soft/low pedal when brake heats up
Ming Yu Yao
(75% left).
After the brake heats up in stop-and-go traffic (in hot weather), the
pedal becomes
soft and goes lower than usual, though I don't feel any obvious
difficult to stop
the car. After the brake cools down, it becomes normal. I have taken the
car to
two different garages and asked if I needed to have the brake fluid
flushed. One
mechanic said brake fluid needed to be flushed only if the caliper
needed to be
changed. The caliper on my car was fine so there was no need to flush
the brake
system. The other mechanic also inspected the brakes and said he didn't
see any
need to flush the brake system.
I bought the car about 4 years ago with 55k miles on it. So, I don't
believe
the brake fluid has ever been bleeded.
Should I go ahead flushing the fluid or is there anything else that
causes
the problem?
Thanks,
Arthur Russell
the head of repeated braking, displacing some brake fluid so that more
pedal travel is required)
You should have your brake fluid flushed...it isn't expensive. Also,
when was the last time the fluid was flushed? Spec service interval is
(at least) every two years.
By the way, since I've responded, I feel obligated to say that this is a
potentially dangerous situation, and I would strongly recommend that you
get if fixed as soon as you possibly can (even if it doesn't turn out to
be moisture in the fluid) The concern is that if the problem gets worse,
you may be in a situation where the pedal goes to the floor without
providing sufficient braking action (so you could hurt someone or get
hurt yourself). Additionally, this kind of problem can have a "run-away"
effect - that is, you use the brakes, which heats the fluid, which boils
some water, which expands the volume taken by the fluid, which tends to
actuate the brakes (even though you aren't pushing on the pedal anymore)
which heats further, which boils more water out etc. A common side
effect of this scenario is noticing that your brakes are
dragging...sometimes even to the point that the car won't move.
Good luck,
-Arthur
Yip Yu
at once.
Yip
pbuck
> 92 Integra with 85K miles, both front and rear disc brakes fairly new
> (75% left).After the brake heats up in stop-and-go traffic (in hot
> weather), the
> pedal becomes soft and goes lower than usual, though I don't feel any
> obvious
> difficult to stop the car. After the brake cools down, it becomes normal.
> I have taken the
> car to two different garages and asked if I needed to have the brake fluid
>
> flushed. One mechanic said brake fluid needed to be flushed only if the
> caliper
> needed to be changed. The caliper on my car was fine so there was no need
> to flush
> the brake system. The other mechanic also inspected the brakes and said he
> didn't
> see any need to flush the brake system.
>
> Should I go ahead flushing the fluid or is there anything else that
> causes the problem?
> Thanks,
Have a 91 Integra, non ABS, 69k miles. Had similar problem, I described it
as "pedal fade" and it was particularly noticeable after driving awhile and
then waiting at a light on slight incline. Went to Acura dealer, Jap car
fix-it garage and a brake shop. All 3 said "master cylinder." 1st two I
expected would tell me something like this, ratrher than simply replace
brake fluid. Brake shop guy I trust as unbiased, he bought OEM master
cylinder and charged me his cost ($187.oo) and installed for what Acura
would charge just for the master at retail cost! Car stops and stays put
now. Fluid replacement is obviously cheaper than master replacement, but
you could have same problem as me. btw, get DOT4 fluid. It has abt 50
degrees higher boiling point than DOT3. Valvoline has it under their
"Synpower" brand and it shows 500+ boiling point vs Castrol at abt 460, got
it at PepBoys.
Keith Broughton
>believe
>the brake fluid has ever been bleeded.
Definately change the brake fluid.
I don't know if it will solve your problem but it should be changed more
often and it's a good starting point for trouble shootong your problem.
Michael Wright
changed the master cylinder and its fine now. Buy a Honda replacement
cylinder, it was about $30 more than a rebuild.
George Macdonald
have tried the same "test" in the same or other Honda products.
I have an '92 Integra GS with similar symptom - I first noticed on a very
hot day in stop-n-go freeway traffic. To be specific the pedal doesn't go
all the way to the floor under these conditions but it gradually sinks
close to the floor as you keep pressure on it and the brakes always work
fine otherwise. There has never been any question of the brakes failing to
stop the car, even in the above-mentioned stop-n-go situation... just that
when stopped I noticed that keeping pressure on the pedal makes it sink
lower and lower. I'd always changed the brake fluid at intervals even
shorter than the scheduled maintenance because of worries about ABS
replacement costs. To elaborate a little further, this require more pedal
pressure (not exceesive though) than would be required to stop the car and
as the pedal sinks it has a springy feel to it... feels like a rubber brake
hose ballooning because of the heat. I've also tried the same test when
the car is cool and there is some sinking of the pedal but not as much.
Now the rub: my '99 Integra GS... because I'd noticed the above oddity I
did the same test with the new car the first time we had a hot day and it
behaves similarly - keep your foot on the brake pedal while stopped in hot
weather and it sinks gradually down close to the floor (not sure it goes
quite as low as the older car but it's difficult to be precise) and has a
springy feel to it. IOW I think it's an idiosynchracy of the system and
nothing to worry about, as long as the brakes work OK in all other
situations. If you have doubts about the freshness of your brake fluid go
ahead and change it anyway - it should be done every 30K miles or so
anyway. If you really want to, change the master cylinder at the same time
but I can assure you it will make little difference. Hell, if you want to
be sure go to a dealer and ask for a test drive of a new car.
On Fri, 25 Aug 2000 09:02:01 -0400, Ming Yu Yao <my...@cisco.com> wrote:
>92 Integra with 85K miles, both front and rear disc brakes fairly new
>(75% left).
>After the brake heats up in stop-and-go traffic (in hot weather), the
>pedal becomes
>soft and goes lower than usual, though I don't feel any obvious
>difficult to stop
>the car. After the brake cools down, it becomes normal. I have taken the
>car to
>two different garages and asked if I needed to have the brake fluid
>flushed. One
>mechanic said brake fluid needed to be flushed only if the caliper
>needed to be
>changed. The caliper on my car was fine so there was no need to flush
>the brake
>system. The other mechanic also inspected the brakes and said he didn't
>see any
>need to flush the brake system.
>
>I bought the car about 4 years ago with 55k miles on it. So, I don't
>believe
>the brake fluid has ever been bleeded.
>
>Should I go ahead flushing the fluid or is there anything else that
>causes
>the problem?
>
>Thanks,
>
>
>
Rgds, George Macdonald
"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??
Abey Joseph
had the rotors, pads and shoes replaced. Also had the front calipers
replaced as well. The brake fluid in the car was flushed and replaced
with DOT3 fluid. The symptoms you mention point to the master
cylinder! I replaced the master cylinder and haven't had that problem
since. Good Luck.
Abey.
"Ming Yu Yao" <my...@cisco.com> wrote in message
news:39A66E49...@cisco.com...
Ming Yu Yao
yesterday morning. The brake system was inspected again and still no
problem could be found. The mechanic finally suggested to change
the "master cylinder", but he really was not sure as he was not able
to reproduce soft/low pedal in his test drive, and so he could not
guarantee the problem would go away with the change of the "master
cylinder". As maintenance and start point for trouble shooting, I asked
him to flush the brake system and he did it. Yesterday afternoon, it
happened to be very hot, so I drove the car around for about 30 miles
in town and really stressed the brake hard. I didn't feel soft/low
pedal anymore. Hope the problem has been fixed by the fluid change.
I will continue to watch it out though.
Thanks again!
Ming
Arthur Russell
Camry and 91 Accord) and a sinking pedal was both something to watch
for, and something I did not experience. Why was I running such a test?
On the Rabbit, I was having vacuum booster problems, and so the same
test was used for different reasons. On the other two cars, I was only
testing the booster performance (testing for leaking at various push-rod
positions) Again, I never experienced a sinking pedal, in fact, in the
Rabbit before the booster replacement, the pedal would raise a bit as
the vacuum leaked past the pushrod)
The fact that hot brakes makes a difference is also pretty
incriminating! I would encourage folks to consider that a sinking brake
pedal is a big deal. As an acid test, one can disconnect the vacuum line
from the booster to get a very clear idea of how the hydraulics are
working without the booster "disconnecting" your foot from the
hydraulic. A sinking pedal in this case means fluid is escaping from the
pressurized part of the system (past a seal, or through a crack etc.) or
that the volume of the system is not fixed (expanding brake hose etc.)
Neither scenario is consistent with reliable brakes!
-Arthur
George Macdonald
wrote:
>I've actually done the test. I have done it in a few cars (81 Rabbit, 88
>Camry and 91 Accord) and a sinking pedal was both something to watch
>for, and something I did not experience. Why was I running such a test?
>On the Rabbit, I was having vacuum booster problems, and so the same
>test was used for different reasons. On the other two cars, I was only
>testing the booster performance (testing for leaking at various push-rod
>positions) Again, I never experienced a sinking pedal, in fact, in the
>Rabbit before the booster replacement, the pedal would raise a bit as
>the vacuum leaked past the pushrod)
Do any of these cars have ABS? Obviously the VW and the Toyota are not
"similar Honda products" and have zero relevance here... whether the '91
Accord is similar enough I don't know. I'll be doing the same test on a
new Accord EX soon when it arrives so I'll have another reference point.
>The fact that hot brakes makes a difference is also pretty
>incriminating! I would encourage folks to consider that a sinking brake
>pedal is a big deal. As an acid test, one can disconnect the vacuum line
>from the booster to get a very clear idea of how the hydraulics are
>working without the booster "disconnecting" your foot from the
>hydraulic. A sinking pedal in this case means fluid is escaping from the
>pressurized part of the system (past a seal, or through a crack etc.) or
>that the volume of the system is not fixed (expanding brake hose etc.)
>Neither scenario is consistent with reliable brakes!
With the engine off and no vacuum left in the system, the pedal does not
sink and feels nice and firm. Under the conditions of "sinking", in my
case anyway, the pedal never reaches the floor and the pressure on the
pedal is way more than required to stop the car. As already stated, it
does feel like a slightly ballooning rubber brake hose or... the original
poster did not state the model, or whether the car had ABS but I wonder if,
in my case, it might be the high pressures working against the solenoid
springs in the ABS modulator.
At any rate, I have checked that a similar brand new car *does* exhibit
similar behavior. In all other brake inspection tests and in actual use
the brakes on both cars behave normally and are reliable. If you find it a
"big deal" maybe you'll want to investigate further - personally I'm
satisfied that there is no major fault with my cars. Maybe the other
poster's problem is a different one, hard to tell.
>-Arthur
RM
>At any rate, I have checked that a similar brand new car *does* exhibit
>similar behavior. In all other brake inspection tests and in actual use
>the brakes on both cars behave normally and are reliable. If you find it a
>"big deal" maybe you'll want to investigate further - personally I'm
>satisfied that there is no major fault with my cars. Maybe the other
>poster's problem is a different one, hard to tell.
Had the same problem on my 92 Accord EX (with ABS). I was _sure_ it
was the master cylinder. First I flushed the brake fluid and the
problem went away.
when the master cylinder completely fails on a Honda (like it did on
my 90 Accord), typically you feel a clunk in the pedal when the
primary piston bottoms out on the secondary piston inside the master
cylinder. This clunking means you've lost pressure in 1/2 of your
braking system.
My guess on this soft pedal problem is that it's some combination of
wet fluid and a weak master cylinder. Another possible issue is
whether the old rubber brake hoses are a problem.....
Arthur Russell
George Macdonald wrote:
>
> On Mon, 28 Aug 2000 13:20:03 -0400, Arthur Russell <arus...@NOSPAMpaw.com>
> wrote:
>
> >I've actually done the test. I have done it in a few cars (81 Rabbit, 88
> >Camry and 91 Accord) and a sinking pedal was both something to watch
> >for, and something I did not experience. Why was I running such a test?
> >On the Rabbit, I was having vacuum booster problems, and so the same
> >test was used for different reasons. On the other two cars, I was only
> >testing the booster performance (testing for leaking at various push-rod
> >positions) Again, I never experienced a sinking pedal, in fact, in the
> >Rabbit before the booster replacement, the pedal would raise a bit as
> >the vacuum leaked past the pushrod)
>
> Do any of these cars have ABS? Obviously the VW and the Toyota are not
> "similar Honda products" and have zero relevance here... whether the '91
> Accord is similar enough I don't know. I'll be doing the same test on a
> new Accord EX soon when it arrives so I'll have another reference point.
None had ABS. As far as the relevance argument is concerned, I would say
that they are similar enough in that the cars I was using as comparison
have exactly the same basic design as the one in question. Even if the
poster's Integra had ABS, it didn't sound like they were doing anything
which would cause the modulator to go active. In that case, the volume
of the pressurized system wouldn't be changing on them. Additionally, if
there were differences between the Acura and Honda lineup for braking
feel, without any data at all, I would guess that the Acura would have
the stiffer braking components since they seem to be toted as sportier
than the Honda counterpart. I'd bet lots of the parts like brake hoses
are made by the same manufacturer though, for cost reasons.
> >The fact that hot brakes makes a difference is also pretty
> >incriminating! I would encourage folks to consider that a sinking brake
> >pedal is a big deal. As an acid test, one can disconnect the vacuum line
> >from the booster to get a very clear idea of how the hydraulics are
> >working without the booster "disconnecting" your foot from the
> >hydraulic. A sinking pedal in this case means fluid is escaping from the
> >pressurized part of the system (past a seal, or through a crack etc.) or
> >that the volume of the system is not fixed (expanding brake hose etc.)
> >Neither scenario is consistent with reliable brakes!
>
> With the engine off and no vacuum left in the system, the pedal does not
> sink and feels nice and firm. Under the conditions of "sinking", in my
> case anyway, the pedal never reaches the floor and the pressure on the
> pedal is way more than required to stop the car. As already stated, it
> does feel like a slightly ballooning rubber brake hose or... the original
> poster did not state the model, or whether the car had ABS but I wonder if,
> in my case, it might be the high pressures working against the solenoid
> springs in the ABS modulator.
I think the original poster said the model was an Integra.
> At any rate, I have checked that a similar brand new car *does* exhibit
> similar behavior. In all other brake inspection tests and in actual use
> the brakes on both cars behave normally and are reliable. If you find it a
> "big deal" maybe you'll want to investigate further - personally I'm
> satisfied that there is no major fault with my cars. Maybe the other
> poster's problem is a different one, hard to tell.
>
> >-Arthur
Wait a second here, I can't believe you are mentioning "a similar brand
car" while you just discounted the anecdotal story I had about my own
Honda! Come on, my advice was sound, I think. And you know, I could have
easily been wrong and it could have been some brake hose expanding
within specs, but in this case I turned out to be right (see poster's
second follow-up) In my opinion, the point here is that a Honda owner
now has a car that was safer than it was the other day, and that is
good.
-Arthur
George Macdonald
wrote:
>See responses interleaved below please.
>
>George Macdonald wrote:
>>
>> On Mon, 28 Aug 2000 13:20:03 -0400, Arthur Russell <arus...@NOSPAMpaw.com>
>> wrote:
>>
>> >I've actually done the test. I have done it in a few cars (81 Rabbit, 88
>> >Camry and 91 Accord) and a sinking pedal was both something to watch
>> >for, and something I did not experience. Why was I running such a test?
>> >On the Rabbit, I was having vacuum booster problems, and so the same
>> >test was used for different reasons. On the other two cars, I was only
>> >testing the booster performance (testing for leaking at various push-rod
>> >positions) Again, I never experienced a sinking pedal, in fact, in the
>> >Rabbit before the booster replacement, the pedal would raise a bit as
>> >the vacuum leaked past the pushrod)
>>
>> Do any of these cars have ABS? Obviously the VW and the Toyota are not
>> "similar Honda products" and have zero relevance here... whether the '91
>> Accord is similar enough I don't know. I'll be doing the same test on a
>> new Accord EX soon when it arrives so I'll have another reference point.
>
>
>None had ABS. As far as the relevance argument is concerned, I would say
>that they are similar enough in that the cars I was using as comparison
>have exactly the same basic design as the one in question. Even if the
>poster's Integra had ABS, it didn't sound like they were doing anything
>which would cause the modulator to go active.
I'm not talking about the modulator going active - look at how it works.
> In that case, the volume
>of the pressurized system wouldn't be changing on them. Additionally, if
>there were differences between the Acura and Honda lineup for braking
>feel, without any data at all, I would guess that the Acura would have
>the stiffer braking components since they seem to be toted as sportier
>than the Honda counterpart. I'd bet lots of the parts like brake hoses
>are made by the same manufacturer though, for cost reasons.
>
>
>> >The fact that hot brakes makes a difference is also pretty
>> >incriminating! I would encourage folks to consider that a sinking brake
>> >pedal is a big deal. As an acid test, one can disconnect the vacuum line
>> >from the booster to get a very clear idea of how the hydraulics are
>> >working without the booster "disconnecting" your foot from the
>> >hydraulic. A sinking pedal in this case means fluid is escaping from the
>> >pressurized part of the system (past a seal, or through a crack etc.) or
>> >that the volume of the system is not fixed (expanding brake hose etc.)
>> >Neither scenario is consistent with reliable brakes!
>>
>> With the engine off and no vacuum left in the system, the pedal does not
>> sink and feels nice and firm. Under the conditions of "sinking", in my
>> case anyway, the pedal never reaches the floor and the pressure on the
>> pedal is way more than required to stop the car. As already stated, it
>> does feel like a slightly ballooning rubber brake hose or... the original
>> poster did not state the model, or whether the car had ABS but I wonder if,
>> in my case, it might be the high pressures working against the solenoid
>> springs in the ABS modulator.
>
>
>I think the original poster said the model was an Integra.
Jeez, do I have to spell it out? The Integra GS has ABS, the RS and LS do
not.
>
>> At any rate, I have checked that a similar brand new car *does* exhibit
>> similar behavior. In all other brake inspection tests and in actual use
>> the brakes on both cars behave normally and are reliable. If you find it a
>> "big deal" maybe you'll want to investigate further - personally I'm
>> satisfied that there is no major fault with my cars. Maybe the other
>> poster's problem is a different one, hard to tell.
>>
>> >-Arthur
>
>
>Wait a second here, I can't believe you are mentioning "a similar brand
>car"
You are misreading (and even misquoting) what I said - intentionally I
don't know but I'll repeat what I've already said: the comparison is a '92
Integra GS vs. a '99 Integra GS. IOW it's a brand new car which is
similar... got it?... at least the '99 was close enough to brand new - 6
months and 6K miles - when I did the test.
> while you just discounted the anecdotal story I had about my own
>Honda! Come on, my advice was sound, I think. And you know, I could have
>easily been wrong and it could have been some brake hose expanding
>within specs, but in this case I turned out to be right (see poster's
>second follow-up) In my opinion, the point here is that a Honda owner
>now has a car that was safer than it was the other day, and that is
>good.
Like I already said, maybe we're observing different symptoms. My '99 car
is now at 18K miles and I've just repeated the test and the pedal still
sinks if you keep pressure on it while standing still and it sinks more
when hot... I'm talking about under-hood hot, not brakes hot.
Mike
> Thanks to you all for the info. I brought the car to a third garage
> yesterday morning. The brake system was inspected again and still no
> problem could be found. The mechanic finally suggested to change
> the "master cylinder", but he really was not sure as he was not able
> to reproduce soft/low pedal in his test drive, and so he could not
> guarantee the problem would go away with the change of the "master
> cylinder". As maintenance and start point for trouble shooting, I asked
> him to flush the brake system and he did it. Yesterday afternoon, it
> happened to be very hot, so I drove the car around for about 30 miles
> in town and really stressed the brake hard. I didn't feel soft/low
> pedal anymore. Hope the problem has been fixed by the fluid change.
> I will continue to watch it out though.
>
> Thanks again!
>
> Ming
>
I had a similar problem when my front brake pads were replaced. I suspect
this is due to a badly bled brake system, I wouldn't go round replacing
the master cylinder until I'd flushed the fluid first, which needs to be
done now and again anyway.
Mike.
Lee Cao
"Mike" <sha...@iinet.net.au> wrote in message
news:MPG.141a47eac...@news.iinet.net.au...
> I had a similar problem when my front brake pads were replaced. I suspect
> this is due to a badly bled brake system, I wouldn't go round replacing
> the master cylinder until I'd flushed the fluid first, which needs to be
> done now and again anyway.
Same thing here...
Brake fluid needs to be flushed every 45,000 miles or so. Sooner if you are
really trying to take care of the car. I am going to have my brake fluids
flushed a third time in the upcomming 90,000 mile service.
This one is going to be a dewsey... $$$$$$$$
> Mike.
--
Lee Cao - www.leecao.com
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