Hi Group, I have a question in regards to the brake pedal on my 97 Civic. It
has front disc, and rear drums. I have had the car for six months now, and
the brake pedal has always been low. It stops just about an inch or two
above the floor. The pedal is not spongy, I have bleed the hell out of it,
has at least 50% left of pads and shoes, I even replaced the master
cylinder. The flex lines are good, no expansion. The brakes work fine, it
just has a very low pedal. If anyone can shed some light on this, I would
really appreciate it.
are the brake drums self-adjusting properly? can you hear them click
when you back them off, then pump with the brake pedal?
if you replaced the master cylinder, is the travel the same as it was
there shouldn't be any drag on the drum when properly adjusted. if the
threads on the adjuster screw are rusted or even greased, they can fail
to self-adjust. i recommend removal, cleaning, refitting, then checking
to check operation, reassemble screwed all the way in, then when
reassembled, press on the brake pedal 20 times. each time you release,
you should hear the self-adjuster click. then remove the drum again and
be sure you can see the adjuster has screwed itself out a few mm. if it
has, reassemble and pump the pedal until the clicking stops. you then
should be good. if not, you need to clean and reassemble again. no grease.
what is the pedal travel before engagement?
A low pedal is indicative of several problems, which may or may not be
present in combination:
1) aftermarket pads (wrong friction-coefficient for your brakes);
2) pads not floating freely on their mount brackets;
3) calipers not floating freely on their pins;
4) one or more hydraulic pistons sticking in their bores;
5) rust buildup between caliper, pads, and squeal-shims;
6) persistent air bubble (usually in caliper);
7) misadjusted master cylinder pushrod.
Complete removal of air from the calipers is sometimes only possible by
using the "turn and tap" method, with the caliper off the rotor. This
usually only affects rear calipers though, which you don't have.
If you're looking for a "magic bullet" fix, you probably won't find one.
Your brakes need a good going-over by someone who understands how brakes
while you are correct in theory on #7, it's almost never seen in
practice and i personally think it inviting trouble to cite it as a
cause. unless something is broken, which is not a calibration problem,
the position on the original master cylinder never changes. and if the
master cylinder is replaced with the correct one, the new one is the
same also. imo, this should /not/ be on the list of "diy likely causes".
disagree. for straight replacement with the same master cylinder with
the same part number, the internals are all identical. if they are
identical, there is no reason to adjust the pushrod because the power
servo doesn't change and neither does the pedal lever. the only
possible reason to change the length of the pushrod is if the master
cylinder internals are different [using a different cylinder] or if the
pedal pivots are worn. if the latter, they should be replaced - the
push rod should not be monkeyed with to compensate.
not through anything other than extreme wear or use of an
incorrect/non-standard part. if the former, the parts should be replaced.
indeed, but with the above proviso.
we have seen the result of this here before - if people monkey with the
pedal adjust, they can end up with the cylinder vent holes closed and
the brakes come on as the system warms and expands. that is a serious
Provision for adjustment is built-in to the booster/MC connection for
the single and sole purpose of matching two individual components that
must work together precisely. Much like the throttle body and the
Throttle Position Sensor.
This adjustment is necessary on account of manufacturing tolerances.
If you install a replacement MC (OEM or not), you MUST make sure the
pushrod adjustment is correct.
Pedal height adjust is different from MC pushrod adjust.
indeed, and like the tps, it requires no further attention unless worn.
and the only things that can wear are pivots/contact points, not the
internals of the master cylinder.
absolutely, but that variance is in the pedal/welding, not the
piston/cylinder assembly which is highly precise.
dude, with respect, every single master cylinder i have ever replaced
[and there have been many] - with conforming oem - has had the resultant
pedal travel be precisely as it was before - not surprising since
hydraulic pistons don't wear.
really, if you have experienced difference between pistons, there has to
be some kind of issue, it's not a simple adjustment thing.
height is a function of the stop tab. pushrod adjusts travel, and thus
depression before the equalization valves are closed.
then there is something seriously wrong with your car dude. you need to
fix the cause, not monkey with the symptoms. master cylinder brake
pistons do not wear. once set, you do not need to "adjust" them.
no dude - there is ZERO human factor in their manufacture. these are
all produced by highly consistent and accurate computerized machines.
every single piston has consistency and accuracy you can't even
/contemplate/ with your foot.
oh, busted, dang-it. i confess grumpy, i've never touched a car or a
braking system in my life. i have no clue about manufacturing or
measuring tolerances either. and i know absolutely ZIPPO about hydraulics.
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