Front brakes dragging, no rear pressure, all disc
 

Hi all,

The short version is that my front brakes are dragging quite
heavily. The long version is that I have a car with 4 wheel disc
brakes and no ABS. Each caliper only has a single piston. My car has
been parked through winter, so a few months and now the front brakes
are dragging very heavily, to the tune of going 500 feet you cannot
touch them. Needless to say the front brakes lock up instantly if you
touch the brakes. The rears however appear to do nothing. I jacked up
the rear and tried bleeding the brakes but there's absolutely no
pressure or fluid coming out of the rear. My lines seem solid and I'm
not low/losing fluid. Checking the front brakes this past weekend I
found that the pads themselves were rusted to the track they're
supposed to ride in, so I sanded them clean and lubricated them and
they slide nice now, so should be able to release if that was the
problem. But they still drag. Not quite as heavily now and the fronts
don't lock up as easily.

I've thought of stuck/failing calipers, but it's weird both in the
front would fail at once, the brake fluid is clear with no debris, even
coming out of each of the calipers on the front. So I would thinking
combination/proportioning valve problem with the lack of rear pressure,
but even at that there shouldn't be a constant slight pressure on the
fronts. The vacuum boost assist seems to work well, but the overall
pedal pressure is lower than I'd expect. My proportioning valve has a
bleeder on it and bleeding this a half dozen to a dozen times you can
get pressure to the rear for one pedal press. Perhaps there's air in
the rear lines or break I'm missing? But I don't lose fluid and see no
leaks, and it seems strange I have to bleed a dozen times to move the
valve enough to get even a little pressure to the rears.

The basic system is two lines off the master cylinder into the
proporitioning valve, and then they each have splitters to feed
left/right of rear or front.

Any help would be appreciated, I'm not really sure what to try short of
replacing the master cylinder and maybe the booster to be sure, but
that's an expensive proposition, even a test to prove the master was
bad would be useful.

Thanks,
Chris

First thing to do here is check the brake fluid is not contaminated with
say, p/s fluid for example. If the fluid in the master is oily or the seal
on the cover is wrinkled up, this is your problem.
> wrote in message
ps.com...
> Hi all,
>
> The short version is that my front brakes are dragging quite
> heavily. The long version is that I have a car with 4 wheel disc
> brakes and no ABS. Each caliper only has a single piston. My car has
> been parked through winter, so a few months and now the front brakes
> are dragging very heavily, to the tune of going 500 feet you cannot
> touch them. Needless to say the front brakes lock up instantly if you
> touch the brakes. The rears however appear to do nothing. I jacked up
> the rear and tried bleeding the brakes but there's absolutely no
> pressure or fluid coming out of the rear. My lines seem solid and I'm
> not low/losing fluid. Checking the front brakes this past weekend I
> found that the pads themselves were rusted to the track they're
> supposed to ride in, so I sanded them clean and lubricated them and
> they slide nice now, so should be able to release if that was the
> problem. But they still drag. Not quite as heavily now and the fronts
> don't lock up as easily.
>
> I've thought of stuck/failing calipers, but it's weird both in the
> front would fail at once, the brake fluid is clear with no debris, even
> coming out of each of the calipers on the front. So I would thinking
> combination/proportioning valve problem with the lack of rear pressure,
> but even at that there shouldn't be a constant slight pressure on the
> fronts. The vacuum boost assist seems to work well, but the overall
> pedal pressure is lower than I'd expect. My proportioning valve has a
> bleeder on it and bleeding this a half dozen to a dozen times you can
> get pressure to the rear for one pedal press. Perhaps there's air in
> the rear lines or break I'm missing? But I don't lose fluid and see no
> leaks, and it seems strange I have to bleed a dozen times to move the
> valve enough to get even a little pressure to the rears.
>
> The basic system is two lines off the master cylinder into the
> proporitioning valve, and then they each have splitters to feed
> left/right of rear or front.
>
> Any help would be appreciated, I'm not really sure what to try short of
> replacing the master cylinder and maybe the booster to be sure, but
> that's an expensive proposition, even a test to prove the master was
> bad would be useful.
>
> Thanks,
> Chris
>
>



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No, the fluid is clear and free of debris. Not discolored at all,
perfectly clear, same as from the bottle new. I don't see how other
lines would contaminate it, but along those thoughts I should mention
that I have a power assisted clutch that while using a secondary
cylinder pulls from the same resevoir as the brakes.

Thanks, Chris

Try loosening a bleeder on the front caliper, see if the brake frees up, if
so you can keep backing up the line( when the condition is there of course)
loosening a line at certain junctions until you locate where the pressure is
coming from. Also check for free play in the pedal, should be about 1/8 to
1/4 ".
> wrote in message
oups.com...
>
> No, the fluid is clear and free of debris. Not discolored at all,
> perfectly clear, same as from the bottle new. I don't see how other
> lines would contaminate it, but along those thoughts I should mention
> that I have a power assisted clutch that while using a secondary
> cylinder pulls from the same resevoir as the brakes.
>
> Thanks, Chris
>
>



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Yeah there is a fair amount of free play, if by that you mean movement
of pedal before brakes engage. I'd say over an inch, but it's hard to
tell, and it's hard to notice them when they start to engage, it seems
they go from nothing to fairly hard. The boost seems to be working
though, I pump up and when you start the car the pedal pulls down.

Thanks,
Chris

Sounds like a leaking check valve in the master cylinder.

--
Message posted via http://www.carkb.com

Well, not sure yet if there's something more serious like a check valve
or whatnot, but I did solve most of the problem. My car has been
mostly sitting unused for 2 years or so, and while the body didn't rust
at all, the brakes must have. The pads rid on metal and are compressed
by the caliper piston, as far as I can tell they release by just
friction of the pads and lack of resistance, or less from the caliper.
My pads were rusted completely solid to the metal arms they ride in,
some I had to pry off. After cleaning them and putting a dab of
lubricant they now 'can' release.

Doing this 2 wheels freed up instantly and work as their suppose to. 2
others felt like they were dragging worse. One of these was fixed with
a simple bleed, the other's bleeder broke when I tried to open it, but
that caliper looked very bad anyway. So, we'll see once that caliper's
in and the system is rebled where I am at. I really hope this is the
problem and not just a secondary problem caused my extra pressure from
a messed up regulator or master cylinder.

Thanks for the suggestions,
Chris