performance for brake fluids.

The International Standards Organisation has published its standard ISO 4925, defining classes 3, 4, and 5, as well as class 5.1, class 6 and class 7 reflecting progressively higher performance for brake fluids. Most Brake fluids are manufactured to meet standards set by international, national, or local organizations or government agencies. Most brake fluids used today are glycol-ether based, but mineral oil ( Citroën/ Rolls-Royce liquide hydraulique minéral ( LHM)) and silicone-based (DOT 5) fluids are also available. It works because liquids are not appreciably compressible. It is used to transfer force into pressure, and to amplify braking force. Hydraulic fluid used for braking applicationsīrake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and some bicycles.

Fmvss no.116 dot 3 brake fluid