C4 w/ Hissing Brakes

'92 Auto

The pedal has recently began to feel hard and i have noticed a hissing
sound coming from under the foot well when applying pressure to the
pedal. My guess is that a seal in the booster is leaking, but into the
foot well? This a complete booster replacement or a 3 dollar seal?

Anyone else experienced this?

Also, in the past I have had a few brake failures after decenting down
VERY steep hills. The brakes worked fine on the hills but after getting
onto level pavement, the brakes COMPLETELY failed to work. After a bit
of pumping they came back to life and worked PERFECTLY fine for YEARS.
WTF? Was unable to trace that problem for obvious reasons but now I DO
have a problem.

TIA

I can't offer any suggestions, but, let me see if I understand this. You
had the brakes "COMPLETELY" fail and because they came back after pumping
you didn't do anything for "YEARS?" Even with my limited mechanical
knowledge that sounds like an accident waiting to happen,.even if you had
difficulty tracing the problem.
Rob

"Sacre Bleu" > wrote in message
...
> '92 Auto
>
> The pedal has recently began to feel hard and i have noticed a hissing
> sound coming from under the foot well when applying pressure to the
> pedal. My guess is that a seal in the booster is leaking, but into the
> foot well? This a complete booster replacement or a 3 dollar seal?
>
> Anyone else experienced this?
>
> Also, in the past I have had a few brake failures after decenting down
> VERY steep hills. The brakes worked fine on the hills but after getting
> onto level pavement, the brakes COMPLETELY failed to work. After a bit of
> pumping they came back to life and worked PERFECTLY fine for YEARS.
> WTF? Was unable to trace that problem for obvious reasons but now I DO
> have a problem.
>
> TIA

Scubabix wrote:

> I can't offer any suggestions, but, let me see if I understand this. You
> had the brakes "COMPLETELY" fail and because they came back after pumping
> you didn't do anything for "YEARS?" Even with my limited mechanical
> knowledge that sounds like an accident waiting to happen,.even if you had
> difficulty tracing the problem.
> Rob

Like I said, the problem could not be isolated. Everything was
functioning correctly ie. no mechanical or error code conflicts.
2 different mechanics, $500 later, nada.

I should have fixed the problem by unloading the car as this has been
the absolute worst car I have ever owned with regards to reliability.

Sacre Bleu wrote:

> '92 Auto
>
> The pedal has recently began to feel hard and i have noticed a hissing
> sound coming from under the foot well when applying pressure to the
> pedal. My guess is that a seal in the booster is leaking, but into the
> foot well? This a complete booster replacement or a 3 dollar seal?
>
> Anyone else experienced this?
>
> Also, in the past I have had a few brake failures after decenting down
> VERY steep hills. The brakes worked fine on the hills but after getting
> onto level pavement, the brakes COMPLETELY failed to work. After a bit
> of pumping they came back to life and worked PERFECTLY fine for YEARS.
> WTF? Was unable to trace that problem for obvious reasons but now I DO
> have a problem.
>
> TIA

I also need to add that when idling in park, depressing the brake pedal
also bumps the idle speed up about 300 RPMs.

If the idle is going up, then it sounds like stepping on the brake
introduces a new air path. In other words, the booster is leaking and
letting air in.

Descending down the hills could have simply overheated the brakes, not
knowing exactly how steep, what speeds, and how much braking. That could
have boiled the fluid, which once cooling on the flatlands would have
retracted back into the MC and basically left a gap in the hydraulic link
(big air bubble in the lines, calipers, or even MC). Pumping them got the
air bubble moved to either someplace that lets the brakes work or maybe even
out.

Either way, after boiling the fluid, the temperature at which it will boil
again is MUCH lower, and should be flushed out and replaced immediately.

Suggestion: 1. replace booster (or repair if you know how) 2. flush brake
fluid completely

"Sacre Bleu" > wrote in message
...
> Sacre Bleu wrote:
>
>> '92 Auto
>>
>> The pedal has recently began to feel hard and i have noticed a hissing
>> sound coming from under the foot well when applying pressure to the
>> pedal. My guess is that a seal in the booster is leaking, but into the
>> foot well? This a complete booster replacement or a 3 dollar seal?
>>
>> Anyone else experienced this?
>>
>> Also, in the past I have had a few brake failures after decenting down
>> VERY steep hills. The brakes worked fine on the hills but after getting
>> onto level pavement, the brakes COMPLETELY failed to work. After a bit of
>> pumping they came back to life and worked PERFECTLY fine for YEARS.
>> WTF? Was unable to trace that problem for obvious reasons but now I DO
>> have a problem.
>>
>> TIA
>
> I also need to add that when idling in park, depressing the brake pedal
> also bumps the idle speed up about 300 RPMs.

Tom in Missouri wrote:

> If the idle is going up, then it sounds like stepping on the brake
> introduces a new air path. In other words, the booster is leaking and
> letting air in.

That's what I thought as well, a slightly ruptured diaphram/rear seal.
I only hear the hissing inside the foot well. Don't hear it in the
engine compartment.

>
> Descending down the hills could have simply overheated the brakes, not
> knowing exactly how steep, what speeds, and how much braking. That could
> have boiled the fluid, which once cooling on the flatlands would have
> retracted back into the MC and basically left a gap in the hydraulic link
> (big air bubble in the lines, calipers, or even MC). Pumping them got the
> air bubble moved to either someplace that lets the brakes work or maybe even
> out.

It was a detour that I had to take a few times, about a 9 mile very
steep road. No high speeds, LOTS of hairpins. But I do recall a slight
'pad burn' smell 2/3rds down the hill, which would explain overheated
fluid theory. So even after purging the fluids, this situation could
potentially happen again! Could it be that I'm running cheap brake
pads that generate more heat than better quality pads? I do recall
possibly installing 'cheaper' pads the last time i did the brakes.
Huuuuummmm....

> Either way, after boiling the fluid, the temperature at which it will boil
> again is MUCH lower, and should be flushed out and replaced immediately.
>
> Suggestion: 1. replace booster (or repair if you know how) 2. flush brake
> fluid completely

Thanks for the suggestions! I think you nailed it.

I'm guessing I'll need to flush/bleed the line from the MC to the
Modulator first. Then flush/bleed each caliper afterward, doing one axle
at a time, right? I've noticed that a pressurizer is commonly used on
the MC to bleed the system. Is this better than pedal-pumping?
Any other comments on possible snafus is greatly appreciated!
I've never done this to a car with ABS.

Many thanks!

Jacques

I agree with Tom in Missouri about potential boiling fluid - especially
if the fluid is old. Once the fluid absorbs water (normal with age)
it'll boil at even lower temperatures.

As for the hissing, it's a seal in the booster. And if it's anything
like my car, it'll get a lot worse fast.

I've searched all the obvious places for a replacement seal but I think
we're stuck with replacing the whole thing. UPS delivered an Autozone
rebuilt replacement this morning for $100 + $18 core. Autozone will
surely take my $18 core, replace the $3 seal, and sell it to someone
else for $100.

btw, it's a pretty normal problem. I've had boosters of all makes
start leaking like that. Don't get mad at your Corvette.

-rev




Sacre Bleu wrote:
> '92 Auto
>
> The pedal has recently began to feel hard and i have noticed a hissing
> sound coming from under the foot well when applying pressure to the
> pedal. My guess is that a seal in the booster is leaking, but into the
> foot well? This a complete booster replacement or a 3 dollar seal?
>
> Anyone else experienced this?
>
> Also, in the past I have had a few brake failures after decenting down
> VERY steep hills. The brakes worked fine on the hills but after getting
> onto level pavement, the brakes COMPLETELY failed to work. After a bit
> of pumping they came back to life and worked PERFECTLY fine for YEARS.
> WTF? Was unable to trace that problem for obvious reasons but now I DO
> have a problem.
>
> TIA

I had the same sort of problem with my 93, it was the booster. After you
take it out, you will see why you might only hear inside the car and not
from the engine compartment. I was lucky enough to find a good used one
since everyone from the dealers to the parts stores had them back-ordered.
I went ahead and replaced the master cylinder while I was at it. I usually
try and do things that I might have to take apart a second time. Also
completely drained the fluid and replaced it. What I did was get it close
and then took it to a shop to have them bleed it the rest of the way.

"Sacre Bleu" > wrote in message
...
> Tom in Missouri wrote:
>
>> If the idle is going up, then it sounds like stepping on the brake
>> introduces a new air path. In other words, the booster is leaking and
>> letting air in.
>
> That's what I thought as well, a slightly ruptured diaphram/rear seal.
> I only hear the hissing inside the foot well. Don't hear it in the
> engine compartment.
>
>>
>> Descending down the hills could have simply overheated the brakes, not
>> knowing exactly how steep, what speeds, and how much braking. That could
>> have boiled the fluid, which once cooling on the flatlands would have
>> retracted back into the MC and basically left a gap in the hydraulic link
>> (big air bubble in the lines, calipers, or even MC). Pumping them got
>> the air bubble moved to either someplace that lets the brakes work or
>> maybe even out.
>
> It was a detour that I had to take a few times, about a 9 mile very
> steep road. No high speeds, LOTS of hairpins. But I do recall a slight
> 'pad burn' smell 2/3rds down the hill, which would explain overheated
> fluid theory. So even after purging the fluids, this situation could
> potentially happen again! Could it be that I'm running cheap brake
> pads that generate more heat than better quality pads? I do recall
> possibly installing 'cheaper' pads the last time i did the brakes.
> Huuuuummmm....
>
>> Either way, after boiling the fluid, the temperature at which it will
>> boil again is MUCH lower, and should be flushed out and replaced
>> immediately.
>>
>> Suggestion: 1. replace booster (or repair if you know how) 2. flush
>> brake fluid completely
>
> Thanks for the suggestions! I think you nailed it.
>
> I'm guessing I'll need to flush/bleed the line from the MC to the
> Modulator first. Then flush/bleed each caliper afterward, doing one axle
> at a time, right? I've noticed that a pressurizer is commonly used on
> the MC to bleed the system. Is this better than pedal-pumping?
> Any other comments on possible snafus is greatly appreciated!
> I've never done this to a car with ABS.
>
> Many thanks!
>
> Jacques

The Reverend Natural Light wrote:

> I agree with Tom in Missouri about potential boiling fluid - especially
> if the fluid is old. Once the fluid absorbs water (normal with age)
> it'll boil at even lower temperatures.
>
> As for the hissing, it's a seal in the booster. And if it's anything
> like my car, it'll get a lot worse fast.
>
> I've searched all the obvious places for a replacement seal but I think
> we're stuck with replacing the whole thing. UPS delivered an Autozone
> rebuilt replacement this morning for $100 + $18 core. Autozone will
> surely take my $18 core, replace the $3 seal, and sell it to someone
> else for $100.
>
> btw, it's a pretty normal problem. I've had boosters of all makes
> start leaking like that. Don't get mad at your Corvette.
>

Yeah, replacing the whole thing is the way to go.
$140+core out here in Los Angeles. Is yours plastic?

Also, have you pulled your booster yet?
I noticed that support strut that crosses in front of the booster.
Did you have to remove it? Looks like a pain! Also, is there enough
slack in the lines going to the MC to allow it to be moved out of the
way? Not sure if I want to do the MC at the same time.

Thanks for you input!

Jacques

Yes to removing the bracket, but the hard part is under the dash.

"Sacre Bleu" > wrote in message
...
> The Reverend Natural Light wrote:
>
>> I agree with Tom in Missouri about potential boiling fluid - especially
>> if the fluid is old. Once the fluid absorbs water (normal with age)
>> it'll boil at even lower temperatures.
>>
>> As for the hissing, it's a seal in the booster. And if it's anything
>> like my car, it'll get a lot worse fast.
>>
>> I've searched all the obvious places for a replacement seal but I think
>> we're stuck with replacing the whole thing. UPS delivered an Autozone
>> rebuilt replacement this morning for $100 + $18 core. Autozone will
>> surely take my $18 core, replace the $3 seal, and sell it to someone
>> else for $100.
>>
>> btw, it's a pretty normal problem. I've had boosters of all makes
>> start leaking like that. Don't get mad at your Corvette.
>>
>
> Yeah, replacing the whole thing is the way to go.
> $140+core out here in Los Angeles. Is yours plastic?
>
> Also, have you pulled your booster yet?
> I noticed that support strut that crosses in front of the booster.
> Did you have to remove it? Looks like a pain! Also, is there enough
> slack in the lines going to the MC to allow it to be moved out of the
> way? Not sure if I want to do the MC at the same time.
>
> Thanks for you input!
>
> Jacques