On Sun, 19 Feb 2017 07:31:44 -0700, Brewster wrote:


On 2/16/2017 1:57 PM, wrote:
On Thu, 16 Feb 2017 11:17:16 -0500, Jack wrote:

On 2/14/2017 9:07 PM, wrote:

I was told that the brake fluid should be replaced on shedule to keep
the brake lines from rotting out.

First I ever heard of that.
Brake fluid is hygroscopic - it attracts moisture -and the moisture
can cause corrosion inside the lines and cyls. The water tends to end
up in the low spots. On newer vehicles where the master reservoirs are
sealed much better thasn in the past (with rubber bellows etc) it is a
LITTLE less critical (3 years rather than 2 often recommended). The
new synthetic brake fluids stand up a wee bit better too.



This was a few years ago, but I remember the old standby DOT 3 fluid
(maybe DOT 4?) was considered permanent and was not prone to being
hydroscopic. The newer fluids, synthetic (DOT 5 ?) was very prone to
absorbing moisture and had to be changed regularly. Given the much
higher cost and no real advantage for non-performance driving. the idea
of "upgrading" soon left my thoughts.
I had a number of vehicles from the 60's and 70's, all with non
stainless lines. Never any problems (though these were all southwest
vehicles).

-BR

Dot3 and DOT5 were VERY hygroscopic. Law required fluid only be sold
from a sealed can.( I was a mechanic back in the late sixties)
DOT5 is hydrophobic, meaning moisture is not absorbed.
All fluids up to DOT4 were poly-glycol based while DOT5 is a silicon
based synthetic. NEVER mix Dot5 with Dot4 or below. Dot5.1 is an
acceptable substitute, but NEVER mix it with Dot5. Any vehicle using
DOT5 should be CLEARLY LABELLED as such. It is technically illegal to
use DOT5 in a vehicle not originally built with and spec'd for DOT5
fluid.

NO DOT fluid has EVER been sold as or considered to be a "permanent"
fluid.. Look up "wet boiling point" and "dry boiling point for DOT
Brake Fluid.. PolyGlycol fluids absorb up to 3% water per year....