'68 Mustang bad brakes...

All new hardware, including master cylinder and the fronts were
upgraded to disc. The only thing that hasn't been replaced is that
directional valve 'thingy' which, I'm guessing, acts as a failsafe.
Have bled the brakes numerous times, however, the pedal keeps
travelling to the floor. Is that directional valve the problem? The
only other symptom I can relate is that when the pedal is pressed
(when bleeding), fluid shoots back into the master cylinder reservoir.
Shouldn't it only shoot back when the brakes are released?

Help!
Darryl.
(actually, it's for a buddy, but who's keeping track).

Just from your description, it sounds like you have a bad master cylinder, it happens even
to new ones sometimes. If you pump the brakes with the lid off the master you will get
fluid spraying around so that part is somewhat inconclusive (but don't leave the lid off!)
StuK





"Darryl" > wrote in message
...
> All new hardware, including master cylinder and the fronts were
> upgraded to disc. The only thing that hasn't been replaced is that
> directional valve 'thingy' which, I'm guessing, acts as a failsafe.
> Have bled the brakes numerous times, however, the pedal keeps
> travelling to the floor. Is that directional valve the problem? The
> only other symptom I can relate is that when the pedal is pressed
> (when bleeding), fluid shoots back into the master cylinder reservoir.
> Shouldn't it only shoot back when the brakes are released?
>
> Help!
> Darryl.
> (actually, it's for a buddy, but who's keeping track).

(The only thing that hasn't been replaced is that directional valve
'thingy')

Do you mean the proportioniong valve? You'll need one for a disk/drum setup.
Did you bleed the master cylinder?


"Stuart&Janet" > wrote in message
...
> Just from your description, it sounds like you have a bad master cylinder,
> it happens even
> to new ones sometimes. If you pump the brakes with the lid off the master
> you will get
> fluid spraying around so that part is somewhat inconclusive (but don't
> leave the lid off!)
> StuK
>
>
>
>
>
> "Darryl" > wrote in message
> ...
>> All new hardware, including master cylinder and the fronts were
>> upgraded to disc. The only thing that hasn't been replaced is that
>> directional valve 'thingy' which, I'm guessing, acts as a failsafe.
>> Have bled the brakes numerous times, however, the pedal keeps
>> travelling to the floor. Is that directional valve the problem? The
>> only other symptom I can relate is that when the pedal is pressed
>> (when bleeding), fluid shoots back into the master cylinder reservoir.
>> Shouldn't it only shoot back when the brakes are released?
>>
>> Help!
>> Darryl.
>> (actually, it's for a buddy, but who's keeping track).
>
>

Thanks for the quick replies Stu and Mark.

We're onto the second master cylinder. Both were bled properly
although we can't get pressure to build up in the lines. If the lines
are pressurized slowly as the brakes are pumped, the pedal will always
travel to the floor. If pumped quickly, they will pressurize but
we're not getting any air out!

>(The only thing that hasn't been replaced is that directional valve
>'thingy')
>
>Do you mean the proportioniong valve? You'll need one for a disk/drum setup.

Yes, the proportional valve. I think it's stock for the all drum
setup. There's another one for front disc/rear drum?

>Did you bleed the master cylinder?

Yah.

Thanks again,
Darryl.


>> Just from your description, it sounds like you have a bad master cylinder,
>> it happens even
>> to new ones sometimes. If you pump the brakes with the lid off the master
>> you will get
>> fluid spraying around so that part is somewhat inconclusive (but don't
>> leave the lid off!)
>> StuK
>>
>>
>>
>>
>>
>> "Darryl" > wrote in message
>> ...
>>> All new hardware, including master cylinder and the fronts were
>>> upgraded to disc. The only thing that hasn't been replaced is that
>>> directional valve 'thingy' which, I'm guessing, acts as a failsafe.
>>> Have bled the brakes numerous times, however, the pedal keeps
>>> travelling to the floor. Is that directional valve the problem? The
>>> only other symptom I can relate is that when the pedal is pressed
>>> (when bleeding), fluid shoots back into the master cylinder reservoir.
>>> Shouldn't it only shoot back when the brakes are released?
>>>
>>> Help!
>>> Darryl.
>>> (actually, it's for a buddy, but who's keeping track).
>>
>>
>

>>(The only thing that hasn't been replaced is that directional valve
>>'thingy')
>>
>>Do you mean the proportioniong valve? You'll need one for a disk/drum setup.
>
>Yes, the proportional valve. I think it's stock for the all drum

Make that the *proportioning valve.

>>(The only thing that hasn't been replaced is that directional valve
>>'thingy')
>>
>>Do you mean the proportioniong valve? You'll need one for a disk/drum setup.
>
>Yes, the proportional valve. I think it's stock for the all drum
>setup. There's another one for front disc/rear drum?

Ok, we might not be talking about the same proportional valve. He's
calling it a pressure balance sensor block which to me sounds like a
proportioning valve but he says it's different. Apparently this one
is new (aftermarket) and it has a thumb screw to adjust the pressure
to the brakes (i.e., reduce it to the rears and increase to the
fronts). Right now, he barely has rear brakes and nothing on the
fronts so we're going to remove that block and see what happens.

Any other suggestions?

Darryl.

Darryl wrote:
>
> All new hardware, including master cylinder and the fronts were
> upgraded to disc. The only thing that hasn't been replaced is that
> directional valve 'thingy' which, I'm guessing, acts as a failsafe.
> Have bled the brakes numerous times, however, the pedal keeps
> travelling to the floor. Is that directional valve the problem? The
> only other symptom I can relate is that when the pedal is pressed
> (when bleeding), fluid shoots back into the master cylinder reservoir.
> Shouldn't it only shoot back when the brakes are released?
>
> Help!
> Darryl.
> (actually, it's for a buddy, but who's keeping track).
be the master cylinder is bad(its the oring on the part that goes into
the opening --the main piston... had it on a 66 mustang.. had the brakes
worked on at a shop back in the late 60's... the pedal would stay up but
if you leave a little pressure off the pedal it would travel to the
floor.. the mechanic(old man) told me that someone must have shoved the
pedal down to far when they bled the brakes... that would mess up the
master cylinder piston(O-ring)..... it hits an area that it never does
when the brakes have fluid in them so it then gets distroyed by this NEW
area that it hits during bleeding....kinda makes sense if that is your
problem.... hope this helps.

All post and replies kind of vague on a few points. the distribution block
is the brass unit directly down stream of the master cylinder on your car it
should have a wire coming out of it. This is what will light up the brake
waring lamp in your guage cluster.
You spoke of bleeding the master cylinder, have you bleed both rear wheel
cylinders, and both front calipers? On a swap as you mentioned this may
require filling the master cylinder several times.
The proportioning valve mentioned in other posts is to limit the flow of
fluid to the rear wheels as the calipers take much more fluid to operate.
Fluid spraying back into the master cylinder while holding (not pumping) the
brake pedal down is a sure sign of compressed air in your system.

hope this helps
walt
"Darryl" > wrote in message
...
> All new hardware, including master cylinder and the fronts were
> upgraded to disc. The only thing that hasn't been replaced is that
> directional valve 'thingy' which, I'm guessing, acts as a failsafe.
> Have bled the brakes numerous times, however, the pedal keeps
> travelling to the floor. Is that directional valve the problem? The
> only other symptom I can relate is that when the pedal is pressed
> (when bleeding), fluid shoots back into the master cylinder reservoir.
> Shouldn't it only shoot back when the brakes are released?
>
> Help!
> Darryl.
> (actually, it's for a buddy, but who's keeping track).

Darryl...
Been there, done that. I can almost promise you the master cylinder does
not have a big enough bore to push enough fluid for the new disks... I've
been there. What is the bore size of the master cylinder? I'll bet it's
less than a 1" bore...like a 7/8"?? I had to go to a 1 1/8" bore to push
enough fluid to make the fronts work.
Let me know what bore size you are using for the master cylinder?
Mark

>Darryl...
> Been there, done that. I can almost promise you the master cylinder does
>not have a big enough bore to push enough fluid for the new disks... I've
>been there. What is the bore size of the master cylinder? I'll bet it's
>less than a 1" bore...like a 7/8"?? I had to go to a 1 1/8" bore to push
>enough fluid to make the fronts work.
> Let me know what bore size you are using for the master cylinder?
>Mark

Hi Mark,

I would let you know the bore size if I knew which measurement that
is! The push-rod bore is 1/2"--this is bored into what looks like an
aluminum part that is retained by a snap ring--the apparent outer
diameter of this part is 1"

I suppose that I can pop off that snap ring and take a closer look.
Can I pick up an oversized master cylinder or is it possible to have
this one machined?

Thanks for the feedback,
Darryl.