Brakes have worked fine for last five years. All new everything.

couple weeks ago I developed a leak that I think came from back of MC wear it touches the booster.

the MC was lifetime warrenty from Autozone and not rebuilt but new. Took it back and got identical model.

this time it came with different instructions. Last time it came with hoses that went back into the MC. I put it on the car with those hoses and pumped the brake pedal very very slightly till it got all the air out of the hoses and then attached the brake lines, put my pressure Bleeder on top, and purged all air. Brakes were great. THIS TIME the MC came with block off plugs and said to bench bleed and make sure no bubbles. Well I pumped and pumped and pumped with a blunt wooden stick and never was able to get all the bubbles out. Say there for half an hour. Put it on my car and put the pressure bleeder on and pumped it up to 10Lbs pressure. Bled the system. Got all air out.

went for a ride and had GREAT pedal. Till about a quarter mile and then lost all pressure. white smoke pouring out under the car. I had brake fluid all over the header under the MC where the Portioning valve is. I ordered a new portioning valve, made very sure the lines were properly seated and tight, even though I suspected it was fine, installed that, gravity bled the system, then pumped up the pressure bleeder again. Got any remaining air out, topped off the MC and went for another ride. Great pressure. Great pedal. Till I hit the brakes hard maybe the 10th time. Lost all pressure. Started a Fire on the heat wrap around headers this time. Thankfully I was home and the hose was there and put it out. No damage. Washed the headers off with lots of water and started car and smoke went away.

pumped up again, bleed out air, great stopping, till fourth hard stop. fluid all over the headers again.

so. Thoughts? Why do I get 10Lbs of pressure and no leaks but then go for a ride and lose my fluid and no peddle? Did I have a faulty MC an and that’s why I never was able to bench Bleed the bubbles out?

 

Can you tell where the fluid is coming from? That is where the fault is.

 

The very first thing to consider is to indicate what make, model & year vehicle for your issue(s). You'll garner far more pertinent/applicable assistance.

 

That’s weird. It used to be in my profile signature in side.

1970 Olds 442 convertible.

 

X2. You need to have someone pump the brakes hard while you are watching under the hood to see where the leak is.

 

Brake pressure is closer to 900-1000 lbs if not more. Your 10 lbs is ok for bleeding but is nowhere near normal operating pressure.

Just want to add that a good friend/customer of mine that does restorations Had some problems about a year ago with brake line fittings that he was buying from one of the local parts stores. I think he tried several brands and found that they were all made wrong and would not seal properly. He got on E-bay and found someone with some old stock fittings from 30 years ago and that solved all of his issues.

 

Here's a master cylinder bleeding kit:

https://www.oreillyauto.com/detail/c...kit/mtm0/14151
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Rust holes in the metal brake lines don't magically fix themselves, so I think we can rule that out. From your description, you apparently don't have a leak from the M/C. Is this a factory disc brake setup for 1970 with the metering valve at the M/C and a distro block on the frame, or is this a conversion with a Chinesium brass combo valve?

 

I'd recommend always bench bleeding a MC with hoses. You can do that in the car like you did, too, but it's better with the MC level.
Personally I don't like the "plug and pump" MC bleeding method. PITA and seems to be more touchy.

I'll place a bet (with very small monetary value) that your replacement MC has already failed. I ran the Dodge style MC for a while and I would buy them in batches of three because there would always be two that were trash (scratched bore, bad piston install, twisted seals).

 

How can a failed M/C spray brake fluid then not?

 

 

¯\_(ツ)_/¯
How can anything spray brake fluid, then suddenly not?? It's a wacky failure whatever it is, and my first go-to is to question the newest replacement part especially if I don't have a very good reason to trust that new part.

 

Except that it did it before he replaced the M/C. My money is on the combo valve, probably a bad o-ring seal.

 

Replaced the MC again. This time used the Bleed with hoses methods. Went better. Was done in no time.

pressured it all up again and found the leak. It is the Rear brake hard line connection where it attached to the valve.I had to drop the header to get a line wrench on it backed it off and reseated and tightened it more till it wouldn’t give. Pressured up again and it started leaking again! backed of off again and made sure the hard line was square and tightened the nut and pressured up and still leaking.

This hard line was brand new 1000 miles ago from OPGI. I compared the new valve to the old one that I thought failed and the connection is same.

based on what you see in this photo does it look like the hard line was not Flared correctly?

 

Well, it's impossible to tell without a photo of the flare on the hard line, but that fitting on the combo valve is trash.

Consider next time don't be so ready to throw money away on replacing new parts that can't be the cause of the problem.

 

Post a picture of the hard line flare, if it is bad it will damage the surface to which it mates. My guess is that it is bad now even if it wasn't from being connected to the surface in the pictures supplied.

 

The flare in the steel line likely wasn't going to be damaged by the soft brass combo valve fitting. More likely is that the flare on the hardline caused those gouges.

 

Agree, which means it is likely they will both need to be replaced at the same time.