Re: Boiling brake fluid Redux

hachiroku <ae86@xxxxxxxxxx> wrote:

>On Sun, 24 Jul 2005 23:03:52 +0000, Gord Beaman wrote:
>
>> "TeGGeR®" <tegger@xxxxxxxxxx> wrote:
>>
>>>Bruce L. Bergman <blPYTHONbergman@xxxxxxxxxxxxxxxxx> wrote in
>>>news:j508e11q4ai470dfhhtfcrg40ks50u0mk3@xxxxxxx:
>>>
>>>> On Sun, 24 Jul 2005 17:25:39 GMT, hachiroku <ae86@xxxxxxxxxx> wrote:
>>>>
>>>>>So, I got the sliders working very nicely. With the car on the jack
>>>>>stands, I started it up and nailed the brakes. The wheel is still
>>>>>sticking, it takes a few rotations for it to free up, but you can still
>>>>>feel it grabbing. Even after a few rotations, it still grabs. Now, my
>>>>>firld is computers; brakes are a 'hobby'. When the piston squeezes the
>>>>>pads, HOW MUCH is it supposed to back off after the release of the
>>>>>pedal? IS it supposed to back off after the release of the pedal?
>>>>
>>>> Sounds normal to me. The calipers aren't supposed to back off at
>>>> all
>>>
>>>
>>>A normally-operating brake caliper piston will retract a bit (1/32" or
>>>so) when you let off the pedal. This provides the pressure release
>>>function.
>>>
>>>As gum builds up on the piston, the retraction action is reduced, then
>>>finally stops, resulting in a dragging brake.
>>
>> We're likely arguing nits here but I don't see why the piston
>> would 'retract' at all...it will be 'shoved back' into it's 'hole'
>> slightly by any slight wobble or unevenness in the turning disc but as
>> long as the caliper is free to move sideways and the piston is free to
>> move in and out then the disc will shove the piston out of it's way (so to
>> speak). I don't see any action in the system that would cause the piston
>> to 'retract' (I equate 'retract' as the piston being 'pulled' back inside
>> it's cylinder and not being 'pushed' into it)
>
>Before I read Teg's response, I'm going to take a guess: there will be
>some retraction (not much) when you take your foot off the brake pedal.
>Think of fluid dynamics: you've pressed the pedal, and introduced pressure
>into the system. Take your foot off the brake, and the release of pressure
>will cause a small amount of back pressure, sucking the caliper back in
>just slightly.
>
>Just an educated guess...

Pretty close Hach...as teg says, the master cyl piston is shoved
back by a spring...now the seal on that piston has to 'unseal' so
as to be 'ready' to 'grab' more fluid if it's necessary so there
has to be a very slight negative pressure on the fluid in the
system as it unseal and this is what moves the slave pistons
slightly. Remember that there's four slave cylinders and they're
all much bigger than the master cyl therefore they'll all move
only a slight amount...that sound about right Teg?
--


-Gord.

"I'm trying to get as old as I can,
and it must be working 'cause I'm
the oldest now that I've ever been"
.

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