How to Flare?
 

Greetings,
I cheated when replacing my steel brake lines by doing it in 2 parts, split right in front of the rear wheel. Now I cant get the flare union to work. Using the Harbor Freight double flaring tool, I double flare it, then screw it together. If side A seals, the B side leaks. If the B side seals, A leaks. What am I doing wrong?

Could the lines be too short to seat in both sides of the union?

I dont think so; I havent tightened down the clamps yet, so there'd be enough play for them to get together. Also, both sides of the union show marks on the inside from contact when taken apart. I think I'm just doing something wrong on the actual flaring.

Mercedes does not use the standard double flare. They have a metric spec bulb type of flare that is not compatible with the normal doulbe flare. If you go to most parts stores they have brake lines with the fitting already made. They have US, British and european metric, maybe more.
Make sure to take an old line with you to visually match to type of flare.

I agree with the last post. Harbor Freight is not exactly known for fine quality products. Unless the lines are very long and including a cheap tubing bender (if needed), you may be able to but the fitted lines for under $20. Make sure you secure the lines!

Mercedes brake lines
 

Yeah, Mercedes uses European bubble brake lines incompatible with US double flare tools. They are hard to find. Autozone stocked only an adapter, Jap flare on one end, Germany bubble on the other. Car quest had nothing. Advance Auto Parts had everything including the unions. Measure your old line along the bends with a tape measure, get something a little bit longer. Get a line a little longer than you need, or a couple, and a union or two. If you are a little bit long you can bend the extra into a 3" circle just above the connection to the rubber hose. A tip the Advance Auto lines had red ends, and something that looks like a little ball on the end. I use a Lisle bender, that Car Quest sells.

Greetings, and thank you all for your input. The funny thing is, where the new line connects to the OEM parts (master cylinder, etc) my flares are fine. Its the brand new connection that I made w/o mercedes flares/union that are giving me the problem. Maybe I need to consult the package they came in to find out just what type of flare they are?