Jorday

This issue has appeared the last few days. I notice that when the car sits for a couple of hours or more there is no vacuum boost on the brake pedal when I get in and put my foot on the brake until I start the engine. I replaced the check valve and rubber grommet where the vacuum line connects to the booster with no change. What else can I check? Is the booster itself bad? I just don't want it to become a problem while I'm driving if the leak gets bad enough.

glenB

And your indications of this are?

JKbride

Well sounds like that could be the problem. I would do a complete vacuum check on the car first. Sounds like you are checking the right things....could be a leak from another source?

The booster has a diaphragm that may have gone bad, but that usually happens on much older cars. Are you getting an ABS light?

If its not a vacuum problem, then next will be to replace the booster.

Jorday

I don't know how else to explain it other than to say that when you shut the car off the brake booster loses its vacuum and there is no assist on the brake pedal.

Jorday

Yeah, I think the next step is going to be to just replace the booster. Really, there are only 3 ways this could be happening. It's either the the check valve, the rubber grommet or the booster itself is leaking. I replaced the check valve and grommet already which didn't help, so that sort leaves one possibility the way I see it.

No ABS light, brake lights or anything like that. Car drives perfectly. I've just noticed that after a few hours the car doesn't have any vacuum assist when you get in and press the clutch and brake pedal to start it up.

haljensen

What is happening that leads you to believe that the booster is "losing" vacuum?

How long do you expect the booster to hold vacuum? What about cars that are stored for months?

glenB

Personally I think you're chasing ghosts, boosters rarely fail, but, in fairness, start the car and allow vacuum to build in the booster, shut off the car and wait about 5/10 mins, then remove the valve from the booster and listen for a hissing sound, the air rushing in, as you remove the valve, no hiss... you have a leak, hiss'..... no leak.

A booster w/o vacuum is only going to give about half the normal pedal drop once it loses it's constant source, one time. After that it will be pretty firm.

Mine can sit all day and the pedal will be hard, yet it will still have vacuum in the booster.

Jorday

It always has vacuum after sitting overnight and then suddenly it doesnt seem to in the morning anymore. That's why I started looking into it.
You might be right that It's nothing to worry about. I just didn't want to ignore this if it was maybe a sign that the booster might go out during driving at some point. Sounds like it's probably nothing.

bolivar

Ok, my story about a booster leak. This was on a 1993 Pontiac van, so not very close to a newer Corvette. And it was my father-in-laws.

But, pressing on the brake while in park changed the idle. I think it increased the idle. The car still had brakes, but they were getting harder and the idle was changing, and I think when you shut it down you could hear the hiss of a leak.

I wasn't able to fix the thing myself because with the short nosed van, there was not room to get the booster out of the car. There didn't look to be room to drop in down either, so I had him take it to an alignment and brake shop. They got it out, did not ask how.

haljensen

You say "it suddenly doesn't seem to in the morning anymore".

What doesn't seem to? What is different now? No pedal? High pedal? Sinking pedal?

BTW; I used to live in Fenton. Is the Kmart there still open?

Jorday

This is what has changed:

PREVIOUSLY:

EVERY day I go to drive the car to work. I get in. I depress clutch pedal and also brake pedal so car doesn't roll. When I press on the brake there is always some vacuum assist at that time even though the engine hasn't started yet.


NOW:

I get in. I depress clutch pedal and brake pedal. Brake pedal is now hard to depress until engine starts.

There is no change in the car's behavior once it's running. The loss of vacuum assist on the pedal prior to engine startup is the only thing that's changed.



Yup, I believe the kmart is still here.

JCtx

You'll always lose vacuum given enough time (similar thing with fuel rail pressure). The better question is 'how long' that time should be. Since I have a manual (just like you), and I always use the parking brake, I have never push the brake pedal before starting the car, to give you an idea how quickly the pedal hardens on my car, but maybe those with automatic trannies (same braking system) can chime in. I can tell you on my automatic cars, brake pedal is always hard after sitting overnight, so I wouldn't worry about it just yet. But the fact you're noticing a difference means something is wearing out. How old is your car and how many miles? You should always start with that information .

Jorday

It's an 09 with 16k miles.

KB9GKC

Hello,

Your car is working fine, enjoy it and get out in the sunshine.

Douglas in Green Bay

Jorday

Just to revisit this one briefly, my buddy has a 2012 and it does NOT do what my car is doing. Im not sure it means anything since the car still drives perfectly fine. I'll just keep an eye on it for now, I guess.

bob guzzy

Why not just change the booster check valve, it just pulls out and the new one pushes right back in, the whole operation should take you no more than a few minutes.

I doubt on a new car like yours the booster has gone bad, but the check valve is just a small plastic piece with a rubber valve inside that I could believe might be defective.

AtomicZ_Eric

EDIT: Posted in the wrong tab. Please ignore.