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Spongy brakes - 1994 K2500 with ABS

This is a discussion on Spongy brakes - 1994 K2500 with ABS within the Technical / Maintenance forums, part of the General Discussion category; Hello all, I have searched all the posts for spongy brakes, and it looks like there are about four causes: ...

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    Spongy brakes - 1994 K2500 with ABS


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    Hello all,

    I have searched all the posts for spongy brakes, and it looks like there are about four causes: ABS proportioning valve, rear drum brakes not adjusted properly, master cylinder bad, or brakes need bled.

    I bought new self-adjusters for the rears and adjusted the rear drums properly. Not much change.

    I am curious about this proportioning valve. I do have ABS, and I am assuming this proportioning valve is not directly under the master cylinder? The ABS modulator is directly under the master, and has only the REAR brake lines passing through it. I believe the proportioning valve has both sets (front and rear) brake lines passsing through it, and it has the one wire attached to it that would illuminate your BRAKE light in the event of a problem.

    Has anyone found this proportioning valve other than at the dealer?

    Thanks!

    dgilfillen

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    Registered User ruger4d4's Avatar
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    Re: Spongy brakes - 1994 K2500 with ABS

    look on page 132 in the lmc online catalog hope this helps
    95 Z71 5.7 A/T, 03 Yukon 5.3 A/T

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    Re: Spongy brakes - 1994 K2500 with ABS

    Quote Originally Posted by dgilfillen
    Hello all,

    I have searched all the posts for spongy brakes, and it looks like there are about four causes: ABS proportioning valve, rear drum brakes not adjusted properly, master cylinder bad, or brakes need bled.

    I bought new self-adjusters for the rears and adjusted the rear drums properly. Not much change.

    I am curious about this proportioning valve. I do have ABS, and I am assuming this proportioning valve is not directly under the master cylinder? The ABS modulator is directly under the master, and has only the REAR brake lines passing through it. I believe the proportioning valve has both sets (front and rear) brake lines passsing through it, and it has the one wire attached to it that would illuminate your BRAKE light in the event of a problem.

    Has anyone found this proportioning valve other than at the dealer?

    Thanks!

    dgilfillen

    Might also consider new brake lines, they are pretty cheap, and as old as yours are, they need to be replaced.
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    Re: Spongy brakes - 1994 K2500 with ABS

    Did you mean I should replace the three brake hoses or the steel lines? All steel ones look fine, but I will consider the hoses.

    dgilfillen

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    Re: Spongy brakes - 1994 K2500 with ABS

    I also have a 94 and am the orig owner. Inspection will tell you if you should replace the hoses, not age. Rubber will "age" differently depending on your enviroment. My hoses are original but I have seen others that age in half this time.

    Hoses that are ready to fail will not cause spongy brakes. Your first step is looking for obvious wear or failures throughout system. Second step is making sure brakes are adjusted properly. Third step is a correct and thorough bleed of entire system.

    Any internal clogs or seperating rubber should be detectable during this process.
    The combo valve which contains the proportioning valve (and several others) has that single wire that trips the brake lite if the pressure front vs rear is going wrong. The brake light shows for three different conditions, and they are at different brightness levels.

    You never mentioned if you're getting the brake lite at any point, nor why you want to replace the combo valve.

    You do not have true ABS but rather RWAL -rear wheel antilock.
    Other than air in the valves, they will not cause spongy brakes.

    Hope this helps.
    In this pic, left to right, master,rwal valves, combo valve, rwal controller box.
    anything I say is probably wrong, see, you been told

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    AKA Slim Picks whitesilvy2000's Avatar
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    Re: Spongy brakes - 1994 K2500 with ABS

    it's been in my experience, spongy brakes usually leads to air in the lines, or a master cylinder that is on it's last leg.

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    Re: Spongy brakes - 1994 K2500 with ABS

    Crabtruck,

    Thanks for the advice. The reason I had planned on replacing the proportioning valve is that most of the forums had suggested that if the brake pedal was spongy, buildup of crap in this valve could cause it.

    One guy in particular had bled his brakes 10 times and could still not get a stiff pedal. He ended up replacing a dump valve (which could be the ABS modulator, not the proportioning valve).

    Is this only the case with 4-wheel ABS? I know I do only have RWAL, so you all feel this is most likely just a bleeding issue and not crap in the RWAL valve or prportioning valve?

    Can I get a good bleed without cycling the RWAL valve, or must that be done with a scanner that can turn on those RWAL valves?

    Thanks again!

    dgilfillen

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    AKA Slim Picks whitesilvy2000's Avatar
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    Re: Spongy brakes - 1994 K2500 with ABS

    I've never done it with a chevy, but the A2 VW's with the rear anti-lock, you just crack the line and have someone push the brake pedal and the pump kicks on then. This is with the key in the "run" position. I know this is like comparing apples and oranges, but who knows, maybe they are similar systems.

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    Re: Spongy brakes - 1994 K2500 with ABS

    Don't feel like the lone stranger.

    I've just completed a full brake job on my '94. Overhauled the front calipers, replaced all 3 flex hoses, new master and rear wheel cylinders, new rotors, new pads and shoes, got a new pressure bleeder (my old one died) and bleed the crap out of them, so now it's got all new fluid also (It would have any way).

    Engine off you can stand with both feet and all your weight on the pedal, SOLID!

    Start the engine, pedal goes to the floor.

    I've set the truck aside for a few days , and now have to get it on the road.

    A friend of mine had a 1990 K3500 with this same thing happen, only a shop had done the work, when the shop couldn't figure it out, it went to 2 different dealers by hook before someone fixed it. No, he dosen't remember (of course) what the fix was.

    Any thoughts would probably help us both.
    Last edited by mjwhoopie; 09-18-2007 at 11:43 PM.

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    Re: Spongy brakes - 1994 K2500 with ABS

    There is a different fluid action in the system with pedal bleeding vs pressure bleeding.
    I use the pedal and have fixed the problem on my 94.
    Turning the key on without doing anything else cycles the ABS valves
    is what I've heard but been unable to confirm.
    I would reccomend pedal bleeding with the engine on for this.
    The valves react at different pressures and the booster obviously changes the pedal effect.
    I have also left the rear bleeder open overnight and had a good result 12hrs later then full bled.
    Maybe that was just luck but it won't cost any money to try.
    Also at a point I disconnected the battery after the original bleeds to fix rear cylinder.
    Possibly this reset some electronic lock up in the ABS box.
    You could also check to see if disconnecting the ABS electrically and bleeding gives you different results.

    whitesilvy I have heard that reccomend for this truck but did not do that myself.
    Last edited by crabtruck; 09-19-2007 at 10:41 AM.
    anything I say is probably wrong, see, you been told

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    Blown95 blown95's Avatar
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    Re: Spongy brakes - 1994 K2500 with ABS

    I have the same problem with mine(95 Yukon). If you figure something out, let me know.
    1995 Yukon,Voilant CAI,MSD ignition,TBI spacer,Flowtech headers and y-pipe,Flowmaster cat back,electric fans,Trans-Go shift kit,b&m shift plus,R.V. Morse ported tb,3.73's

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    Re: Spongy brakes - 1994 K2500 with ABS

    Any other tips??? I also tried to bleed the brakes with the pedal and it still doesn't get as hard as I would like...
    Thanks, Joe

    1994 Chevy 1500 Suburban, 160,000 miles, stock TBI 350, rebuilt 4l60e w/stock dacco converter (rebuilt again on 10/10/07), Trango HD2 kit, Tru-Cool 4590 transmission cooler, 3.42 gears, 10 bolt rear....

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    Re: Spongy brakes - 1994 K2500 with ABS

    i think all obs brakes suck mine do and everything has been replaced.

 

 

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