Hey guys,

Ive finally found the time to discuss and repair what
seems to be a on/off malfunction of my brakes, which
also contributed to a recent traffic ticket ..

Ive never had a problem until I rebuilt the existing engine
and ran a high overlap cam in my L98 car. Lopey idle, moderate
lift, but alot of duration, computer friendly LSA (112)

Vacuum loads possibly low at idle and part throttle,
causing no pedal and a chirp protruding from the upper
engine bay (brake booster area) The noise sounds identical
to what a bird would make on any given day.

"Chirp chirp chirp", then slowly subsides if I bring RPM's
up or push the pedal repeatedly.

Also.. when on a cold start up, I wont have brakes AT
ALL and my E-brake light illuminates and instantly restores
pedal pressure. (very concerned, daily driven car..)

Fluid recently changed, all lines intact.. Suspicious
about a small leak, but that shouldnt hinder the brake
system like it does.

 

How much manifold vacuum at idle? If the E-brake warning light comes on you have a brake problem unrelated to engine vacuum as this light is hooked to sensor that senses an imbalance of line pressure between the front and back brakes such as if a brake line blows out or the E brake is applyed or the brake master cylinder is faulty or low on fluid.
It does not sense or warn of low brake booster vacuum. Disconnect the vacuum hose from the booster with the engine running and see that the light does not come on.
Any noise coming from the brake booster indicates a faulty booster.

 

how much duration we talking about.. at 248* @ .050 my brakes wouldnt work when the motor was cold and were a bit on the weak side, motor hot..

 

Its not a dual pattern, 282/282 .465 @ 0.50

Im not sure what the vaccum load is, Im just making
a guess. Id assume something else could be the culprit
but the lack of vacuum could be exaggerating the problem.

I had replaced a fractured driver side brake line with
a newly run line. I suspect the flare is smaller then inside
the booster and not mating, causing a blow-out.

But it is not dumping any mass amounts of fluid.

Im just glad that Emergency brake light triggers
something and restores the pedal, or I woulda had
a bigger traffic ticket then what I originally had!

 

so i'm guessing around 236* @.050.. should be working pretty good.. booster failing maybe?

 

If that's the case, Ill have to run a few more tests to
confirm. One, Replacing that brake line.. As that was the
last thing I touched on the brakes.

Ill get a guage and find out where my manifold
vacuum is lurking at..

For a Firebird at 150,000 miles to have a brake
booster fail is strange.. and I hope its not the case.

 

the E-brake light does not "restore the petal". Pumping the brakes will, temperairly. you have a hydraulic problem. has nothing to do with the vacuum.
A modified engine with a large long duration cam will idle a lot lot nicer and give a better vacuum signal if you run as much initial timing as possible.
If the manifold vacuum is as low as say 5" or lower at idle in gear @ say 900rpm, give it about 30 to 35deg BTDC at idle.

 

Well it's fixed, I think.

Pedal restored, has plenty of stop now, it was the
brake line with a smaller diameter flare for some reason.

Though it didn't leak, air was getting in there, disrupting
the hydraulic system.

The "chirp" I mentioned, did not go away though, and I
suspect the booster is on its last legs, or I did not bleed
the brakes long enough.. Ill see what happens

I'm satisfied that I am no longer a danger to myself
and others knowing I had a 300hp Fbody with no brakes

Any idea what that "chirp" could be? possible seals in the
booster going out? The car did sit for a year or so..

Thanks for the quick responses!