Brake system help!

Discussion in 'Engine Performance + Maintenance' started by JJ Burgess, Apr 19, 2019.

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  1. JJ Burgess

    JJ Burgess Newbie

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    Hmmm. I’ll have to give that a shot. I ditched the vacuum bleeder and did it the old fashioned way. Bled a quart of fluid and got all the air out. Was getting most of the air from around the bleeder hose. Still not getting good pressure. I think I’m going to go and get a new OBS master and see what happens. What is the best quality to get? I gotta figure something out. I took the RWAL out because I thought that might be it. Not the case.
     
  2. RawbDidIt

    RawbDidIt I'm Awesome

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    https://r.tapatalk.com/shareLink?ur...&share_tid=43840&share_fid=40934&share_type=t

    ^this has the information you're looking for

    Sent from my SM-G965U using Tapatalk
     
  3. JJ Burgess

    JJ Burgess Newbie

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    Hmmm. So. Unless I upgrade the calipers I’ll just go back to the original master cylinder. I just want my brakes back lol. I’ll just leave the RWAL out. Never worked anyway plus it’s pointless to have just on the rear. I’ve never bled so much fluid in my life. I’ve been trying to find a factory combination valve but I can’t find one. Anyone know where I can get one?
     
  4. JJ Burgess

    JJ Burgess Newbie

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    So what is the difference between getting a master cylinder with heavy duty brakes or just the standard? Would that help me get a stiffer pedal?
     
  5. Schurkey

    Schurkey I'm Awesome

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    Low, squishy pedal? If you didn't tilt the master cylinder, you most likely did NOT get the air out. Air is probably still trapped in the master cylinder. Bleeding at the wheel cylinders will not release that air no matter how many gallons of fluid you run through the system.
     
  6. JJ Burgess

    JJ Burgess Newbie

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    Ok. So to do this. Jack up the rear as far as possible and then open the master cylinder lid and just tap the brake pedal? Just want to make sure I’m understanding it correctly.
     
  7. Schurkey

    Schurkey I'm Awesome

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    Verify you have adequate fluid in the master cylinder.

    Jack up the rear until the master cylinder is AT LEAST level, preferably down in front. If you can't jack the rear high enough, you'll have to pull the master off of the booster and push the front down--then move the piston with a blunt object (wood dowel or Philips screwdriver). DO NOT DISCONNECT THE BRAKE TUBING.

    Open the master cylinder lid--or not. Your choice. If i had a helper, or I could see it from the driver's seat, I'd want to see bubbles. If I didn't have a helper, I wouldn't bother.

    Tap brake pedal MORE than what's required to take up all the slack in the linkage between pedal and booster, and between booster and cylinder. You have to move the primary and secondary pistons at least a little. Going farther than that is pointless, because the piston seal covers the bypass port. It may be that the air bubble ahead of the primary piston will have to bleed out into the reservoir before the secondary piston will start to move. Then the secondary air bubble will blow into the reservoir. When there's no more air, you'll see two little "geysers" of fluid (not air) pushing up from the bypass ports when the pedal is tapped. You'll see these same "geysers" with the vehicle level and the master tilted upward--but there could still be air ahead of the ports. That's why you have to tilt the master DOWN in front to release the air.

    Tap the brake pedal multiple times. If you're watching the reservoir, you'll see when there's no more air. If not, you just have to tap and hope.







    There was a time--thousands of years ago, when Dinosaurs roamed the Earth--that master cylinders had their own bleeder screws, and then all this crap wasn't needed. 'Course, bleeder screws cost money, as does drilling and machining the casting to accept them, so bleeder screws on the master disappeared a long time ago.

    You've never said whether you bench-bled the master cylinders before installing them. SOMETIMES bench bleeding will eliminate this problem--depends on how carefully you bench-bleed, AND how careful you are to seal the ports during the installation, AND how fast you can connect the brake tubing once the thing is bolted on. Tilting the master cylinder like I've told you, because bench-bleeding wasn't enough, is really common.
     
    Last edited: Apr 20, 2019
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  8. JJ Burgess

    JJ Burgess Newbie

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    Ok. I’ll give that a shot. My truck already sits lower in the front so I should be able to to get it high enough. I’ll let ya know what happens. Thanks for the advice.
     
  9. doug_95c1500

    doug_95c1500 Newbie

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    I couldn't find a part # for the combo valve anywhere, so I took my old one off, and compared it to others I looked up on a Google image search. I ordered this one from Amazon:
    ACDelco 172-2069 GM Original Equipment Brake Combination Valve

    It was mounted backwards on the bracket that didn't fit anyway, so I took it off the bracket and put it on my original bracket. I also deleted the RWAL system, and bench bled the new master cylinder. I have a firm pedal now, but I don't think the brakes have just a lot of power, I just don't know what they should feel like cause they were horrible when i got the truck.

     
  10. JJ Burgess

    JJ Burgess Newbie

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    Awesome. Thanks for the info! I can’t find the combo valve anywhere. I can’t believe with all these trucks on the toad that they’re not available.
     

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