I have an 87 740 that developed a leak in the aluminum high pressure line that runs along the frame on the passenger side. It seems to have corroded from dirt etc that accumulated around the rubber hold down straps. I first checked the FAQs here for a solution, but while it cites this as a common leak problem, it does not provide a solution.

I thought about cutting out the corrosion and inserting a union using a double flare. I discussed this with an home AC repair guy and he suggested trying JB Weld epoxy to seal the leak. Unfortunately, this did not work for me, so I went back to plan A. In the process of trying to get the union in there the tubing cracked where the second strap had weakened the line. So here is my new plan. I am going to get some three-eighths copper line and replace the section of three eighths inch aluminum line using a union for a double flare connection. My primary concern is whether or not a double flare union joint will hold up under the pressure, which I would expect it would as I have used this connection on brake lines without a problem. I also wonder about the compatability of the brass unions with the aluminum tubing.

I had considered replacing the whole preformedline, but I ran into two problems. One is that I haven't found it available for sale. The other is that it looks like it would probably be impossible to fit it in place without removing just about everything in the engine compartment.

FYI my system had been converted to R-134A several years ago.