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.
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.
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.
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
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
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
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.
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.
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.
I think if you are running lots of hilly/mountainous country, you can run
some DOT 4 fluid which is a bit higher temperature than the DOT 3. However,
you can find the racing DOT 3 fluids like Wilwood and Motul to get good high
Mercedes also uses a factory higher temperature than standard DOT 3. And
some time back, many ran FORD fluid that was a DOT 4 or so rating.
I don't think the DOT 4 messes with the ABS, but DOT 5 definitely does. DO
NOT run the DOT 5 silicone brake fluid.
The rotors and pads on the C4s had limitations. The rotors were thinner to
be lighter, but they overheat and warp much easier than other years. You
should check on the Vette Net email list www.vettenet.org or Corvette Forum
www.corvetteforum.com for those who have been autocrossing and doing track
events with C4s for recommendations and warnings.
I've never done an ABS Corvette either, so I can't tell you.
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.
Sacre Bleu wrote:
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!
I just finished the job. All things considered, it was quite easy. It
would have really been fun if the girlfriend hadn't dropped by halfway
through, intent on speading her lousy mood.
The nuts under the dash were easy. I used a very long extension
(~24"+) with a u-joint adapter and a 13mm shallow socket for both.
Under the hood, the master cylinder has plenty of slack to swing out of
the way. No need to crack open any brake lines. Swing the ECM out of
the way and unbolt the frame brace. I didn't remove the brace, but
once loose and moved slightly there was room to pull the booster out.
There is one bolt for the brace that is a pain in the ass - you'll know
it when you get to it.
With the booster out, I used a dial caliper, straight edge, needle nose
vice grips, and an 8mm wrench to set the rod depth on the new booster
the same as the old one. The instructions detail how to set it, but I
just made sure it was the same as the old one.
The new booster (autozone.com - $100 +$18 core, free shipping) looks
exactly like the old one. I noticed after installation that the brake
pedal is much lower than it used to be, to the point that I had to
adjust the brake light switch. Perhaps the input rod was supposed to
be adjusted. I like it this way because the brake pedal was so much
higher than the throttle before that there was no hope of a heel-toe
shift. I might be able to do it now.
So, it's one of the easier and cheaper fixes I've had to do so far.
Take your time. Post back if you run into any snags.
Sacre Bleu wrote:
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