I need to replace the brake pipe that runs along the underside of the zj to supply the rear brakes as it has a leak. The existing pipe is steel and has a coiled winding around it. I'm in the UK and can not find this part locally. My Haynes manual says not to use copper pipe. Anyone know the reason as I was going to buy a flaring tool and use copper which is commonly used here. If anyone is in the UK and has a solution I would be grateful. Also, does anyone know the fitting sizes ?
You will not find an off-the-shelf replacement. Copper is not strong enough to withstand the pressure. You need steel brake line. I prefer the type with polymer coating. You should be able to source from auto parts store in various lengths and then bend them to fit. Note that a single flare is not sufficient. You need a double flare. I just replaced all the brake lines on mine and they used 3/8" fittings.
NAPA sells a coil of copper brake line. I used it since in upstate ny I would be redoing the steel lines every 2-3 years with all the salt. I've had the copper in for 2 years, approx 40K miles without a single problem. I would imagine as long as you are using copper alloys designed for brake line use, you would be fine. Either way, make sure to get a quality flare tool and bending tool. It will make your life so much easier.
The copper line you would see for brake lines is or should be an alloy (zinc/nickle probably). It is DOT approved and totally legal for use anywhere. There are many OEM's using this kind of line. Pure copper line is a big no-no, illegal and dumb to use, plus its going to be hard to come up with fittings/adapters and getting flares to take and seal.