Brakes gone wild!

[daves-a-killer]

I have a 1996 GMC Jimmy, 2WD 4-Dr. The problem I am having is when I step on the brakes, it's almost like the front are failing, the rear are locking, and Im not stopping correctly. Last week the only reason I didnt rear end someone is because there was no one in front of me.
It's almost like I am trying to stop on ice...even though it's 60 degrees. Anyone have any idea what I can do?

I have read a few things, and I am at a loss. I was tryin to read how to disable the ABS system to try to narrow it down, but the girls in that thread (How to disconnect ABS) just argued instead of getting anything accomplished!
Is there a fuse I can dissconnect just to test if it is the ABS system?

Please any help would be appreciated!!!

[MT-2500]

Originally Posted by daves-a-killer

I have a 1996 GMC Jimmy, 2WD 4-Dr. The problem I am having is when I step on the brakes, it's almost like the front are failing, the rear are locking, and Im not stopping correctly. Last week the only reason I didnt rear end someone is because there was no one in front of me.
It's almost like I am trying to stop on ice...even though it's 60 degrees. Anyone have any idea what I can do?

I have read a few things, and I am at a loss. I was tryin to read how to disable the ABS system to try to narrow it down, but the girls in that thread (How to disconnect ABS) just argued instead of getting anything accomplished!
Is there a fuse I can dissconnect just to test if it is the ABS system?

Please any help would be appreciated!!!

Is the ABS light coming on?
Is the brake pedal kicking up and down?
Is brake pedal going to the floor.
What is the service history on brakes?
Any brake fluid loose?
We can not advise you on how to disable ABS brakes.
Only how to fix them.
It is a safety issue.

[daves-a-killer]

Well, what I have read so far is the ABS system in this particular vehicle is retarded.

Anyways, with that said, to answer your questions:

1. The ABS light is not coming on.
2. The brake pedal is not "kicking up and down".
3. When I am stopping the vehicle, the pedal goes practically to the floor.
4. I just replaced the pads and shoes in the truck about 3 weeks ago. The rear wheel cylinders were replaced. The front calipers were replaced. The rear return springs were replaced. The front bearings were replaced. And the front rotors are brand new.
5. And I havent noticed any brake fluid loss.

Im not trying to permanently disable the ABS. I just want to narrow down where the problem might be.

[MT-2500]

Originally Posted by daves-a-killer

Well, what I have read so far is the ABS system in this particular vehicle is retarded.

Anyways, with that said, to answer your questions:

1. The ABS light is not coming on.
2. The brake pedal is not "kicking up and down".
3. When I am stopping the vehicle, the pedal goes practically to the floor.
4. I just replaced the pads and shoes in the truck about 3 weeks ago. The rear wheel cylinders were replaced. The front calipers were replaced. The rear return springs were replaced. The front bearings were replaced. And the front rotors are brand new.
5. And I havent noticed any brake fluid loss.

Im not trying to permanently disable the ABS. I just want to narrow down where the problem might be.

You are on your own on disabling the abs brakes.
But with no abs light and no pedal pulsating it sounds like you problem is with the regular brake part.
Is the rear adjusted up good?
Is the master cylinder bleeding off or creeping down?
If calipers and cylinders have been replaced you may have air in the system.
If it is a 4.3 engine?
To bleed or check the ABS system BPMV you will need a gm tech 1 scanner with a ABS cartridge or a high end scanner capable of testing and bleeding ABS brakes.

I would give the system a good bleeding and check the rear brake adjustment.
Let us know how it goes

[daves-a-killer]

It is a 4.3 engine.

[daves-a-killer]

When I push the brake pedal down, there is a hissing sound right at the pedal area. Could this be a result of a failing brake booster? Could a failing brake booster be my problem, would a failing brake booster have the symtoms I desribed earlier?

[MT-2500]

Originally Posted by daves-a-killer

When I push the brake pedal down, there is a hissing sound right at the pedal area. Could this be a result of a failing brake booster? Could a failing brake booster be my problem, would a failing brake booster have the symtoms I desribed earlier?

No
A bad booster or ABS unit will not cause a low pedal.
In fact it goes the other way around on the vacuum booster.
No vacuum or a bad vacuum booster will cause a full pedal.
Can you hear a vacuum leak when you hold the pedal down?
Shut off the engine and pump the brakes a few times and see if you have a full pedal.
If not you have a bad master cylinder or air in system or the rear brakes are not adjusted up good.
Any brake fluid loose?
Have you adjusted up the rear brakes?
Have you bleed the brakes with a ABS capable scanner?

[daves-a-killer]

When the truck is off:
I have full pedal and no hissing sound.
When the truck is running:
Pedal goes to the floor and there is a hissing/whooshing sound. Is that what a "vacuum leak sounds like?
I havent noticed any loose brake fluid. (I assume that's a leak?).
I havent bled the brakes with a ABS capable scanner. Im afraid to drive it anywhere with the brakes acting like they are.
As for adjusting the rear brakes, I havent done that. I will post-lunch!

Thanks for the help!

[Scrapper]

i would also say you still have air in system like the guy sais or your master cylender going out because it can use fluid and sometimes not use fluid when cylender going out...good luck...

[MT-2500]

Originally Posted by daves-a-killer

When the truck is off:
I have full pedal and no hissing sound.
When the truck is running:
Pedal goes to the floor and there is a hissing/whooshing sound. Is that what a "vacuum leak sounds like?
I havent noticed any loose brake fluid. (I assume that's a leak?).
I havent bled the brakes with a ABS capable scanner. Im afraid to drive it anywhere with the brakes acting like they are.
As for adjusting the rear brakes, I havent done that. I will post-lunch!

Thanks for the help!

I can not say for sure but it sounds like a bad booster.
A full pedal and no seep down with engine off indicates the regular braking system is good.
Does the pedal bottom all of the way down or just 3/4 7/8 the way down with engine running?
If you can hear a vacuum leak/swishing/sucking sound after holding down on pedal the booster is leaking inside.
Also when pedal held down engine running is any noise/viberation felt on the ABS unit?
To bypass the ABS unit only for a test and do not drive it on the road bypassed pull the fuse or relay.

[MT-2500]

Another thing to check for.
Does all brake waring lights come on for a bulb check when key is first turned on?
ABS amber and brake red lights?

[daves-a-killer]

The brake pedal does bottom all the way with the engine running. After holding the brake pedal down, there is no leak/swishing/sucking sound. The ABS unit does move a little bit when pressing the brake pedal down. But also, something I just noticed, there appears to be bubbles (or something) coming back into the fluid resevoir. Then when I take the cover off the resevoir....the rubber piece under it looks like it's being sucked into the resevoir.

This seems weirder now. What could this be a sign of?

Also, I cant find where the ABS Fuse is.

[daves-a-killer]

1996 GMC Jimmy, 4DR, 2WD (Rear), 4.3L, V6.
I believe I have found a leak in one of my brake lines (explains my problem I think).
I think I can tell which line the leak is coming from. Where can I get a layout of which line is where? I need to go buy a new one, but Im not sure how to explain which line it is.

Thanks.

[daves-a-killer]

I believe I have found a leak in my brake lines.
Do you know where I can find a layout and description of the brake line system to purchase a brake line?

[Scrapper]

try autozone.com if they have it they will print it out 4 you...