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ABS unit blocking flow of brake fluid, 95 silverado 2wd

This is a discussion on ABS unit blocking flow of brake fluid, 95 silverado 2wd within the Technical / Maintenance forums, part of the General Discussion category; Hello, I'm just wondering if any of you guys have ever encountered this problem, and if so, what you did ...

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    ABS unit blocking flow of brake fluid, 95 silverado 2wd


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    Hello, I'm just wondering if any of you guys have ever encountered this problem, and if so, what you did to solve it. My ABS pump is blocking the flow of fluid to my right front caliper. It's been sticking on and off for the last 4 years, but never bad enough to stop me from driving it. (I replaced the calipers previously, but soon realized that wasn't the problem.) However, the day before yesterday, it started to do it so bad that I said enough is enough. The wheel got so hot driving around town that I could feel the heat just walking over to it. So yesterday I fllushed out the whole system until the fluid coming out was clear, which took about an hour and a half, but that made it worse. Now that caliper won't even apply. I verfied that the obstruction is in the ABS unit by disconnecting the line to that caliper from the ABS and stepping on the brake, it feels like the line is still connected, pedal doesn't sink down, and hardly any fluid even comes out. Strangely enough, I was able to bleed that wheel earlier, although I did observe that it seemed to take forever to get the old fluid out. I don't know if there is something in there clogging it, or if one of the internal valves is stuck in the wrong position, or what. I took the truck out in the country and made the abs activate on a dirt road repeatedly, but it wouldn't open back up, even with the new clean fluid. I didn't use any type of equipment to flush the old fluid out, just loosened the bleeder nipples, put a hose on them into a container, and pumped fresh fluid through like normal.

    Any ideas? What do I do? Can I dissassemble this piece of **** myself and repair it? (have any of you guys done that before?)

    Thanks for any info on this..

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    GMC RULZZ NEUMANNZZ's Avatar
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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    maybe get a used one to practice on.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    It could be the brake line is collapsed.

    I pulled my 92 out of storage last fall with a sticking caliper, so I came prepared with two new ones. Couldn't bleed the driver's side at all. Pulled the brake hose back off the caliper and could STAND on the pedal and get maybe 1 drop of fluid every 3-5 seconds from the end of the brake line. New lines, good as new. Just something else to check, and it's fairly common.

    92 K1500 WT - Gone
    92 C2500 - Current. Scottsdale, 350tbi, 4L80E, 14 bolt sf

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    Quote Originally Posted by adam728 View Post
    It could be the brake line is collapsed.
    Thanks for the reply, but if you look at my post again, you'll see I wrote, "I verfied that the obstruction is in the ABS unit by disconnecting the line to that caliper from the ABS and stepping on the brake, it feels like the line is still connected, pedal doesn't sink down, and hardly any fluid even comes out", so the brake line from the abs to the caliper is out of the equation.

    I got a quote of $560 for this thing, I don't want to pay that. I should be able to fix this myself, there isn't much I can't do. But I'm rapidly losing hope on that, as I have a factory service manual for another GM vehicle of mine, and it gets into Everything, but says the abs pump should never be disassembled, just replaced, and has no info about anything inside it.
    Last edited by rorik; 05-28-2010 at 08:45 PM.

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    GMC RULZZ NEUMANNZZ's Avatar
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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    if your in san diego you can get one for cheap at ecology or pick a part.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    The ABS unit contains the proportioning valve. The prop valve contains a safety device so that if you blow a hose/line, it will shut off flow to that circuit. Basically it works by comparing the flow between the two circuits (front and rear). If there is a large variance, like you would have with a line failure, it will shut that circuit off.

    To reset the valve, you need to STOMP on the valve. Like if you were doing a panic stop.

    But you need to fix the sticking caliper first. I would guess that the flex hose is bad, and working like a check valve. It's a pretty common problem.

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    Quote Originally Posted by rorik View Post
    Thanks for the reply, but if you look at my post again, you'll see I wrote, "I verfied that the obstruction is in the ABS unit by disconnecting the line to that caliper from the ABS and stepping on the brake, it feels like the line is still connected, pedal doesn't sink down, and hardly any fluid even comes out", so the brake line from the abs to the caliper is out of the equation.
    Whoops. I read it as the line was removed at the caliper. My mistake.

    92 K1500 WT - Gone
    92 C2500 - Current. Scottsdale, 350tbi, 4L80E, 14 bolt sf

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    The Good Samaritan
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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    have you tired to bleed the ABS module itself? should be a bleeder on the top of it.
    1995 K1500, ECSB, 350TBI, 4L60-E, 285/75/R16

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    Quote Originally Posted by d_johnsen View Post
    have you tired to bleed the ABS module itself? should be a bleeder on the top of it.
    That would be nice, but I have never seen one.

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    Well, I solved the sticking problem! No one thought I could do it, so I did. Haha. I took the ABS pump apart, there were these little solenoid valve things inside it, and the first 3 had little tiny screens on the top, just like a fuel injector. Well, lo and behold, one of them was totally clogged with some type of crap. It looked sort of like tiny, tiny pieces of shredded up paper towel on the screen. I took that off, sprayed the whole thing out with brake clean, keeping everything as clean as possible of course, and now I have fluid to all of my wheels again.

    Now I just need to figure out how to bleed the damn thing. The Haynes manual I have is of course completely worthless, it doesn't get into any of this at all. Bleeding the brakes the normal way does not get all of the air out, there is some other way to do it. I found a spring loaded valve on the side of the abs pump, when you push on that, fluid comes out, but it doesn't get all of the air that is trapped in it. The truck is driveable, but the pedal sinks down way too far for my liking. Hopefully I'll figure this out tomorrow.

    Any of you guys have any tips on bleeding the system after replacing the abs pump, let me know! I'm guessing it has something to do with what's behind those 2 little caps on the front.

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    Glad you found the problem. I'll add that to my list.....

    The correct way to bleed the ABS is to activate all the ABS valves with a Tech II scanner. That'll run you about 5 grand. Or you can take it to a shop with the correct equipment.

    Some guys have report success bleeding the ABS module by driving on gravel roads and stomping on the brake pedal to activate the ABS.

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    I tried the gravel road thing, but it didn't make the pedal any better. I didn't think it would, but it didn't hurt to try, I guess. I'll go talk to a guy who owns a shop down the street.

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    I guess I failed to mention you need to re-bleed the lines after activating the ABS. Are your rear brakes adjusted up nice and snug?
    Last edited by 2COR517; 05-29-2010 at 07:09 PM.

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    Re: ABS unit blocking flow of brake fluid, 95 silverado 2wd

    This is an old post, but I wanted to know if you (rorik) were able to bleed your abs pump. Also, what did you do to take the pump apart? I'd like to try it with mine too.

 

 

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