Help with brakes before I pull my hair out
- Thread starter cofferson
- Start date
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petethepug
Michael
Brake dragging can be deteriorating brake lines. They deform and allow pressure to be retained in the lines.
They should be upgraded to braided stainless to prevent expansion as well as swapped out every decade.
They should be upgraded to braided stainless to prevent expansion as well as swapped out every decade.
Pete is spot on with this. The OEM brake lines are an issue, breaking down on the inside.
I also use the Motive pressure bleeder... Never an issue with it. And always follow up by commanding and abs bleed with an aftermarket by directional scanner.
If all that has been done, I would be looking at that master cylinder. First verify the part number is correct for your application. If so, return it as defective and pick up a genuine GM or AC Delco. (New, not rebuilt)
As you said, brakes are pretty simple. You have a defect somewhere and there's only so many somewheres that exist.
from what I read he's replaced the rubber lines and ran abs bleed with a scanner.
being a hydro boost, it seems we just had someone here post about replacing a master and the push rod length being to long. double check that. if your rod between the 2 is slightly to long and it doesn't let the piston in he master completely release. it will cause all kinds of issues.
double check that. needs a bit of a air gap when fully releasing the pedel.
being a hydro boost, it seems we just had someone here post about replacing a master and the push rod length being to long. double check that. if your rod between the 2 is slightly to long and it doesn't let the piston in he master completely release. it will cause all kinds of issues.
double check that. needs a bit of a air gap when fully releasing the pedel.
Yes ... And that's where verifying the part number to the application comes in. Very important to compare the part you're taking off with the replacement in all dimensions as well.
Definitely does sound like a master cylinder issue.
Definitely does sound like a master cylinder issue.
Haha I was the one with the gap. Unfortunately it is the right parts so idk why they didn't fit together neatly. It was ACDelco 18M2564 for the master cylinder and the booster is Bosch 0204777579. I ended up pulling out the rod on the booster and removing material until it was just .030 gapped. Kept it a nice polished rounded tip and it worked nice. A little update though, even though it's ACDelco and it would be strange if it's a bad new master, I returned it for a replacement because no matter what I do with even a pressure bleeder, air makes its way back in the master. Whether it's circling back from the ABS modulator or leaking in through seals I just don't know. Now if I bench bleed this master cylinder and STILL get air back in it once on the vehicle, I also ordered a new abs valve block to switch out if the new master doesn't work or I'll return if it does.. I isolated all four corners yesterday in 2 separate ways and never got a good pedal. First I used a scan tool to shut all of the inlet valves on the abs block one by one which would basically lock the line to that wheel at the ABS. Then I used a line clamp at all four corners. So everything post ABS was ruled out. Then I pulled the master cylinder and it was full of air again.
I do have one guess related to the ABS system. Actually two guesses.
1. An internal leak in the ABS block.
2. And this one depends on if your model year has TCS, the traction control system. Your original post referenced dragging brakes. The TCS is a rather complex system, utilizing various sensors including a yaw sensor, each wheel speed sensor, and so on. If it detects one wheel losing traction and spinning, it will lightly apply the brake to that wheel, sending power to the wheel with traction. It also does this to keep the vehicle straight, such as black ice. It can make these minor break adjustments multiple times a second, and when working it works fantastic. It's actually utilized on all class 8 heavy duty trucks these days. This goes back to your first post about dragging brakes. If the system were to malfunction it could inadvertently create that symptom. My first inkling would be the ABS block with all the valves..... As in guess number one above... But if your model year has the TCS, it gets more convoluted as you have to consider a bad sensor, or the ECM itself. I would assume somewhere in a Tech 2 it could diagnose it.
1. An internal leak in the ABS block.
2. And this one depends on if your model year has TCS, the traction control system. Your original post referenced dragging brakes. The TCS is a rather complex system, utilizing various sensors including a yaw sensor, each wheel speed sensor, and so on. If it detects one wheel losing traction and spinning, it will lightly apply the brake to that wheel, sending power to the wheel with traction. It also does this to keep the vehicle straight, such as black ice. It can make these minor break adjustments multiple times a second, and when working it works fantastic. It's actually utilized on all class 8 heavy duty trucks these days. This goes back to your first post about dragging brakes. If the system were to malfunction it could inadvertently create that symptom. My first inkling would be the ABS block with all the valves..... As in guess number one above... But if your model year has the TCS, it gets more convoluted as you have to consider a bad sensor, or the ECM itself. I would assume somewhere in a Tech 2 it could diagnose it.
