Re: [MV] Re: Silicone Brake Fluid - PS

Alan Bowes (
Tue, 19 Oct 1999 13:28:54 -0600

Buzz wrote:

> Sponginess? I've got mil spec silicone brake fluid in my MUTT and the pedal is up
> to the top and hard as a rock.
> Buzz

Hi Buzz. I didn't say that the brakes would necessarily feel spongy. In fact, I
haven't had spongy-feeling brakes with silicone fluid either. Generally, if the brakes
are properly bled, there won't be any problem.

However, being that silicone fluid is relatively more compressible than glycol fluid,
a rise in temperature or a small-to-large diameter ratio (master cylinder-to-wheel
cylinder) will tend to "soften" the feel of the pedal more than it will with glycol
fluid. And, as I mentioned, a lot of people have probably also had air bubbles trapped
in the line, which could add a lot more sponginess to the feel of the brakes.


> On Tue, 19 Oct 1999 11:26:56 -0600, you wrote:
> >I just wanted to add that all brake fluids are compressible to some degree, but
> >silicone fluid is several times more compressible than glycol fluids, especially
> as
> >temperature goes up. Some people have complained about a slightly spongy feel
> when
> >using silicone fluid, but that will depend a lot on the individual vehicle; more
> >specifically it will depend on the relative ratio of the master cylinder diameter
> >to the wheel cylinder diameter(s). The smaller the master cylinder diameter
> >relative to the wheel cylinder diameter(s), the more likely it is that you'll
> feel
> >some sponginess, especially if the brakes and fluid are hot. Naturally, if there
> >are any trapped bubbles, they will increase any sponginess.
> >
> >Alan

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