Brake Pedal Sinking at the Traffic Lights

Vehicle: 1994 Civic with no ABS

Problem: I am having a weird problem with my brakes. A few days ago, on a
stinking hot day, I was at a set of traffic lights, when suddenly, my brake
pedal began to slowly sink to the floor. The brakes worked fine and would
stop the car, even under severe braking. The only problem would be that the
brakes, when depressed would begin to sink to the floor after a few seconds.

They were fine in the morning and fine in the evening. The only difference
was that when I drove the car during the day, the weather was over 35
degrees C. This problem occurred twice and each time it occurred, it was on
a hot day. As the day became cooler or when the car is driven on a day
below 35 degrees C, the brakes behave normally?

Any ideas?

 

sounds like an old 55 chevy i had back in 1962.. it would stop all the
time, but if you kept your foot on the brake it would go to the floor,,
take foot off the brake and reapply the pedal and it would work fine..
dont remember what we did as i was a kid at the time, teenager, but it
seems that the seals in the mast. cylinder are bad???? just a guess???

 

I'm no expert, but from what I've read here and experienced, It's either
air in the brake lines, or your master cylinder needs to be replaced.. I
had the same problem a while ago on my wife's car... Unfortunately, it
was the more expensive of the two possibilities, master cylinder and two
wheel cylinders..

I think i read it here, but one way to tell if it's one or the other is
if your car is off, and you pump the brakes to where they are hard to
push... then, you hold down on the pedal (like you're stopped at a light)
and if the pedal sinks w/ the car off, it's the mast cyl.

I'm not 100% sure on that, but hopefully someone w/ some knowledge will
agree/disagree with me.

good luck.

--
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town" of the Star Wars Universe!

 

Master cylinder seals are bad. Corrosion in the M/C bore. Need a new or
reman M/C.

 

If the pedal sinks just a little (about an inch) I would not worry
about this - many cars do that to some degree. With the engine NOT
running, pump the brake pedal until you almost cannot push it down,
then with your foot firmly on the pedal start the engine - you will
feel it sinks a little bit. If it's sort of the same you had
experienced - forget about it.

 

Unfortunately, the pedal sinks slowly until it almost hits the firewall.
However, as today is a cool day, the brake pedal is not sinking and the
brakes are working fine. The problem only occurs on a hot day. Bizarre!!

 

This is very typical of ~1994+ Honda master cylinder failures. They
aren't like earlier models or other cars I have had. Those tend to
suddenly break and you know you have a problem. Newer Hondas will be
fine most of the time but occasionally in warm weather the pedal will
sink. It would probably continue like this for a long time but don't
wait to fix it.

 

Melborne,

Whatever you do (or don't do), check your brake fluid reservoir every
day, to make sure you're not losing some of that fluid somewhere (like
into one of the brake drums)

Do the 'lamp test' as well to be sure your dash lights will give you
some warning in advance.... It's in your owner's manual.

'Curly'

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Thanks Curly,

I checked each of the brake bleeding nipples but none of them have any signs
of leakage.

The brake fluid is at the MAX mark and does not seem to be losing any fluid.

How does one do a lamp test? Isn't it a matter of turning the ignition on
and checking that all the dash warning lights come on?

 

I had a problem like that once, a leaking seal in the master brake cylynder.
I don't think I lost any fluid, it would just leak past the plunger that was
supposed to make the pressure to apply to the brakes. I've noticed that some
of my present day cars have a little leak if I sit and play with them long enough,
but if you can consistently get the pedal to the floor I would have it fixed.

 

In addition, you can check to make sure that (while the ignition's on) when
you remove the lid of the master cylinder, the magnetic float in there
actually descends on it stalk, and actually lights the dashboard brake
warning light.

Also: no one has said this outright, but this is (possibly) actually
dangerous. Once the master cylinder starts to fail this way, it is possible
for it to fail completely, at which point you could have diminished braking
action, or none at all!

-Arthur

 

I had this problem earlier this summer.

Turned out to be the master cylinder starting to fail.
Getting it replaced too care of my problem.

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Thanks for the word of caution Arthur,

The weird thing about the brakes on my car is that they have been working
perfectly and have not played up since the day I first entered this original
post. Therefore, it is possible that this has been going on for quite some
time and may continue to do so unless the weather gets very hot.

I called a dealership today and they said that the brakes may need bleeding
Could this be the cause of the problem?

 

No. If they needed bleeding they would be bad all the time. Plus,
the very act of bleeding them may do further damage to the MC.

With cooler weather setting in, you may not notice the problem until
next Spring. I went about two years with this problem - never really
felt dangerous and I forgot all about it October through April. It
was gradually getting worse though. (I would have fixed it sooner but
I wasn't sure of the cause. However, I didn't have a problem all
summer after replacing the MC this Spring.

 

I had the master cylinder fail on my 91 Accord (also no ABS). The symptom
was that on a short trip home, I noticed that when stopping at a light (a
gradual stop, with not too much pedal pressure) the pedal seemed to go
slightly past the point that I was used to. For the next light, I hit it a
bit harder to see what was going on, and it was totally fine. So, I got
home, dropped my wife off, and experimented with it for a minute.

I found that if I pushed gently, I could definitely get the pedal to "slip"
past the usual point where it becomes rock hard. In fact, I found that if I
really feathered around with it, I could almost get it to the floor.
Because the pedal was still solid at the bottom of the travel, there was
almost certainly no air in the lines. I suspected the master cylinder was
failing. The next day my shop confirmed this and replaced it; the problem
was fixed.

Listen, everyone's philosophy differs here. Some folks may make a conscious
decision to drive carefully, or downshift, or be ready with the emergency
brake etc. Other folks, me for example, are pretty anal when it comes to
brakes. I always have the fluid flushed every two years. I never add fluid
- if it's low, the pads are wearing and I see to them, or I find the leak.
Don't just replace pads yourself, take apart the calipers and do the
complete maintenance (lube guide pins, inspect boots etc.) And, if the
master cylinder starts to fail, although the system has two independent
hydraulic circuits, assume that you have just experienced the "first
failure", and the second one will be when you REALLY NEED THE BRAKES TO WORK!

So, please duplicate your problem to a shop that you trust, and have them
fix it. Try the light pressure, slow pedal thing I mentioned. If the shop
determines the cause of the pedal behavior is something
non-life-threatening, like a faulty booster or a little air in the lines,
then chalk it up to being too safety conscious...but I am betting on the
master cylinder, and you need it to be working right.

Good luck,
Arthur

 

Master cylinder. It's bypassing internally, essentially transferring fluid
from one end to the other. Just change it out.


|Vehicle: 1994 Civic with no ABS
|
|Problem: I am having a weird problem with my brakes. A few days ago, on a
|stinking hot day, I was at a set of traffic lights, when suddenly, my brake
|pedal began to slowly sink to the floor. The brakes worked fine and would
|stop the car, even under severe braking. The only problem would be that the
|brakes, when depressed would begin to sink to the floor after a few seconds.
|
|They were fine in the morning and fine in the evening. The only difference
|was that when I drove the car during the day, the weather was over 35
|degrees C. This problem occurred twice and each time it occurred, it was on
|a hot day. As the day became cooler or when the car is driven on a day
|below 35 degrees C, the brakes behave normally?
|
|Any ideas?
|
|
|

Rex in Fort Worth