ok, so we replaced the master cylinder, we bench-bled it as directed, then bled
the brakes. started it up, and instead of a full-floor mush pedal as before it
was now like the engine was off, a hard pedal with little grab requiring a very
hard push to stop the truck, and the engine revved slightly when pushing the
brakes. obvious vacuum problem there and the hard pedal is indicative of power
booster failure. soooooo, we replace that as well, and we still have a mushy
pedal. although mushy, it does grab hard at some point and we can get the
brakes to lock up, but it aint at all right.

any other ideas on why we have still have mush? when bleeding, starting with
the right rear, how many pumps or how much volume should you bleed to feel sure
that the entire length is flushed? we are using the little magnetic bottle
bleed kit from auto zone.

david

"Surfgeotwo" <surfgeotwo (AT) aol (DOT) com> wrote

Dave,

Bleed them out the ol' fashioned way (without your bleed kit or vacuum
pump). Two slow pumps, hold pedal, open bleeder, when pedal hits the floor
close the bleeder and pump em' up again. I like to put a clear hose on the
bleeder valve so I can "see" what's coming out, including little tiny
bubbles that you might miss using another method. When there are no
bubbles, it's bled. It really varies as to how many pumps/how much volume
is required. Seeing as how you opened the lines at the very beginning of
the brake circuit, it's gunna take awhile, as the air at the beginning of
the line needs to make its way all the way to the other end.

If it's bled correctly and you still have a low/mushy pedal, check the
tightness of the rear brakes, as out-of adjustement rears will cause a low,
mushy pedal. Year, make and model?

Doc

snipped.....

thanks doc - its a '96 chevy z-71 w/350

oh yeah, and its red .. ;-)

"Surfgeotwo" <surfgeotwo (AT) aol (DOT) com> wrote

Oh, the red ones require a special tool to bleed the
brakes.......................that must be why you're having such
difficulty...............he he he he.

Doc

Don't believe him, he did the same work to his C1500 and it's still all
mushy..

GMC Gremlin

"Surfgeotwo" <surfgeotwo (AT) aol (DOT) com> wrote

"GMC Gremlin" <death (AT) becomes (DOT) me> wrote

I think I've been around on this ng long enough for people to know my advise
is trustworthy. You on the other hand have not, and are currently batting
around .200 per way of "advise."

If you were someone else on this ng, who would you listen to? :-)

Doc

arrrrrrrrrrrrrrgh

ok, pumped the brake 4 times slowly, then held - it was at about 3/4 down -
port (right rear) opened and i felt it go to the floorboard and then closed the
port. repeat. same thing - and bubbles were noted. however, from then on -
about 7 repetitions, the pedal went all the way to the floor before opening the
port each time - but fluid still came out when opening the port, just not much.
no more bubbles from the 4th time to the 7th so we moved to the left rear -
-same thing - the pedal went all the way to the floor before opening the port,
but fluid still came out and there were bubbles the first 2 or 3 tries, but not
the last 4 or 5. did all 4 the same way, still all the way to the floor.

certainly this would be the exact symptoms one would expect if there were a
leak somewhere, but after all that i would expect the leak would be very
evident. can it leak within the abs and not be noticeable????

tomorrow morn we will check the rear brakes, but i cant imagine them being so
loose that they would absorb all the hydraulic effort. should we maybe try the
vacuum method of bleeding and run about 5 gallons of fluid through each line to
make dawggone certain it is entirely flushed???

this is aggravating, on a 1 to 10 scale i would say i can do up to 7 or so
skill-level work, so i dont think we are complete idiots - . but then again i
am a surfer from texas so who knows?? ;-)

Inline...................................

"Surfgeotwo" <surfgeotwo (AT) aol (DOT) com> wrote

Hmmmm, not good.

No, not really. The ABS system is in bypass mode when it's not running, so
it's unlikely that any air would have made it's way into the ABS hydraulics.
As for the ABS leaking, I've never heard of that before.

If you're not getting any hydraulic pressure, this effort might be in vain.

He he. Try this. Open the Master cylinder reservoir and watch the bottom
of the reservior as someonle else VERY SLOWLY depresses the pedal. If they
press it too fast you'll get wet! You should see two mini-geysers of fluid
coming up, one from each reservoir. Are there any bubbles in this stream of
fluid? After pumping them up a few times is the master cylinder fluid
foamy?

Doc

saw the "geysers, and no, no foaminess or bubbles.

wait a minute, maybe i AM an idiot after all. is this supposed to be done with
the engine running or not?

damn, that was a hard question to ask. good thing embarrassment doesnt
translate well into ascii... ;-)

"Surfgeotwo" <surfgeotwo (AT) aol (DOT) com> wrote

You'll want to bleed them with the engine off. How have you been doing it?

Doc