On Thu, 23 Jan 1997, Barry Schwartz wrote:
> Anybody have first hand experience with this happening, whenever I've bled
> the brake's (effectivly creating a leak in one system) the pedal will fall
> to the floor. Unless this dual action only happens when you panic and mash
> the pedal, I can't see that it works. I can understand how it's supposed to
> work but in every car I've bled ( and it's been quite a few ) I never feel
> half a pedal. The one failure I did have, (thankfully right in the
> driveway) was catastrophic, pedal to the floor, NO brakes. That turned out
> to be the master cylinder. So I've yet to be proven that any dual system
> works as stated - I'm sure it must but I just haven't seen it happen? Any
> other thoughts on what I'm missing? - just thought I'd through that out -
Barry, I know exactly what you're saying; I've "been there, done that" as
well. But I've also experienced the systems working as they are designed
to work. In one of those "catastrophic" failures, one will get (in panic,
and perhaps with a pump or two) a stopped pedal (and therefore some
braking action) rather far along on the pedal travel.
IMS, what one experiences is a somewhat "metallic" feel/sound of something
hitting something else rather hard, so long as there is some remaining
functionality in the master cylinder. This is actually accompanied by some
measure of braking action. It might be equal to or less than one might get
from a hard tug of the handbrake lever, depending on which circuit of the
hydraulics has gone south, but it's enough to slow the car in most
circumstances, and it might even be sufficient for some bozos to put up
with for awhile (I don't recommend that, though).
Meanwhile, one shouldn't "feel" anything during a bleeding of the brakes
on a dual-circuit system. If you do feel something, what's that is likely
to be is the PDWA shifting and thereby actuating the warning light
circuit. Yet ANOTHER reason why one shouldn't "test" the brake pedal
during the bleeding process, at least until all four corners have been
bled (or six or eight or however many bleed screws some Volvos have --
yikes!). Again, the factory workshop manuals describe not only the
procedure for bleeding, but the procedure for "recentralising" the PDWA
switch -- open opposite circuit, press pedal until "click" is felt, close
circuit, drive away blissfully content and secure in the knowledge you
have brakes again! ;-)
--Andy
* * * * * * * * * * * * * * * * * * * * * * *
* Andrew Mace, President and *
* 10/Herald/Vitesse (Sports 6) Consultant *
* Vintage Triumph Register *
* amace@unix2.nysed.gov *
* * * * * * * * * * * * * * * * * * * * * * *
|