83' z28 4wheel disc


my brakes never worked that well... the car stopped like crap..

sooo i replaced my master cylinder and bled the system completely...

NOW. when you hit the brakes the peddle goes down and makes a slight hiss, the rear wheels DONT stop(brake light comes on).. i jacked up the rear end and put it in gear, hit the brakes and the rear wheels still turn.. now i hit the brake peddle 2+ times the rear brakes work(brake light turns off).

the peddle does not go to the floor at anytime

Overall the car doesn't stop well at all! i have to keep pumping the brakes till finally they work.. i'm pretty confident i bled the system fully and its not the master cylinder..

i'm kinda thinking proportional valve?? or booster??

do any of these symptoms match with those??

 

Well i thought initially that the hissing sound was the brake booster, brake boosters typically do that when they are going south. There is a check valve on the booster as well, a very audible hiss isn't a good thing. Keep in mind there is a difference between the sound of a normal peddle and a hissing sound when you hold down the peddle, thats the booster. How old are those calipers?
In my experience** usually when you have a sinking peddle that just hits the floor with no resistance its the master cylinder, a really spongy pedal is usually that you have air leaking into the system. Hydraulic pressure is a result of a noncompressible fluid being pushed (by your foot) and it exerts a force on the caliper which then grabs the rotor. When you have air bubbles, they compress, so instead of the fluid transfering the force, it uses the energy to compress the air and makes it feel spongy.
- Check for leaks
- Check the check valve and booster
Also, what method are you using to bleed the system, its very important to not any air back into the system. What i normally do is get some vacuum hose and insert it totally submerged into a clear bottle (soda, gatorade) of brake fluid. Loosen the bleeder screw, have someone pump the brakes 3-4 times, and open the screw, when the fluid drains out into the bottle i close the screw before the pedal sinks all the way to the floor. You will see bubbles, and keep checking the fluid level in the reservoir constantly. Eventually, you will get just fluid, continue a few times more and then move on to the next wheel.

 

Sounds to me like you didn't "bench bleed" the master cylinder before you put it on.

If you look at the shape and location of parts, you will notice that there is a whole bunch of master cylinder that is located above the lines and above the fluid refill port. Therefore, if you put it on the car and there's air in it, you can bleed the brakes for a week and use 50 gallons of fluid, and that air will STILL be in there. It will NEVER COME OUT as long as the cylinder is in its installed position. The ONLY WAY to get it out, is to bleed it in the horizontal position BEFORE you install it; and MAKE SURE you don't let ANY air into it during the install process.

 

I did bench bleed the MC and i was extremely carefull about not letting air into it during the install.

and i believe i bled the system correctly. i started from the furthest wheel from the MC pumped 3-4 times and held it, my dad open the valve then closed then i let off the peddle

we spent a lot of time on each wheel just to be sure, there were no bubbles at all.

my calipers are as old as the car 1983

and the hiss sounds like its coming from the peddle not the booster, its hard to hear, so i guess its normal

i kinda think its the combination valve?
what are the symptoms of a bad valve?

but i will bleed the rear brakes again just to be sure

 

Also i've been calling part stores everywhere. I even called the local GM parts department and NO ONE has this damn proportional valve.. it's been discontinued, ANYONE know of what i can do??

such a headache lol

 

Call Dal:

Dal Slabaugh
Van Devere Pont-Buick-Olds
877-448-5451


Ed

 

finally took it to a mechanic.. It was my rear calipers!! the rear calipers are connected to the E-brake(my ebrake has been disconnected for a while).. apparently the calipers have some sort of a ratchet system on them connected to the ebrake.. and the ebrake holds the ratchet system in a certain place but since my cables are not connected it takes 2 pumps of the peddel for the piston to reach the rotor.. If that makes any sense lol, its hard to explain

anyone know of anywhere ican get new rear calipers with the ebrake system on them?

 

Might want to hook the parking brake back up. And your old calipers may not be bad, either. Read on.....

The e-brake being attached to the brake adjuster could very well be your problem. Using the e-brake is what ADJUSTS your rear clipers for wear in the brake pads so that they are always close. Not having the e-brake to do this "automatic adjusting" is why the mechanic found what he did and why you had to pump the brakes twice to get them to even engage.

Does that make sense the way I said it?

 

the e-brake is connected again, but the mechanic said something about the ratchet system on the calipers being frozen.

if i drive with the ebrake pulled up, the brakes work AMAZING.. (the ebrake alone doesnt lock the wheels).

if i drive with the ebrake down, only the front brakes work..

he said i need new calipers because the ratchet system wont losen up

and the ebrake is adjusted to go as tight as it will go so its not that

 

Probably rusted up now from years of lack of use - sorry.

 

Frozen rear calipers...rebuild them with a recall kit or swap to better PBR rear brakes.

Ed