Too much brake pedal pressure?

[DRGrocho]

Usually this isn't a problem, but the other day it almost caused an accident, so I figure I should look into it. I tried to search, but I'm not really sure what I should be searching for.

 

When I go on long trips in the Lumina, it seems like the pedal will pressurize. When you touch the brake, the car will start to slow, but that could be the brakes just barely engaging or just the TC unlocking. After that tho, you have to about stand on the pedal to sort of "break through" this pressure barrier and then after that it stops like normal, aside from the fact that once the pedal goes back to normal, you're still kinda standing on it so it results in some jerkiness. My fiance was driving when we almost got in an accident, so I threw it in neutral right away then she went on the rumble strips to avoid another car. She says that as soon as I put it in neutral, the brake went back to normal, but since she hadn't experience the issue before, I'm not sure whether or not she broke through the pressure or putting it in neutral actually helped.

 

My first guess is that there is a high water concentration and the "pressure barrier" is because the water is boiling or high temp and expanded, but I don't think you could just break through that

[slick]

I would definately try to bleed the brakes. Be sure to let a bit of fluid drain out, so you can put more new, fresh fluid into the system.

[Schurkey]

you have to about stand on the pedal to sort of "break through" this pressure barrier and then after that it stops like normal, aside from the fact that once the pedal goes back to normal, you're still kinda standing on it so it results in some jerkiness.

First Guess: Defective brake booster. Second Guess: two drops of moisture in the booster which turns to ice when the weather is cold and the engine hasn't been run for awhile; you have to crack the ice to get the booster to work properly. If the booster has moisture in it, you MIGHT be able to fix it by pouring in some "Heet" (alcohol) into the vacuum hole once you remove the vacuum hose and check valve; then re-install the check valve and hose, run the engine at fast idle and pump the brake pedal to move fresh air through it to evaporate the water/alcohol mix. No promises; I've never done that. Since your alternative is to replace the booster; I figure you might as well try the alcohol first...

 

My first guess is that there is a high water concentration and the "pressure barrier" is because the water is boiling or high temp and expanded, but I don't think you could just break through that

I wouldn't expect water mixed with the brake fluid would do that. Flushing the brake fluid is a good idea just as a general maintenance idea; ideally you'd do it every couple of years. So, sure, change the brake fluid 'cause it can't hurt. Still, I'd expect the problem to be in the booster.

 

I did a booster-change write-up (with photos) in this thread:

 

http://www.w-body.com/forum/index.php?topic=63764.0

[spiderw31]

My guess would be a dying booster, or not enough vacuum getting to it somehow. When the engine RPMs are lower it generates more vacuum than at higher RPMs.

 

When you mention the incident about throwing the car in neutral, that tells me that there was not enough vacuum in the booster when the brakes were hit, and the RPMs were higher because of the highway speeds. As soon as you threw it into neutral however, the vacuum would climb sharply, and the booster would do its job.

 

Hopefully this helps!

[DRGrocho]

My guess would be a dying booster, or not enough vacuum getting to it somehow. When the engine RPMs are lower it generates more vacuum than at higher RPMs.

 

When you mention the incident about throwing the car in neutral, that tells me that there was not enough vacuum in the booster when the brakes were hit, and the RPMs were higher because of the highway speeds. As soon as you threw it into neutral however, the vacuum would climb sharply, and the booster would do its job.

 

Hopefully this helps!

 

Yeah, that sounds about right because as I said it only does after I've been driving for a while on the highway, never right at startup or in city driving. I'll start with some of the things on the booster and go from there.

[toms92gpse]

I agree with it being the booster. When my went bad I had to stand on the pedal to stop, At first it would work fine sometimed and some times not but eventually it quit all together.