brake problem, VERY hard brake pedal but VERY little braking power

[95GMCJimmySLE]

I just replaced the brake pads a couple weeks ago but don't this has anything to do with it, but just in case I figured I should mention it.

Today, about a couple hours ago, the brake pedal started to get very hard to push and wasn't stopping the car very well. Eventually it got to the point that I had to put the car into neutral when coming to a light and literally stand with both feet on the brakes to get the car to stop. Sitting at the light I had to keep it in neutral because if I wasn't standing on the brake pedal and only holding it with one foot with moderate pressure the car would still move if in gear. I babied it home and here I am.

I looked at the brake MC reservoir and it has plenty of fluid. Nothings appears to be leaking from the calipers. One thing I did find weird was that while pushing on the brake pedal with any amount of pressure you can hear what I would describe as a hissing sound coming from above the brake pedal area like where the push rod (or whatever it's referred to as) goes through the firewall and to the brake booster and brake MC. I don't recall it ever sounding like this so is this an indication of what the problem is?

Could it be air in the lines? I don't see why since I haven't had the lines open at all.

Or could it be the brake booster? Not sure of the symptoms that this would cause.

I looked at the vacuum line that goes between the brake booster and the back of the IM and it looks fine so...

I would say the best way to describe how it feels is like trying to stop the car when it stalls, like there is nothing there to help power the brakes.

any help is greatly appreciated. This is my girls car and I've been driving it while I finish a few things on my car, so I need to have this fixed by the end of tomorrow to drive it to work on Monday.

Thanks

[TomB985]

Well, if the pedal is firm and does not feel spongy or go to the floor, it is NOT a fluid leak. Sounds like a vacuum leak or a bad brake booster. How does it run? Any problems at idle?

[95GMCJimmySLE]

the idle seems fine.

The idle does seem to idle up a little when I'm standing on the brake pedal.

A couple times while pressing the pedal repeatedly and then holding it idle went up a little and then after letting go the idle seemed to drop a little below normal but came right back up with no other fluctuation.

[tempfixit]

Originally Posted by 95GMCJimmySLE

the idle seems fine.

The idle does seem to idle up a little when I'm standing on the brake pedal.

A couple times while pressing the pedal repeatedly and then holding it idle went up a little and then after letting go the idle seemed to drop a little below normal but came right back up with no other fluctuation.

I agree with TomB985 that is likely a booster proble. Check this site out: http://www.autozone.com/az/cds/en_us...es.htm#hd1-1-3 it describes how to check the booster for proper performance.

Hope this helps

[95GMCJimmySLE]

thats sorta what I was thinking but thats why I wanted to ask.

I keep getting a "server unavailable" message when I click on that link.

[tempfixit]

Originally Posted by 95GMCJimmySLE

thats sorta what I was thinking but thats why I wanted to ask.

I keep getting a "server unavailable" message when I click on that link.

Go to Autozone.com. Then to repair info and then year and make then it will show a list, click on brakes, then power booster and it will give you the procedure.

[95GMCJimmySLE]

it just wont let me on the site for some reason. Which is weird cause I was just on there a little bit ago looking at the replacement procedure for the booster. I didn't see the testing procedure though.

[tempfixit]

Originally Posted by 95GMCJimmySLE

it just wont let me on the site for some reason. Which is weird cause I was just on there a little bit ago looking at the replacement procedure for the booster. I didn't see the testing procedure though.

Vacuum Leak Test

1. Operate the engine at idle without touching the brake pedal for at least one minute.
2. Turn off the engine and wait one minute.
3. Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.

System Operation Test

1. With the engine OFF, pump the brake pedal until the supply vacuum is entirely gone.
2. Put light, steady pressure on the brake pedal.
3. Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained.

Power brake systems may be tested for hydraulic leaks just as ordinary systems are tested.

Hope this helps

[95GMCJimmySLE]

Originally Posted by tempfixit

[*]Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.

so if the pedal moves les and less with light pressure being applied over and over then there is vacuum in the booster and everything is working right? But if the pedal doesn't move less and less then I'm leaking vacuum and the booster is bad?

Originally Posted by tempfixit

[*]With the engine OFF, pump the brake pedal until the supply vacuum is entirely gone.

How do I know when vacuum is entirely gone?

[tempfixit]

Originally Posted by 95GMCJimmySLE

so if the pedal moves les and less with light pressure being applied over and over then there is vacuum in the booster and everything is working right? But if the pedal doesn't move less and less then I'm leaking vacuum and the booster is bad?



How do I know when vacuum is entirely gone?

That is the way I interpet it also.

POWER BOOSTERS
Virtually all modern vehicles use a vacuum assisted power brake system to multiply the braking force and reduce pedal effort. Since vacuum is always available when the engine is operating, the system is simple and efficient. A vacuum diaphragm is located on the front of the master cylinder and assists the driver in applying the brakes, reducing both the effort and travel he must put into moving the brake pedal.
The vacuum diaphragm housing is normally connected to the intake manifold by a vacuum hose. A check valve is placed at the point where the hose enters the diaphragm housing, so that during periods of low manifold vacuums brakes assist will not be lost.
Depressing the brake pedal closes off the vacuum source and allows atmospheric pressure to enter on one side of the diaphragm. This causes the master cylinder pistons to move and apply the brakes. When the brake pedal is released, vacuum is applied to both sides of the diaphragm and springs return the diaphragm and master cylinder pistons to the released position.
If the vacuum supply fails, the brake pedal rod will contact the end of the master cylinder actuator rod and the system will apply the brakes without any power assistance. The driver will notice that much higher pedal effort is needed to stop the car and that the pedal feels harder than usual.

I am not sure how you can tell when the vaccum is entirely gone.

Look at the check valve at booster it could possibly be faulty. I would think it should rattle when off the booster. I will expirement on my 96 Silverado in the morning and post back with info.

[95GMCJimmySLE]

ok, well I just went out and tried both of those tests.

the System Operation Test:
I pumped the brake pedal and then held it in and started the engine. The pedal didn't move and I could hear that same hissing sound from the pedal area. I could hear it from when I started the engine until I removed my foot from the brake pedal to do the next test.

the Vacuum Leak Test:
I let the engine idle for a minute without touching the brake. Then I turned it off and let it sit for another minute without touching the brake. Then I started pressing the brake pedal and the amount the pedal moved didn't seem change at all.

What does all this mean?

[95GMCJimmySLE]

Originally Posted by tempfixit

Look at the check valve at booster it could possibly be faulty. I would think it should rattle when off the booster. I will expirement on my 96 Silverado in the morning and post back with info.

That would be great!

That was my next question. How am I to know if it's the vacuum hose/check valve problem or a brake booster problem?

I would hate to buy and replace the booster just to have it end up being the check valve or vacuum hose.

[tempfixit]

Originally Posted by 95GMCJimmySLE

ok, well I just went out and tried both of those tests.

the System Operation Test:
I pumped the brake pedal and then held it in and started the engine. The pedal didn't move and I could hear that same hissing sound from the pedal area. I could hear it from when I started the engine until I removed my foot from the brake pedal to do the next test.

the Vacuum Leak Test:
I let the engine idle for a minute without touching the brake. Then I turned it off and let it sit for another minute without touching the brake. Then I started pressing the brake pedal and the amount the pedal moved didn't seem change at all.

What does all this mean?

The booster is leaking internally or the line going from intake to booster is leaking. Take a small (1/4") hose and listen to the hose from the intake to booster if it is leaking you should be able to hear it. If that doesn't leak I would say your booster is bad. Hopefully some one else will chime in to confirm my thoughts. Let us know what your fix happens to be.
Good Luck

[95GMCJimmySLE]

Originally Posted by tempfixit

Take a small (1/4") hose and listen to the hose from the intake to booster if it is leaking you should be able to hear it.

umm... I'm confused as to how I should use a small hose to listen to the booster hose for a leak. I have some hose that I was using on my car so thats not a problem, I just want to make sure I understand how you are saying to check it.

[tempfixit]

Originally Posted by 95GMCJimmySLE

umm... I'm confused as to how I should use a small hose to listen to the booster hose for a leak. I have some hose that I was using on my car so thats not a problem, I just want to make sure I understand how you are saying to check it.

Using a hose will help you hear where the leak is or take a can of carb cleaner or brake cleaner and spray the hose to booster if it is leaking you will hear a difference in the egine idle.