<VV> Compressibility of DOT-5 (Silione based brake fluid)

Jim Simpson simpson661 at gmail.com
Sun Jan 27 15:42:36 EST 2019

There is some basis for the idea that DOT-5 based brake fluid is somewhat
compressible.  From what I've been able to determine, the issue is
entrained air, not the fluid itself.  If air is somehow mixed in (from
shaking the can or not pouring it very carefully), it takes a very long
time for the tiny air bubbles to come out.  Much, much slower than from
DOT-3 fluids.

It's the bubbles that compress!  There might some slightly greater fluid
compressiblity of the DOT-5 than DOT-3, but the entrained air is frequently
the issue.

The moral of the story is to be very careful when filling a system with
DOT-5 brake fluid to ensure the fluid isn't shaken or capturing air as it
is poured.

Jim Simpson
Group Corvair

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