Brakes on a 97 Civic

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.

Thanks,
Weldon

 

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
before?

 

Yes, the rear brakes are self adjusting, and they are adjusted properly. The
travel is the same with the new master cylinder.

 

i'll take your word for it, but how do you know? what did you check?

in inches, how much travel before the brakes start to engage?

 

I removed the drums and checked the hardware, and verified the drag on the
drum.

 

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
operation.

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?

 

I have LOTS to say on this one. but don't have the time just now to write
it up.

In short, you have numersous problems.

 

Given that the front disk pads engage the rotors before the rear shoes
engage the drum, and do 70-80% of the stopping, I think I would look
elsewhere besides the rear drums for clues to this issue.

 

actually, that's not true - the rears come on first, but the
proportioning valve applies progressively more to the fronts as the
pedal continues to be pressed.

other than air in the hydraulics, a problem with the hoses or some
serious caliper misalignment, maladjusted rears are the only place where
you can cause this kind of pedal travel.

 

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
work.

 

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".

 

It is _often_ seen when a master cylinder is replaced and the pushrod is
not adjusted to suit.

It is a legitimate cause of a low pedal under certain circumstances.

Given that testing for that involves nothing more than pushing on the pedal
with your fingertips, it's worth checking.

 

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
safety issue.

 

Exactly. I can't even remember the number of times that I've had to
re-adjust the pushrod due to low pedal concerns.

Absolutely. After the usual suspects are eliminated.

What must be remembered here is the human factor involved in cylinder
manufacture/remanufacture. That factor always results in variations...

JT

 

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.

 

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.

 

That's why I listed the MC pushrod LAST in my list.

Perhaps I should have specified that I was listing things in order of
likeliness.

Not just that, but tool variance and wear. Production quantities always
involve some degree of tool wear, which changes dimensions during the run.

 

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.

 

any dimensional differences on hydraulics are measured in hundredths of
mm. that affects pedal travel not even a tiny bit.

 

My experience is on a number AND variety of vehicles. You lose once again.

Then you are seriously out of touch with reality. The above may be the
single most stupid thing you have uttered.

JT