Mechanics

CHEVY BRAKES FADE AND FEEL SPONGY AFTER BLEEDIN

1992 Chevrolet Blazer

Brakes problem
1992 Chevy Blazer 6 cyl Four Wheel Drive Automatic 200000 miles

Started with brakes feeling very spongy and not braking well and uneven. Replace master cylinder, filled and purged MC, installed MC and bled all wheels until new fluid came out. Didn't make any difference. Bled again about 3 times on each wheel, still no difference.
Can the ABS MC be bad or any other way to purge ABS system? Pedal will get spongy and go to the floor if hard pressure applied. No leaks that I can see, fluid doesn't get low. Visually inspected all brakes on all wheels and didn't notice any funny business, but then again I'm not a pro either.
could I still have that much air in the lines that isn't purging out?
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Lytesp33d
September 29, 2010.




If you want just crack all the bleeders open and just wait for a bit. Maybe 30 minutes and just keep the reservoir full at all times. Close them and see how it goes.

Does vehicle stop better now that you replaced all that?

Put as much brake force as required to make a complete stop and thats it! Put on alot of force and the pedal will sink. Perfectly normal. Shouldnt go down with just average braking force tho.

Blackop555
Sep 29, 2010.
I've bled the brakes even more, gravity bled, vacuum bled with little handheld pump. Can't be anymore air left if that's what it is.

Made no difference, I tried another brake booster thinking maybe a vacuum leak in booster, exactly the same result

I don't think the brakes feel spongy like they did before, but now that I have been playing and testing them, it almost feels like the pedal doesn't go down fast enough or it's too stiff and sluggish. Like you can't get it to move fast enough stop quick enough. You can mash the pedal or apply steady firm pressure and you get about the same stopping force. Hard as I try, I can barely get one tire to almost lock up and I don't think it's the abs working because it's smooth. I'm believe if the abs is doing it's thing, the pedal and the brakes would vibrate or do something similar.

I may try to completely eliminate the abs and have the lines go straight from the master cylinder to the wheels, with maybe a junction block in between. That way I would know for sure if it's the abs module not working correctly or bleeding pressure somehow.

Tiny
Lytesp33d
Oct 3, 2010.
To bleed the abs hcu youll have to have a shop do that. Too risky to be jumping pins in the module for you to be doing that.

Disconnect the wheel speed sensors and abs module connector and see if problem goes away. Abs could be " missfiring" thinking a wheel is locking up and not giving you pressure.

Try tapping on all the junctions while bleeding it to jar air loose and see what happens. Maybe retake off master and start over bench bleeding it. Make sure the hoses go right back into resevoir and under fluid untill no more air comes out with it pumped.

Blackop555
Oct 4, 2010.
I can jump pins easily (and safely) if I knew which ones to bleed the abs.

Tiny
Lytesp33d
Oct 6, 2010.
Ok. Is the vehicle equipped with EBC4 type antilock, does it have traction control?

Need that information first.

And lastly jumping may not work as you cant cycle the valves fast enough by hand.
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Blackop555
Oct 6, 2010.

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