[Diy_efi] (off topic) Disk pad wear reduction with hydraulic reverse valve ?

[Adam Wade]

--- Mike <erazmus at iinet.net.au> wrote:

> Moving the caliper back by a short amount does not
> *have to* mean the pedal travel is increased at all.

Maybe the laws of physics are different in Australia
than here.

Here, to take up air gap, the piston in the caliper
has to move a like amount.  Which means fluid has to
be moved through the lines in sufficient quantity to
push the piston out that much.

I already gave some sample math.

> Eg. When I service the brakes, the pedal is in its
> top (normal) position. Yet when I remove the pads, I
> can push on the calipers a little - they will
> retract - say 1mm, yet the pedal does not move, the
> oil clearly goes 'somewhere' ;)

Not a sensible example to be using to prove your
conclusion.  With little or no pressure in the system,
the master cylinder piston is fully retracted, and has
a mechanical stop.  A bleed from the master cylinder
allows return of excess fluid into the reservoir.

Using your example, what happens the first time you
step on the brake pedal after pushing the caliper
pistons back in?  What makes you think that would be
any different if the pushing (or pulling) was done by
something other than a screwdriver or c-clamp?

> I'm not sure what you mean be being reminded - I
> dont understand this at all.

No offense, but that is becoming increasingly
apparent.  ;)  You will get the same result as you
would prying the pistons back into the calipers during
a pad change, and then stepping on the brakes the
first time -- a long, sloppy pedal travel without full
pressure at full stroke of the master cylinder piston 
(or not, if you are lucky).

> a.	Normal pedal operation when braking
> and
> b.	Some hydraulic arrangement to retract the pads
> from the discs to *be sure* there is negligible
> chance of drag

Those two objectives are directly opposed.

I still don't see why you want no drag from the pads. 
What is it you are hoping to gain?

> In terms of 'if it aint broke dont fix it' I think
> you should be speaking to religious dogmatic groups
> who are not interested in how technology could be
> improved with a little thought and not to people
> interested in alternate solutions and improving on
> what has gone before.

*sigh*  I've had this discussion here before.  If you
want to get worse results with a great deal more
expense and difficulty, more power to you, but don't
expect anyone else to have spent a lot of time doing
it, and thus being able to tell you how.  You'll
probably have to spend a lot of time and money
experimenting to come to the same conclusion that
aircraft components manufacturers did half a century
ago when they came up with production disc brakes that
have stayed static in design for that time period.

*snip remainder of insulting rant from one who
apparently hasn't had to spend time and money
developing something useful*

The point of development, resumably, is to devote an
appropriate amount of time, money and effort to obtain
a given set of results.  If you wish to aim for
different goals, by all means, but insulting people
who take a practical approach certainly isn't going to
help you reach your goals.

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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