[Roadsters] DOT5 (was: Clutch Question)

[Richard Schnoor]

Its been a while since I have worked on my roadsters, but I have some
questions: Forever DOT3 was the standard brake fluid which is hygroscopic
(absorbs water from high humidity air) which then ends up rusting your brake
calipers. Some one told me about DOT 4 which was silicone based & was not
hygroscopic so rusting wasn't a problem for a seldomly driven car. When I
changed over to "4" my brakes were extremely spongy & was accordingly was a
problem with this type of brake fluid. I even built a pressurized auto
bleeder so I could bleed my brakes alone but resulted in no reduction in
sponginess. So what is DOT 5 & 5.1? Do these new fluids address the
sponginess or rusting problem?

On 2/19/08, John F Sandhoff <sandhoff at csus.edu> wrote:
>
> Keep in mind that DOT5 has been reported to be harder to get a
> clean system bleed with. Power bleeding seems to be more
> effective than other methods. Also, DOT5 will find its way thru tiny
> seal imperfections so a system that's leak-free on DOT3/4 may end
> up leaking on DOT5.
>
> I don't know how DOT 5.1 behaves. It's apparently not silicone based
> like 5.
>
> I personally use DOT4 - Castrol GT/LMA for years and years but have
> switched to Valvoline synthetic DOT4.
>
> -- John
>     John F Sandhoff   sandhoff at csus.edu   Sacramento, CA
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-- 
Richard Schnoor P.E.