Brake Problems

[Metallica9156]

Recently my 1998 Chevy Blazer LS 4x4 has had some issue concerning the brakes. I have had a problem with a lack of pressure in my brake pedal. I have to press my brake pedal all the way to the floor for it to stop, and even when I do that its still has a hard time stopping. I bled the brake lines by using the gravitational method and replaced the front brake pads (the rears had about 80% of pad left). This still did not fix the problem, so I bled the brake lines again to find that somehow air got back into them. Does anyone have any advice on what to do next?

[DINO55]

Do you hear any hissing sounds when you push the pedal to the floor?
Did you recently do a brake job on it and got air in the lines?

If you answered no to the questions above, then you more then likely have a bad master cylinder on your hands.

[Metallica9156]

Yes I hear a hissing sound when a press down the pedal, and the problem was there before I changed and bled the brakes.

[DINO55]

Hissing sound while pushing pedal down to the floor = Bad Brake Booster

[joeuser742]

I had a problem with the rotors and pads glazing, I had to push real hard to get it to stop and they still wouldn't lockup. The brakes were no more than a year old. Turned out that I changed all the pads and rotors and found 2 locked up slider pins right rear. That was most likely causing the brakes to glaze.

[Corey96LS]

my truck is doing the same thing, and if you hit the brakes suddenly and hold them down, it starts to make a whining noise until you come to a stop.. but it only does this if you come to a sudden stop.. could this be the brake booster being badd.?

[rpeery]

98 Chevy- Brakes-
I am experiencing brake problems. While I am driving at low speed and gently apply the brakes, the truck continues to move ahead and the brake peddle has a jittering, pulsing affect, in which does not seem to stop the vehicle unless I push really hard and allow room between me and the other vehicle. Any suggestions?

[muddog321]

See if the large vac line from the intake to the booster is firmly connected on both ends - intake end can rotate and unlock off the intake connector and the booster has a large rubber gasket on it. Then with the Blazer running dothe brakes work - pedal will drop on these - the ABS will engage on sensor seeing speed mismatches and cause a definate noise as it works but if the feel is always pulsing on every stop then probably rotors need to be turned. But if the ABS fires on most stops and the ABS light is on read the codes out now.

Did you replace those rear calipers - often they are a problem cause the piston binds and they get hot and the fluid gums up in the caliper. If your hoses are expanding they too can be a cause. I've had to remove the bleeders on an 01 cause they were rusted and would not correctly flow so bleeding was not working - if the flow out the bleeder is really slow and low with it opened a full turn they are bad.

[tj888]

I have been having brake problems on my 99 Blazer LT - the pedal feels spongy, has excessive travel and the anti-lock sometimes comes on when braking even though it shouldn't. When this happens, the pedal seems to go down even further. The antilock light is not on, but the brake light does occasionally come on. There is no fluid loss, I have inspected front and rear disks, pads, calipers, lines and everything seems to be in order. The master was replaced and I have bled the system a few times - it seems to improve a little bit, but only temporarily.

Does anyone have any suggestions on what could be causing this? I have heard that is posisble to get air trapped in the anti lock unit and that this requires special tools and a special bleeding procedure. Is anyone familiar with this?

[DINO55]

THIS WAS COPIED FROM AF MEMBER SOUTHERN COMFORT

BLEEDING BRAKE SYSTEM
ABS BLEEDING PROCEDURE

NOTE: Bleeding ABS system requires the use of Tech 2 scan tool. An
assistant is required when performing bleeding procedures.
1) Raise and support vehicle. Begin bleeding at right rear
wheel. Install a clear plastic hose to bleed screw. Immerse other end
of hose in container that is partially filled with clean brake fluid.
2) Open bleed screw 1/2 to 1 full turn. Have assistant slowly
depress brake pedal until it reaches full travel. Hold pedal until
bleed screw is closed. Release brake pedal and wait 10-15 seconds.
Repeat until clean bubble-free brake fluid is present at wheel bleed
screw.
3) Check master cylinder fluid level every 4-6 strokes of
brake pedal to avoid running system dry. Repeat steps 2) and 3) on
left rear, then right front, then left front. After bleeding all 4
wheels, go to next step.
4) Using scan tool in FUNCTION TEST, run FUNCTION TEST 4
times consecutively while applying the brake pedal firmly. Release
brake pedal between each test.
5) Rebleed all 4 wheels to remove remaining air from brake
system. Ensure brake pedal feel is appropriate before attempting to
drive vehicle. Rebleed as many times as necessary to obtain
appropriate pedal feel.
I have always done the cars I work on that way and never had any problems with the ABS. I compressed them slowly and all the cars and trucks I have worked on , still have the ABS system working fine.
Just thought I mention that. I hope what I posted up above helps you.

[tj888]

Thanks for the info. Sorry for the delayed response, but I was offline for a while.

I think I know somebody with the right tool so I will try this out. When running the TEST with the brake pedal depressed firmly, are all the bleeder screws closed? I assume the test will cause the antilock unit to pulsate so any trapped air can escape the unit into the lines, but how does the air bleed out if the system is closed (i.e. all bleeders are closed)?