Brake line won't stop leaking at the nut"

[brent]

If you recognize my name you know I've been haltingly working on the brakes of my 66 Monaco. Today's (and yesterday's) mystery is the brake line running from the "T" at the differential to the driver side rear passenger wheel cylinder. All the components in the brake are new. The original line was so rusted it had to be broken to pull the wheel cylinder. I tired creating my own flare on a new line (multiple times yesterday) and it leaked from within the flare nut outward at the wheel cylinder. Today I replaced the line with another that had only manufactured flares and nuts. The same results. The leak comes from within the nut so clearly the line is not seating properly against the cylinder (though it feels like a good seating as I tighten the flare nut down. I'm out of bullets and nearly out of patience with this seemingly simple repair.
Is there anything I can paint on the interior of line or between the line and flare nut to stop the leak? Can a wheel cylinder be so badly cast as to cause a leak? (it looks fine inside) Must I purchase a line specific to the model, it's 3/16 diameter line with 3/8th flare nut/24 threads per inch.

 

[Rapidtrans777]

It's possible it is a bad casting. Its either the line or the cylinder and you've replaced the line. As cheap as wheel cylinders are I would replace it. Do not try to rig it, brakes are not something to cut corners on.

 

[Mr C]

As mentioned, this is a symptom of a bad flare, or contamination that won't let the flare mesh and seal. either the line or the casting is off or it isn't clean.

 

[saforwardlook]

Are your lines made of stainless steel or mild steel? I have heard that stainless steel is notorious for being a problem in this regard, but never used them myself because of the rumor, and because my cars will not see wet weather.

 

[brent]

Cleanest cylinder is the new one that leaks at the nut. It appears to be flatter inside the flare nut bore.
I caused that via tightening or the flare on the line is a different type than the original as noted in the other two dirty cylinders. Discerning eyes?

 

[Davea Lux]

I would pull the wheel cylinder and check the seat for the line flare. A lot of the Car Quest and Auto Zone cylinders are made in China and their stuff has quality control issues. I have run across several that have had bad bleeder screws or bad seats for the bleeder screw. If it is defective, Auto Zone or Car Quest should replace it with one of similar quality. Also check the flare for the line where it should contact the raised portion of the seat. As noted above, the stainless lines are considerably harder than the OEM steel ones and that can cause problems getting a good seat. Also note that brake tubing uses double flare fittings, single flared steel gas line tubing will not work. Look closely at the imprint made on your wheel cylinder where the line contacted the seat, there should be a ring all the way around the seat, in which case it should not leak. If there is a gap in the ring, that is where your leak is, you will need to replace either the line or the cylinder. There are numerous online instructions on how to make a double flare brake line. Try the NAPA know how site.

Dave

 

[68PK21 440.6bbl]

The middle wheel cylinder in your pictures is junk, bottom pic one ain't much better.

Middle one enlarged

Are you using these type of wrenches to tighten the line?

 

[brent]

Middle and bottom photos are the pulled cylinders, top is the new purchase. I've done some more investigating around town. Autozone had two more of the same cylinders and they look exactly like my top photo so I've done no damage. I also pulled the brake apart and bolted the cylinder to the line by itself. So far, no fluid leaks at the flare nut-strongly suggesting it's the angle of my dangle causing the problem. I'll leave it on in this fashion and pump the brakes a few more times to see if that's truly the issue. I tend to always feel I'm the weak link in the process and it may be true again.

I really do appreciate the various suggestions and perspectives.

 

[stubs300]

So far, no fluid leaks at the flare nut-strongly suggesting it's the angle of my dangle causing the problem. I tend to always feel I'm the weak link in the process and it may be true again.

Sometimes your afraid of over-torqueing it and breaking something, I know the feeling! Good Luck

 

[brent]

Possibly a helpful hint for others. Hold the brake line back against the flare nut as you tighten it in. Seems to have set and no drips (so far).

 

[LocuMob]

I was going to ask if you just put the nut on and tightened it up. I always hold the line down while getting the nut snug, that way you know it should be seated and won't leak.

 

[CBODY67]

Some times, "simple repairs" can become otherwise, especially on older vehicles. No matter what.

CBODY67

 

[Fury Pursuit]

Brent, you need to double flare the new line, not just a single flare.

 

[cantflip]

The middle wheel cylinder in your pictures is junk, bottom pic one ain't much better.

Are you using these type of wrenches to tighten the line?

IMO... you might eyeball a damaged seat... but the ones that look good can fool you too.

Middle and bottom photos are the pulled cylinders, top is the new purchase. I've done some more investigating around town. Autozone had two more of the same cylinders and they look exactly like my top photo so I've done no damage. I also pulled the brake apart and bolted the cylinder to the line by itself. So far, no fluid leaks at the flare nut-strongly suggesting it's the angle of my dangle causing the problem. I'll leave it on in this fashion and pump the brakes a few more times to see if that's truly the issue. I tend to always feel I'm the weak link in the process and it may be true again.

I really do appreciate the various suggestions and perspectives.

There are no products that should ever be used to seal a brake fitting. The double flare is for strength, and prevents the flare from getting blown off during extreme braking (panic stops)... so it is very important that it's done correctly. Poor flares or any defect at the seat (including ones you don't see so easily, like a bad angle) will cause problems eventually.

It is good that you are being careful, and critical of your own work. The threads on these kind of fittings are pipe threads and designed for an interference fit... it makes them a little more difficult to work with, but not usually too bad. The advice to wiggle and hold the line is good, it does help assure that you seat the flare if the line has any bend to it. Try to be careful the line is straight at the flare, when you bend them yourself it is easy to put the slightest curve under the nut and make your life more difficult.

More thoughts or hints for doing this job... try your best to duplicate the factory routing and mounting of the lines. They were originally secured enough to prevent vibration damage and routed so that road debris was less likely to damage them. When making your own flares, the quality of your results will greatly improve if you spend a little time making certain you start the flare with a squarely cut and deburred line.

 

[rags]

and use cu/ni brake line. super easy to work with, lasts forever and it's very forgiving. just secure it well.