SweetZRag

All of a sudden, the brakes barely stop the car. The pedal goes to the floor with only medium pressure. Definitely not firm. Fluid level is fine and no signs of leaking anywhere. Pads are fine. No recent brake work and this just started happening so I don't believe it is air in the line.

I have not tried bleeding it yet. No brake light on the dash, even when pushed all the way to the floor.

Does this sound like an internal master cylinder problem to you? Maybe the the fluid is bypassing the piston?

NEWBIE T/A

Although the no brake light is puzzling.

Hopefully someone here will know more, but if the anti lock control went bad, I wonder if it could cause similar issues ? That would explain the no bulb - although a burned out bulb could also cause that, too.


Sad to say, but due to the location of the brake booster & master cylinder and the potential bleeding issues w/ anitlock brakes I would probably have a shop look at it.


Good Luck !


Britt

SweetZRag

I don't think it is a problem with air in the system because I have no leaks and have not done any brake work for a while so the system has not been opened. It just started happening. I'll do a bulb check to see if the bulb works. Just in case, I plan to bleed them tonight.

It just feels like the MC is not generating any pressure, maybe the fluid is bypassing the seals on the internal piston.

The MC is about $80 - 90 so I want to be sure before I spend the money.

n2ceptor

My guess, the master cylinder is bypassing....... Bleed the brakes first, just to make sure...

SweetZRag

Thanks. I am going to do this tonight.

ZDriver96

A brake booster not flush against your firewall can cause loss in brake pressure. A faulty brake booster can also cause what your describing.

SweetZRag

If the booster was defective, wouldn't the pedal be harder to push? In my case, it goes to the floor with out much pressure. Not like there is a brake in the line, just easier than it should. The booster is tight to the firewall.

How can you accurately test the booster? Would a vacuum pump work to see if it holds vacuum?

ZDriver96

excuse me. I meant the master cylinder flush against the brake booster.

With the engine off pump your pedal until it is firm.. Normally takes 3 or so pumps... Once its firm hold it and if the pedal becomes soft and you are able to push it to the floor then the seals in your master are bad...

Now if it holds just fine while the engine is off then its likely your brake booster because while the engine is running your using the vacuum off your booster to get your brake pressure right off the bat instead of a few pumps like when the engine is off.

SweetZRag

That makes sense. Thanks. I have 390,000 miles on this master cylinder. Gonna test and/or replace it tonight.

SweetZRag

Update - I have replaced the master cylinder and all the rotors and pads have less than 9,000 miles on them. All check out fine. No fluid leaks and I have bled all lines and successfully bench bled the MC.

When the engine is off, the pedal is firm and grabs high like it should. When I start the engine, the pedal goes to the floor under normal pressure and the brakes barely stop the car.

Does anybody have an idea what is going on with this? I am stumped.

ZDriver96

brake booster

SweetZRag

Per the GM manual, if the booster was bad, the pedal would be harder to push than normal. It definitely gets much easier to push when the engine is running. The pedal is high and firm when not running but goes to the floor when running. It seems the booster is working.

What I don't understand is if the booster just assists, why does the pedal go to the floor when the engine is running. I bled the brakes twice purging all the old fluid both times. I don't get any air out of it.

In the manual that came with the MC, it says if the MC is mounted on an angle, to jack the rear of the car up until it is level as air might get trapped in the system. Has anyone found this necessary on the Camaro? I jacked it up some but not high enough to level the MC.

ZDriver96

Typically your pedal will get hard but it can get soft. Like if your MC is not flush against your booster.

I'd take the booster off and check for cracks/opening
If you have a vacuum gauge you can checks for leaks.
Your idle might be slightly erratic.. going up and going down in rpms.
Sometimes you'll here a hissing or swooshing sound from the booster when pressing the pedal.

when you bleed your system start with the farthest point away from the MC. The MC is not at an angle on our cars. You can try raising the back higher than the front when bleeding the rear.

There's not much else in the braking system... Your MC, your lines, booster..

SweetZRag

I appreciate the tips. Some clarification: I have bench bled the MC twice and it is tight to the booster. Idle is good and I have a vacuum guage so I'll check to be sure. On my 94 the MC is mounted at an upward angle. I bled all 4 wheels twice starting at the farthest wheel. I get good flow out the bleeders so I know there are no clogged lines. No air bubbles either.

Would a vacuum pump on the booster prove that it works if it holds vacuum? I don't think it is the booster so I want to prove it before spending the money on it. I already bought a new MC and new rear rotors because they were a little thin.

Thanks again and let me know if anything else comes to mind....

ZDriver96

I think this is how it works....
Because if the MC is not flush against the Booster Excess air comes in and the pedal gets soft.. There is an opening in the middle of the booster where is connects to the MC.
If your valve on the tip of your hose that connects to the brake booster is broke/shut your brakes get hard as hell to push in. You can blow through the hose to see if its flowing but i'm sure it is otherwise your pedal would be hard.

You have a diaphragm inside the booster.. not sure how to diagnose that part...