Let me start by saying I appreciate all the info in your tech section and threads. This is my first post but I've been searching and browsing on here for about a week straight and have solved most of my problems with your info.

I bought this truck, '99 blazer 4x4 2 door, about a month ago. Been working on it nonstop, bought it with a new rear brake line but it wasn't bled as the previous owner snapped off both rear bleeders when trying. I put new calipers on, bled the brakes the old fashioned 2 man way, and my pedal was pretty stiff. Then I started the truck, and the pedal just goes straight to the floor almost effortlessly.

That was yesterday, so I made my whole day dedicated to getting these things done. I gravity bled today, in about 20 minute increments, one wheel at a time, starting back right and working around. Repeated this process for around 8 hours. Now the pedal is ROCK HARD when the truck is off, but again when you start the engine, the pedal is very soft. It did show some improvement, but still very soft in my opinion.

The only other symptom I could find is the ABS setup by the master cylinder has some sort of valves with rubber caps on them, one by the firewall and one facing toward the radiator. The one facing the firewall pops open as soon as the pedal gets any kind of decent pressure, like it's a pressure relief valve of some sort. I put a pry bar on it and had my helper press the pedal, and we got some good results by holding the valve thing in.

I came across this photo on here earlier when doing some searching.
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I was wondering if something like this is safe? The guy said it worked for him, but I plan on selling soon (long story, baby on the way) and I don't want to have it on my conscience thinking I might put someone in harms way. Any other input is more than welcome. Thanks for your time guys.

 

The rubber caps protect the ends of the centering valve, (proportioning valve, safety valve) whatever you choose to call it. The purpose of the valve is to shut off a failed hydraulic system so the remaining system can build pressure and stop the vehicle. It will illuminate the red brake light on the dash and the pedal will drop down. The valve pops the cap off because it is trying to shut off a system. There's either a leak or an air bubble trapped somewhere. The valve will have to be manually centered, (special tool) to bleed the system. After you get the problem fixed, you should perform the automated bleed and manually bleed each wheel afterwards. The automated bleed forces all solenoids in the ABS unit to bleed any air out, into the lines. Procedure must be done with a capable scan tool.

 

Thanks for the quick reply. I don't get the red brake light at all since I've bled the brakes. My abs light is staying illuminated though. I don't have the means to get the truck to a dealer for the automated bleed, but I did find a used abs unit for $50 locally.

Is this likely just in need of bleeding, or is it a sign of abs unit failure? I have a bad habit of throwing parts at problems when it comes to ABS nonsense like this. Would it be a wise gamble to install the new unit and pray I don't get air in that one during installation?

 

Have you tried bleeding it with the truck running? Some times that helps. Maybe the MC took a crap. Also does the pedal go to the floor when you crack the bleeders?

 

Yep tried the 2 person method with it running. At first I thought MC too but it doesn't have any give with the truck off. The pedal will go to the floor when you crack the bleeders. Been keeping it off the floor best I can so I don't overextend MC piston. I have a feeling my problem has to be in that stupid ABS unit.

I had a nice hillbilly thought. What if I take the thing in the backyard and lock up the wheels a few times, try to get the solenoids to fire and shove the air that's stuck in the ABS unit into the lines, then bleed the lines again. Worst case scenario I go through another bottle of brake fluid and have some fun. Will the ABS kick in if the ABS warning light is on?

 

Hillbilly thought....is pretty accurate No, that will not work. If the ABS light is on, it means the ABS system is disabled due to a problem with it. The bleed procedure systematically opens certain combinations of valves in a certain order. It's done while the engine is running: you put a foot on the brake pedal and keep pressure on it during the bleed. After you initialize the bleed, the EBCM does the rest... takes about 30 seconds to complete. Replacing the ABS unit requires the automated bleed. It's impossible to replace the unit without introducing air into it.

Manually center the valve and gravity bleed each wheel, keeping the valve centered the entire time. Then do the two man bleed at each wheel: push the pedal down once and hold, then open and close the bleeder. Repeat for each wheel until no air is expelled during the two man bleed. Make sure the master cylinder is full during the entire bleed process.

 

just an update, I got a hold of an old friend who works at a nice shop, hopefully he can borrow a scanner and we can run the automated bleed at my house. I'll let you know how it comes out.

 

Also, pretty bummed I can't justify sliding around in my backyard. Theres a whole acre of empty, hidden space just begging for a blazer to rip it up.