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


95GMCJimmySLE
07-14-2007, 10:57 PM
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
07-14-2007, 11:06 PM
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
07-14-2007, 11:35 PM
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
07-14-2007, 11:55 PM
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/0900823d/80/18/ca/75/0900823d8018ca75/repairInfoPages.htm#hd1-1-3 it describes how to check the booster for proper performance.

Hope this helps

95GMCJimmySLE
07-15-2007, 12:04 AM
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
07-15-2007, 12:08 AM
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
07-15-2007, 12:14 AM
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
07-15-2007, 12:19 AM
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

Operate the engine at idle without touching the brake pedal for at least one minute.
Turn off the engine and wait one minute.
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

With the engine OFF, pump the brake pedal until the supply vacuum is entirely gone.
Put light, steady pressure on the brake pedal.
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

http://www.autozone.com/images/grey_line.gif

95GMCJimmySLE
07-15-2007, 12:26 AM
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?

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
07-15-2007, 12:56 AM
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
07-15-2007, 01:03 AM
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
07-15-2007, 01:07 AM
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
07-15-2007, 01:19 AM
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
07-15-2007, 01:24 AM
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
07-15-2007, 01:40 AM
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.

95GMCJimmySLE
07-15-2007, 07:54 AM
oh, so you mean to put one end of the hose to my ear (obviously) and hold the other end near the connection of the hose to booster connection and see if I can hear any air leaking from around that area.

I'll give both the hose and carb cleaner a try.

Thanks, I'll let you know how it goes.

tempfixit
07-15-2007, 09:50 AM
oh, so you mean to put one end of the hose to my ear (obviously) and hold the other end near the connection of the hose to booster connection and see if I can hear any air leaking from around that area.

I'll give both the hose and carb cleaner a try.

Thanks, I'll let you know how it goes.

I checked my truck this morning. First before even starting my truck I removed the vaccum line from the booster itself, I could hear the vaccum escaping the booster. Then reinstalled line to booster.
Second I pumped the brake pedal several times, kept slight pressure on pedal and started engine , the pedal dropped towards the floor meaning my system is operating properly.
Third I let it idle for couple minutes shut off and waited several minutes then pumped the pedal and the travel distance became less with each pump meaning vaccum is prresent.

Hope this helps clarify how it should work.

95GMCJimmySLE
07-15-2007, 12:40 PM
yeah, it verifies that I did in fact fail both tests. I appreciate all your help in correctly diagnosing this problem.

I just got back from AutoZone, returned the old booster for the core. Everything is working fine now after replacing the booster.

When I went there to get the new booster I asked if they sold the check valve too and she said it's included with the new booster and they don't sell them separately so... But no worries now, replacing the booster and check valve fixed the problem.

The bolts under the dash holding the booster on was probably the hardest part of the job, they are in difficult areas to access, especially if you have bigger hands. Getting the booster out was a little frustrating as well but will a little force and some gentle moving of the brake MC I was able to get enough room and get it out. Getting the new one in was much easier. Took about 1 hour to get everything apart and out but only about 30min to get the new booster in, bolted down and the MC bolted back onto the booster and probably another 30 min of get things ready to start and cleaning up after. So about 2 hours total time. Not bad IMO.

Thanks again!

tempfixit
07-15-2007, 12:47 PM
yeah, it verifies that I did in fact fail both tests. I appreciate all your help in correctly diagnosing this problem.

I just got back from AutoZone, returned the old booster for the core. Everything is working fine now after replacing the booster.

When I went there to get the new booster I asked if they sold the check valve too and she said it's included with the new booster and they don't sell them separately so... But no worries now, replacing the booster and check valve fixed the problem.

The bolts under the dash holding the booster on was probably the hardest part of the job, they are in difficult areas to access, especially if you have bigger hands. Getting the booster out was a little frustrating as well but will a little force and some gentle moving of the brake MC I was able to get enough room and get it out. Getting the new one in was much easier. Took about 1 hour to get everything apart and out but only about 30min to get the new booster in, bolted down and the MC bolted back onto the booster and probably another 30 min of get things ready to start and cleaning up after. So about 2 hours total time. Not bad IMO.

Thanks again!

Glad to be of assisstance. Thanks for posting fix

ericn1300
07-15-2007, 05:10 PM
does the problem go away after it sits for a couple of hours or overnight, then come back when driving?

StLouisJohn
10-24-2009, 02:20 PM
Boy, I wish replacing the brake booster on my 2001 Jimmy was as easy as described above. But it's not. I can't get to the top right bolt. I understand I have to lower the steering column. Right now, I've got the brake stuff all apart, 3 bolts off, but haven't attempted to lower the steering column. And the Haynes manual is of no help. Can anyone help out with some suggestions? How to lower the steering column? Or another way to get at this bolt? I would really appreciate it, I'm sorta desperate right now and would rather not pay nearly $1,000 to have it towed to a shop and have them do the work. Had I known what I would have been going through, I would have done that in the first place. Now I'm stuck. Thanks in advance for any help and advice. John 2001 GMC Jimmy

MT-2500
10-24-2009, 02:31 PM
Boy, I wish replacing the brake booster on my 2001 Jimmy was as easy as described above. But it's not. I can't get to the top right bolt. I understand I have to lower the steering column. Right now, I've got the brake stuff all apart, 3 bolts off, but haven't attempted to lower the steering column. And the Haynes manual is of no help. Can anyone help out with some suggestions? How to lower the steering column? Or another way to get at this bolt? I would really appreciate it, I'm sorta desperate right now and would rather not pay nearly $1,000 to have it towed to a shop and have them do the work. Had I known what I would have been going through, I would have done that in the first place. Now I'm stuck. Thanks in advance for any help and advice. John 2001 GMC Jimmy

This is a old post.
Always check date on a post and if old.
Best to start your own New thread.

A all data online subscription has a good detail instructions on how to do it.
http://www.alldata.com/products/diy/index.html

It says the steering column support bracket has to be removed to get to it.
But booster replacement is not a quick easy job.
Flat rate time is abiout 5.2 hrs.

Good Luck

StLouisJohn
10-24-2009, 03:05 PM
Sorry...I thought I was doing a good thing by searching before opening a new thread. :( But thank you for the info. I checked and subscribed to the Alldata site, but didn't find much on removing that column bracket. I think I'm just stuck for the weekend and will have it towed out Monday. Thanks anyway. John

MT-2500
10-24-2009, 03:41 PM
Sorry...I thought I was doing a good thing by searching before opening a new thread. :( But thank you for the info. I checked and subscribed to the Alldata site, but didn't find much on removing that column bracket. I think I'm just stuck for the weekend and will have it towed out Monday. Thanks anyway. John
Yes
Searching is a good thing.
Even check the S-10 how to section.

But if a post is old just leave it old.
If you have a problem on your truck always start your own New thread.
Saves on high jacking another post.

In All data you will find the information on steering column bracket removal under steering section and then look under bracked removal.

You have to learn how to navagated around in all data.
If you have a problem with all data they have very good support.
E mail or contact them and they will help you or even fax/send you aditional information if needed.

The insturment cluster has to come out to get to steering column bracket.
One of the reasons 5.2 hrs flat rate time on booster replace.
Good luck

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