98 blazer brake issue

[nicchevy]

I have replaced the front and back pads, I have tried to bleed the system and still nothing, I was told that I didn't have to bleed the system after it was already done. Still had problem with spoongy brakes, replaced the master cylinder and still have issue. I'm getting fluid to the calipers but the back ones have low pressure. Could I have messed up something else in the system, like the sequencing valve next to the master cylinder? Hope someone has seen this or has an idea what to do next

[old_master]

If the vehicle has ABS there is a specific bleed sequence, (procedure) that must be followed. When replacing brake pads and/or rotors it is not necessary to open the hydraulic system, therefore it's not necessary to bleed it. The procedure can be found in Haynes and Chilton repair manuals, and possibly in this forum if you run a search.

[rlith]

Do you have a disc or drum rear?

[nicchevy]

I have disc on both front and back. I have picked up a Haynes and bleed the system according to there instruction. After bleeding the system and running the engine the pedal still goes to the floor. Do I have to bleed the EHCU and valves attached to it seprate or bleed the whole system again? If there are codes can I reset them without a scan tool? I'm at a loss of what to do next.

[old_master]

When the master cylinder was replaced, was it bench bled thoroughly before installation? If not, air will be introduced into the hydraulic system the first time the brake pedal is depressed. If the red "Brake" indicator light is on, the centering or "proportioning" valve is not centered. More than likely this is due to air being in the hydraulic system. Unfortunately this valve does not differentiate between front and rear systems. It only indicates that there is an inability to hold and retain sufficient hydraulic pressure in at least one of them. The entire system needs to be checked for leaks and then bled, using the proper procedure, in order to turn off the “Brake” light. This can be quite frustrating and time consuming, especially if you don’t know which system has air trapped in it. If the system has ABS, there are obviously more places where air can be trapped, increasing the frustration level and the time factor involved.

If there are DTC's (diagnostic trouble codes) a special scan tool designed for ABS must be used to retrieve them and reset the computer.

[nicchevy]

The master cylinder was bench bleed, then bleed the whole system according to the Hanyes manual that I have. I get a stiff pedal without the engine running, but the brake pedal goes to the floor with the engine running. Do I still have air in the system and should bleed the system again? Do I need a scanner to get the abs to run or do I need to have the system pressureized by a dealership? I'm at a loss.

[old_master]

Is the "ABS" light on? If so, you need a scan tool designed for ABS to retrieve the codes. A standard OBDII scanner will not retrieve ABS codes. From your symptoms, it sounds like the entire system needs to be bled including the EHCU.

The ABS self diagnostics require the vehicle to be running and driven approximately 20 feet to test the output of the wheel speed sensors.

[GirlBear]

When I had a hard pedal. i could push it to the floor but again it was extremely hard and it would make a shooooosh sound. the problem turned out 2b Powerbrake Booster.

[nicchevy]

Well I have given up and I'm going to get it towed to a dealer to get the brake system pressure bleed. I thinkt that is going to be the only way to get the air out of the system. So thanks for all the input.

[rlith]

Originally Posted by nicchevy

Well I have given up and I'm going to get it towed to a dealer to get the brake system pressure bleed. I thinkt that is going to be the only way to get the air out of the system. So thanks for all the input.

Another issue that hasn't been touched upon that can cause your systems is a bad brake booster.

[maxwedge]

I may be off base here, but even with a good brake system sitting still you can get the pedal almost to the floor, on these trucks. Is the brake lite on? Have you driven it and how far does the pedal go down before responding?

[joeuser742]

Originally Posted by GirlBear

When I had a hard pedal. i could push it to the floor but again it was extremely hard and it would make a shooooosh sound. the problem turned out 2b Powerbrake Booster.

After you put the new brake booster on, does it still make that shooooosh sound? I'm having brake problems and thought that it was pad/rotors glazing, but not sure now. I also have that shoooosh sound.
I hope that I'm not hijacking a thread. Thinking that it's related and no need for a new one.