<VV> brake fluid

[James Davis]

Not to argue the point but the reason there is a DOT 5 and a DOT 5.1 
specification is the dry (500 F)and wet (356 F) boiling points are 
the same for both fluids.  DOT 5.1 is a borate ester and is used a an 
anti wear additive in most synthetic motor oil.  It is moderately 
hygroscopic.  Unlike DOT 5 (a silicone based fluid), rapid pulsing of 
the brake petal will not induce air bubbles into DOT 5.1 (the reason 
DOT 5 is not used in anti-lock brake systems). Both fluids are old 
technology and there are many better brake fluids out there.  Some 
have wet boiling points above 600 degrees.   Some are reasonable 
priced and some are very expensive.
Jim Davis


At 03:37 PM 6/22/2007, Michael Kovacs wrote:
>DOT 5.1, like DOT 3 and DOT 4, is a polyethylene glycol-based fluid 
>(contrasted with DOT 5 which is silicone-based). Fluids such as DOT 
>5.1 are hygroscopic and will absorb water from the atmosphere. This 
>degrades the fluid's performance by drastically reducing its boiling 
>point. In a passenger car this is not much of an issue, but can be 
>of serious concerns in racecars or motorcycles.
>
>MIKE KOVACS
>  _________________