Brake fluid not comming back to MC

[oldblue1968chevy]

My front brakes are sticking and not comming back to MC

I can crack the bleeder valve to let pressure off.

I can crack open the line from prop. valve to MC to release pressure.

I added power brakes ALONG time ago. At the time it was drum drum power brakes (booster was from a disc brake truck) I swapped all linkage and rod but didnt swap the actual brake pedel. Should I have?

I have new calipers....Mc is about 8 months old Booster is no telling how old possibly original.

Any ideas? Im tired of messing with it just to find out the next day my brakes lock up and im on the side of the road with the hood up. Everybody is giving me crap about it and telling me to take it to somebody...

[Test Pilot]

Is pressure released from the system if you crack open the line at the MC?
If you let it sit will it release on it's own over time?
If so then it would appear that for some reason the MC is getting stuck in the depressed position. This can be from a brake push rod that is out of adjustment, or maybe the MC has parts sticking internally.
Do you happen to have any soft/rubber lines between the master cylinder and the prop valve?

[fine69]

Sounds like the MC is bad.

[oldblue1968chevy]

no soft lines between mc and prop. valve. I reckon i'll be pulling mc off and swapping it lol.

dad belives it may be something in the lines??? But he doesnt have alot of knowledge on cars trucks...

Dunno about lettin her sit overnite..I gotta crack something open all the time to release pressure. i'll try MC tomorow lol

[Sammy]

Doesn't sound to me like a booster problem. Sure someone will lead you with more knowledge than I. But I would wonder about front brake hose internal failure blocking the return of fluid. Next I would be looking at the P/V or master cylinder. The brake pedal shouldn't have anything to do with your problem as long as you have the rod adjusted correctly.

[oldblue1968chevy]

Well, they dont stick right away..it takes 10 miles or so before they stick. Adj. May be off. Im guessing I need to adj. it so theres less pressure on the brakes? The brakes are FINE until I drive it awhile. Could brake fluid be getting hot and causing this?

[Test Pilot]

Originally Posted by Sammy

. But I would wonder about front brake hose internal failure blocking the return of fluid.

I've had this very same thing happen to me before, but typically the blockage is in the hose and since there is pressure contained upstream from the flex hose I don't think this is as likely, but shouldn't be ruled out.
A way you can check for m/c rod adjustment is to get the brakes such that they are stuck, then loosen the nuts holding the mc to the booster. If the issue doesn't go away, then you probably don't have to worry about the booster/push rod.
For the price of a new MC, it's kinda hard to go wrong.

[oldblue1968chevy]

Oh yeah I tried loosening Mc Booster nuts 9/16 (2) of em

Didnt do anything lol.

Reckon i would be able to get a trade in Mc (defective)?

[Test Pilot]

Originally Posted by oldblue1968chevy

Oh yeah I tried loosening Mc Booster nuts 9/16 (2) of em

Didnt do anything lol.

Reckon i would be able to get a trade in Mc (defective)?

So the problem is between the MC and prop valve. The two final checks I'd do with the info provided so far would be to crack the line at the MC, both of them. If no significant pressure is noticed, then I'd look more closely at a prop valve. However I suspect the MC is the issue.
As for return, it's up specific part warranty. My experience with the two main part stores here are that if you purchased it at Autozone, then they should have any warranty info at any store. Advance autoparts requires that you go back to the store you bought it unless you have a receipt. Advance doesn't share your purchase info on a corporate network like Autozone. O'Reiley is just moving into my area so I can't speak for them.

Good luck
Jason

[Sammy]

Take your receipt with you. Worth a shot.

[oldblue1968chevy]

when you say crack the line at the MC, I cracked a line on the ontop of the prop vavle, if I cracked a line going into the MC wouldnt it be the same?..

Fluid is moving freely thru the prop. valve from what I can tell..

[Sammy]

Every week there is a post about MC's. Failure rate even of new ones seem higher than they were in the past.

[cparman]

Probably a bad MC. How about letting them get stuck again, and loosen the bolts that HOLD the MC to the booster. See if that releases the brakes. Might have a clearance issue between the booster and master

[Test Pilot]

Originally Posted by oldblue1968chevy

when you say crack the line at the MC, I cracked a line on the ontop of the prop vavle, if I cracked a line going into the MC wouldnt it be the same?

Correct, get yourself a new MC.

[dwcsr]

The master you should get is the 72 that had power brakes and disc. Some old masters had a residual valve in them that would make brakes hang. This is good for drum but not disc. if the booster rod is out of adjustment it will also gradually hang the front brakes. so make sure when you install the new one that its not putting pressure on the piston.

[oldblue1968chevy]

masters had a residual valve in them that would make brakes hang. This is good for drum but not disc. if the booster rod is out of adjustment it will also gradually hang the front brakes

how would it gradually make them hang?

Should I pull Mc and get new one as a precautionary or play with adj.

[usmcchevy]

Still sounds like it could be one of three thing
1 Hoses swelling and not allowing pressure back to MC.
2 Brake rod too long pushing slightly on MC
3 Bad MC
How to determine:
First I would crawl under the dash and shorten the brake rod about one turn. Then go for a drive if the brakes still hang stop, jump out and crack the line coming out of the MC. If fluid under pressure rushes out and the brakes release, then its the MC if nothing happens then its probably your front hoses. Good luck

[LockDoc]

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Have you tried pulling up hard on the brake pedal to see if it releases the pressure? If the piston isn't coming back far enough to uncover the fluid return hole, pressure will build up in the system.

LockDoc

[cdowns]

did you install a disc brake proportioning valve? drum brakes have a higher residual pressure rate i believe

[oldblue1968chevy]

Im pretty sure ive got the prop. vavle from disc brake truck here is a pic of prop. vavle and my linkeage it just about hits the firewall

[oldblue1968chevy]

Which side of this bracket faces the firewall?

(I had all this stuff off and dunno which way it goes back and its not in lmc)

it is the bracket between booster and rod going to pedel

[dwcsr]

Originally Posted by oldblue1968chevy

masters had a residual valve in them that would make brakes hang. This is good for drum but not disc. if the booster rod is out of adjustment it will also gradually hang the front brakes

how would it gradually make them hang?

Should I pull Mc and get new one as a precautionary or play with adj.

If you used a master for the drum brakes that you did months prior to the disc swap you need to get a disc master. The drum master is different than a disc master,

The recess that the booster rod goes into is shorter on disc and deeper on aa drun master. if the rod is to long it doesn't let the fluid back into the master gradually building pressure in the disc's. Its like alway having your foot on the brake slightly. I would make sure you have a Disc master from a 72 or later truck. but first see if the recess in the master plunger is shallow or deep and see if the rod matches up,, long rod for a deep plunger and a short rod for a shallow plunger. The rod will be either about 2.5" or 3.5" inches when pulled out of the booster. If you hold the master to the booster and it seems like you have to push it that extra 1/16" or so to get it flush with the booster then adjust the rod end so it doesn't have to do that. also look and see if the plunger is stuck slightly in. Thats a sign of a mis adjusted rod and that will hang the brakes.

[dwcsr]

Originally Posted by LockDoc

-
Have you tried pulling up hard on the brake pedal to see if it releases the pressure? If the piston isn't coming back far enough to uncover the fluid return hole, pressure will build up in the system.

LockDoc

exactly right,,, but sometimes the plunger gets stuck in sligthly so pulling up on the pedal doesn't do it.

[oldblue1968chevy]

Im pretty sure I have a disc master clyinder. It doesnt look like the one that came of but roughly same size. I have a pic but wont upload it.

The rod comming out of booster (front side of truck) DOESNT sit flush in the booster it protrudes a little. This correct? It may've been the linkage though. Can someone answer my question about the bracket does it matter which way it goes it is diff. and thats why I wonder.

[dwcsr]

Originally Posted by oldblue1968chevy

Which side of this bracket faces the firewall?

(I had all this stuff off and dunno which way it goes back and its not in lmc)

it is the bracket between booster and rod going to pedel

your thumb would be at the firewall side