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Discussion Starter #1
I have a question about the brakes on my 80 El Camino. I have a quick performance 9" rear with disk brakes, new proportioning valve for all wheel disk set up, new master cylinder and booster. I have bench bled the master before putting it on and let the system gravity bleed. I also had my wife help me pressure bleed today with the same results. When the car is off it has a somewhat firm petal. But once I start the engine it has no pressure to the petal at all, and doesn't want to return. Any suggestions will be greatly appreciated.*

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The "somewhat firm" pedal comment makes me think air is still hiding somewhere, but the no pressure and no return with the engine running sounds really strange. Do the brakes hold while the engine is running? Do they hold with the engine off? I mean will it stop the car? Also, what kind of booster did you get? I'm suspecting that something might not be right in the booster. One more thing, the pedal returns with the engine off right?

Joe

Joe
 

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Discussion Starter #3
The car is on jack stands currently. So im not sure if it will stop the car. I'd guess that with no power it will but once the engine is running I'd say no. The petal returns with no power. The bake booster is supposed to be a factory replacement. I have a few things to check on in the morning. Maybe a good night's sleep will help.
The "somewhat firm" pedal comment makes me think air is still hiding somewhere, but the no pressure and no return with the engine running sounds really strange. Do the brakes hold while the engine is running? Do they hold with the engine off? I mean will it stop the car? Also, what kind of booster did you get? I'm suspecting that something might not be right in the booster. One more thing, the pedal returns with the engine off right?

Joe

Joe
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Sounds like a plan, a good nights sleep is always the best solution! I still think something is not right in the booster. Good luck! And hopefully someone else has better info!

Joe
 

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Just went through this on my mustang. Turns out the wheel cylinders in the rear were bad and sucking air into the system.

There was no evidence of fluid leak at all. the fluid level in the master cylinder even looked ok. i was 100% certain it was the master cylinder and replaced it. 2 days later same issue. it wasnt until i pulled the drums that i saw the slight leaking. what is happening is the wheel cylinders are actually pulling air into the system. the air is getting stuck in the line and thats why the level doesnt seem to drop.
 

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Just went through this on my mustang. Turns out the wheel cylinders in the rear were bad and sucking air into the system.

There was no evidence of fluid leak at all. the fluid level in the master cylinder even looked ok. i was 100% certain it was the master cylinder and replaced it. 2 days later same issue. it wasnt until i pulled the drums that i saw the slight leaking. what is happening is the wheel cylinders are actually pulling air into the system. the air is getting stuck in the line and thats why the level doesnt seem to drop.

Does rear disk brakes have wheel cylinders ?
 

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few thangs id double check
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I cant really tell what I'm seeing in the new rear end pic, its kinda blurry,,
but if you swap sides on the calipers ?? the bleeder will be on the bottom ..
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on a dry brake system
iv found sometimes a mix of pressure and vacuum bleeding works real well..
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I believe some have had to check the brake rod length when going to a disc/disc master cyl..
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is the new proportioning valve in right ?? front to front / rear to rear ??
there usually different size lines tho..
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:texas:
 

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Discussion Starter #9
So I have gone through the entire system again. I checked for adjustment of booster rod. It has no adjustment. Made sure no air was trapped @ master cylinder and proportioning valve. Proportioning valve has been swapped for disk/disk. Contacted Quick Performance for brake bleeding procedures. Pulled rear callipers to bleed out any possible trapped air pockets. And gravity bleed entire system again. I have gone through about 192 oz of brake fluid trying to figure this out. After rear brake adjustment I do have a firm petal when engine is off. But when engine is on it's spongy. On jack stands it will stop rear rotors in gear with foot all the way to the floor. Oh another thing I tried. When engine was on I pulled vacuum from booster and plugged the booster with my finger and my wife said petal was more firm after a few pumps.

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if you swap sides on the calipers ?? the bleeder will be on the bottom ..
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Don't know what calipers you have but some will mount on either side but, if on the wrong side, the bleeder will be on the bottom of the caliper and will NOT let the air out.


Easy enough to check to see if the bleeder is at the top of all calipers.
 

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Discussion Starter #12
Ok, I think I'm good with the brakes. I put the wheels on and set it on the ground. Did some test runs in the yard and all 4 seemed to leave the same distance of marks in the yard lol. So I think my issue was the rear brake adjustment that quick performance suggested. It was allowing to much travel before the pads we're making contact with the rotor. The petal still seems softer than all of our other cars, but it stops pretty good, ie: slung my laptop off the bench seat when I hit the brakes. Thank you everyone who helped out!

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