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  #1  
Old 02-02-2013, 12:14 PM
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Question Soft Brakes w/ the Engine Running

You Chevy guys were awesome last time I posted.
Hopefully you guys have another trick up your sleeve.

I'm working on a major Brake issue:

1996 Chevy Blazer LT 4.3L 4x4

This problem is, when the engine is running, the brakes are extremely soft. Closely hit the floor. There is stopping power, but not nearly as much as there should be. If you step on it hard enough, you will hit the floor w/ little effort. I do have a brake light on due to the ABS Speed Sensors being Boogered. (frayed wiring) When the engine is off, the pedal will stiffen up to a normal tight w/ a full flow of brake fluid coming out of All Four Bleeders.

Now, I do hear a slight squeak coming from somewhere between the pedal & booster but I got the same slight squeak in my Dodge but it doesn't affect anything. Perhaps that's very different w/ a Blazer.

I've done replaced the Master Cylinder since it was fairly cheap. I also put another ABS unit it. The other ABS unit, (same as this one) has Bleeders on it. The old ABS unit didn't seem to do anything when I opened the Bleeders. This one I will hear air squeaking through when I open them up but no fluid will escape no matter how much the pedal is pumped, just air.

Once again I've made a fairly large order from RockAuto. I'm replacing both Calipers, Splash Shields/ABS Speed Sensors, Hydraulic Hoses & Brake Lines throughout the Blazer. I'm replacing all the Brake Lines & Hoses because they're seriously rusty, No Leaks but still no good being seriously rusty. Everything in the Rear minus the Hydraulic Center Hose is brand spanking new & spooned up correctly since I had to replace the Rear Differential.

Now, I've got No Fluid Leaks Anywhere & the pedal feels perfect when the engine is off. I even, (just for the heck of it) checked to make sure everything was grabbing & releasing correctly. It all checked out normal. I have also replaced all the Vacuum Lines on the Booster in the last project, plus the Check Valve. They were all dry rotted & leaking. All is in check now.

Any ideas why the pedal is so soft & nearly touching the floor when the engine is running?
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Old 02-02-2013, 12:40 PM
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You have a vucume leak ,could be the power brake booster leaking internaly..I know you mentioned it but its all i can think of.
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Old 02-02-2013, 01:24 PM
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since you have replaced so much having to do with the brakes, you could have a bubble in there somewhere. try to re-bleeding the brakes again, i know its a pain, but i had the same problem when i replaced my rear brakes on my old 95.

i dont know if i read this correctly or not, but when you were bleeding the ABS unit, i am assuming that you are closing them when you are pumping the pedal....
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Old 02-02-2013, 01:50 PM
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Yeah... I should have explained that a bit better Twip. Sorry about that. I tried bleeding the ABS Unit like the Calipers & Drums. Pump it up... Let it spit until the pedal hits the floor. I did that w/ the ABS. But, its weird, cause the pedal wont go down when you open the bleeders on the ABS like on the calipers & drums. It does nothing... just i tiny tiny bit of air when you apply pressure to the pedal. And, I've done bleed so many times I've lost count. Wasted four big bottles of fluid. I'm getting full steady streams of fluid from all bleeders. Not even a tiny air spit, just straight fluid. And 1sttimejimmyowner, you've kinda seconded a thought of mine. It is possible that Booster is leaking Internally but I surley hope not. Thats not a cheap replacement by any means. And if it is an air leak, its definatly the Booster, cause all the air lines are in check, no hissing noises, I've also sprayed everything w/ soap water looking for bubbles. Nothing
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Old 08-15-2013, 12:51 PM
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i hope is not too late to reply but i had major issues bleeding my brakes after the lines rusted through,, until that is we did it with the truck running,,, silly i know!! btw there is special procedure and scanner tool to work on the abs .... try bleeding with the truck running,, weird yes but it worked for me!!
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Old 08-16-2013, 05:45 PM
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Did you ever get this figured out? was it the booster? I've got an '01 doing the same
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Old 08-24-2013, 12:31 PM
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No, I never did fix it but I did figure out the ISSUE.
I replaced everything.
Swapped ABS Pumps,
ABS Sensors/Splash Shield
Both front & single rear Hydraulic Hoses
All Steel brake lines
Calipers
Compressors
Bleeders/Rings/Bango
All hardware
Master cylinder & Booster
I'm so sick of hearing about still having air in the lines when I've done bleed them all a million times, lost $$$$$$$$$$ in brake fluid, not one little spit of air anywhere.
Although yes I know what the problem is & this is only a personal thing because I'm ready to burn this Blazer due to all the problems & $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$.
That abomination called a ABS Pump!!!!!!!!!!!!
You need a special one of a kind extra pricey computer that will open the valves in the ABS Pump itself while bleeding.
F%@% THAT
I am not yelling at anyone or discouraging anyone from anything.
This is simply my current attitude about my own Blazer.
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Last edited by PhilBilly; 08-24-2013 at 12:44 PM.
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Old 08-25-2013, 12:33 PM
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i did wonder if the issue might be in the ABS pump.... hoping not - guess I'll decide then if i really need ABS - might bypass it and have to use good 'ol threshold braking.

If I figure out a......different way of opening those valves without a computer I'll post back - got a spare module kicking around so I might see if i can access and power the valves directly

Thanks for the info!
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  #9  
Old 08-26-2013, 06:35 AM
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Bypass... I hope it works for you. All I know is, without the ABS Pump functioning, this (mine) Blazer likes to eat Caliper Pistons thus blowing out the Caliper all together. Always a slight pull when braking. It's only a personal thing, but I've never had so much trouble w/ brakes in any vehicle. But then again I've never came across ABS Pumps like these either. I have a Pump/Proportioning valve in my Dakota, when I bleed it, it will be a douche on the first round or two of bleeding but thats it. Like anyother vehicle, eventually they will cooperate after skinned knuckle & alot of cussing it out, but not these Blazers. I won't discredit Chevy because they do make alot of dependable vehicles however they dropped the ball on these "so-called" better braking systems.
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Last edited by PhilBilly; 08-26-2013 at 06:38 AM.
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  #10  
Old 08-26-2013, 08:43 PM
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All of the bleeding in the world, gravity or pressure, will not remove the air from the ABS unit. The pedal will be low & mushy until the automated bleed is performed, (2 minute job with a capable scan tool). The automated bleed is the ONLY way to remove air from the ABS unit after replacement of the master cylinder, ABS unit, or the lines that connect the two together. The automated bleed operates each of the apply and dump valves, in the proper sequence, in the ABS unit. This forces the trapped air into the brake lines. After the automated bleed, each wheel must be bled as usual at each bleeder.
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Last edited by Captain Hook; 08-26-2013 at 08:47 PM.
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Old 08-26-2013, 08:43 PM
 
 
 
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02, 1998, 98, blazer, brake, brakes, breaks, chevy, drum, engine, gm, problem, running, soft, spongy, weak


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