Additional Information

To obtain the best performance from racing brake systems, bleed the system thoroughly, immediately prior to each event using AP Racing brake fluid from a new sealed bottle. This is particularly important in wet or humid conditions or when the brakes are excessively hot. Always use fresh fluid and replace bottle cap when not in use. Never re-use brake fluid.


The use of a high temperature fluid should not be used as a substitute for proper brake cooling. Brake temperatures can be determined using AP Racing temperature stickers (CP2650-11) and thermal paints (kit No CP2649-5). If you require advice please
Contact Us.


SILICONE BRAKE FLUIDS – A WORD OF CAUTION

AP RACING NEITHER MARKETS SUCH FLUIDS NOR RECOMMENDS THEIR USE WITH OUR OWN OR ANY OTHER BRAKING SYSTEM

Virtually all of the problems with Silicone Brake Fluids relate to:-
Long/spongy pedal
Sudden loss of brakes
Hanging on of brakes

They reflect certain properties of silicone fluids identified by us over many years and recently ratified in SAE publications, namely:-
High ambient viscosity
High air absorption
High compressibility
Low lubricity
Immiscibility with water

Research has shown that the relationships between problems reported and properties identified may be expressed as follows:-

- Long /Spongy Pedal

a) Compressibility, up to three times that of glycol based fluids
b) High viscosity, twice that of glycol based fluids, leading to slow rates of fill and retention of free air entrapped during filling, and hence bleeding difficulties.

- Sudden loss of brakes

a) Air absorption. Gasification of absorbed air at relatively low temperature produces vapour lock effect.
b) Immiscibility (failure to mix) with water. Whilst the presence of dissolved water will reduce the boiling point of glycol based fluids any free water entrapped in silicone-filled systems will boil and produce vapour lock at much lower temperatures (100°C or thereabouts)

- Hanging on of brakes

a) Low lubricity. In disc brake systems the sole mechanism for normalisation of system pressure upon release of pedal pressure is a designed-in tendency of seals to recover to their ‘at rest’ attitude. Low lubricity works against this tendency.
b) High viscosity exacerbates the effect of (a) above.
It should not be assumed, therefore, that the high price of silicone fluids implies higher performance in hard driving or even normal road use.

AP Racing glycol based fluids do not contain the adverse properties described above. The recently introduced
Factory R DOT 5.1 which exceeds the performance criteria of DOT 5 (Silicone), is suitable for all conditions likely to be encountered in modern driving conditions.