Brake Fluids (A hopefully definitive thread)

[cheezemonkhai]

Following much discussion about brake fluids i figured a mini thread to pull together the information and keep it somwhere useful it can be found was called for.

So to summarise you have the following brake fluids that you can readily buy:

• DOT 3
• DOT 4
• DOT 5
• DOT 5.1 (Also knows as Super DOT 4 or DOT 4 Plus)
• LHM

DOT 3, DOT 4 and DOT 5.1 are all compatible and as such can be 'mixed'

DOT 5 is silicon based and MUST NOT be mixed with any of the other fluids.

LHM this is mineral based and is only for use in citroens with the hydraulic suspension (or rolls royce cars with the same set up). This MUST NOT be used in place of a DOT rated brake fluid.

Super DOT 4

To summarise super DOT 4 is another name for a fluid which meets or exceeds the DOT 5.1 standard.

DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements and because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern.

The referal of these fluids as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids is done because they are more similar to a conventional DOT 4 fluid by chemistry than they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially comprised of Borate Esters

This information was taken from product data sheets and the article at:
StopTech : Balanced Brake Upgrades

Which Brake Fluid

Generally DOT 4 will suffice for your car, however should you intend to be driving in a brisk fashion then DOT 5.1 may be a better choice due to the higher dry and wet boiling points.

The wet boiling point is what is important, as after the fluid has been in the brake system for a year this is most likely how the fluid will behave in real use.

Some car suppliers (including halfords) recommend DOT 5.1 fluids for any cars which use standard DOT3/4 fluids and have ABS.

[john_grant358]

Good thread, nice one!