Spongy brakes *sometimes*

[TEX TERRY, II]

From: Helge Wunderlich <helgeww at start.no>
(snip)
I have checked for cracks and moisture.
> If the hoses are
>faulty (worn from use or age), then the hoses will swell during pressure
>application, which may cause the sponge feeling.
Do you think it could be periodic ? I'd think it would be more
constant if that was the case.
(snip)

What I have learned, through the years, is that, as the brake fluid
temperature rises, there is a tendency, due to the swelling of aged hoses
(worn on the inside), for some of the "pressure" to be  directed to the
inside of the hose, instead of all of the pressure being directed to the
caliper (or cylinder).  The "spongy" feeling is the swelling of the hose.
This may not occur until the engine heat has caused the brake fluid to
increase in temperature.  There may be no outward signs of leaking brake
fluid on the hoses.  If you use a "paper tape" (tape that will tear easy if
stretched) to tightly wrap the outside of the hose (after cleaning the hose
of dirt residue), then if the hose is in real bad condition, the hose would
swell and tear the tape.  If the hose is just starting to get worn on the
inside, then the tape may not be torn, but the inside of the hose is still
going to be flexing with the fluid pressure, giving you the spongy feeling,
and eventually the breakdown of the inside of the hose material will cause
the hose to leak.

Tex Terry, II
83 5kt sedan (non-quattro)
Franklin, PA  USA