W124 Brake Line diameter ?
 

Car: 1987 W124 260E with the M103 2.6L engine

Hi, can someone please tell me the correct diameter of the brake lines used in this car? I am also looking to buy the Copper-Nickel (I think these are called cunifer). Can the same diameter Cunifer lines be used in this car?

its 3/16 line - you can either buy the whole roll of cunifer line - but you will need a bubble flaring tool (dont do the half double) and metric bubble nuts to go with it

If you are just replacing one line then you can buy one section of green armor line from autozone, oriellly etc. it comes complete with bubble nuts and flares, you use the bubble flare at the termination end and cut the new line and old line (where its solid) and put a double flare on it and join it with a union.

to bend the line buy a bending pliers from harborfreight and bend the lines into shape.

More on W124 brake lines
 

Thanks for the above info. It was very helpful. To add, the original lines were steel. Mine rusted through this past week after 27 years and 290,000mi. Everything was frozen in place except the end of the line running forward and the ends of the flex lines connecting to the rear calipers. I got out my Fein Multimaster with a steel cutting blade and cut off the flex line joints just above the clips because I wanted to save the clips. I cut the brake lines themselves at the tee, one at a time, marking the ends which connected to the tee, noting their orientation and their connection into the tee. I also had to cut the long line going forward because I could not get it out from under the car without doing that. I bought an 11mm flare nut wrench for this but all it did was round the nuts. What were they thinking when they chose 11mm?

Then came the moment of doubt. Except for the above thread, there is very little out there about this. A couple of things I learned:

The lines are standard European aftermarket stuff, of 3/16in or 4.75mm, with 10x 1.0mm "bubble" ends. Two materials seem to be used. One is steel. The other is copper-nickel-steel (cu-ni-fer for the scientists among you) which is non-rusting, a bit more expensive, and much easier to bend. Definitely the way to go. Lengths I found locally were 20, 30, and 50", which means that the forward line will need to have two unions.

I write this having just purchased all the parts. I wasted a bunch of time checking with the shop from which I bought the car, surfing the internet, and doing a lot of worrying but the solution is a well-supplied local auto parts store. Bless places like Kittrell's & Autozone. They came through with the hard and soft lines at very reasonable prices.

Yup, 4.75 mm same size used by every european car since WWII. Matco makes a decent bubble flare tool, Part No. MBFS241. It takes a few tries to get the technique right, so buy some extra brake line to practice on first. The Matco tool I mentioned is the easiest I've found to use, the cheaper china-made tools take considerably more skill and patience to produce a clean flare with. You also need a small diameter tubing cutter to cleanly cut the brake line to length. The m10x1.0 ends are available in bulk online, I like to replace the originals with stainless.

Put the car as high as possible from the ground, makes it a lot easier to replace the lines.

W124 brake line lengths, materials, bending
 

The brake line lengths for my 1990 W124 turned out to be :
tee to rear left: 17 1/2in.- used 20" line
tee to rear right: 33 1/2in- used 40" line
tee forward: 117 in.- used two 51" lines plus one 20".

I used 2 NiCopp CNE-320 lines, one CN-340, 2 CNE-351s.
In forming the lines, I started with the section going over the differential forward, formed my line to the old steel line and found that I could not get it up and over stuff without a lot of hand forming as I went along. Eventually I just handformed the end I was inserting first and formed the rest of it as I went along. Not as pretty as the old lines but they worked. The excess lengths I formed around and behind stuff which didn't move or got hot, making sure that wherever it might be touching or crossing metal edges I put rubber hoses around them. In other spots, I tie-wrapped to other stuff to keep the new lines from vibrating.

Thanks for the Matco reference. I will follow these lines to make sure there is no vibration against metal objects since these lines are probably a bit more vulnerable than steel. If they begin to fail, I know what to do next.

I appreciate the history about these lines. I have no history working on metal brake lines and this whole area seemed a huge mystery. Reading the comments above got me moving toward a solution. And, it all (including flex lines) cost under $100. Thanks again

You can readily buy the bulk cunifer line from NAPA and all the hardware too. Makes for real easy forming of the lines.

The only other bit of hardware required are called brake line clips, you can use the plastic ones sold at autozone (as the napa catalog is very confusing trying to find those clips) - or if you fancy steel ones then go to a home depot or lowes and buy some hanging clips from the electric section, its a small 1/4 inch steel clip with an eyelet and rubber padding already in it.

I use the OTC bubble flare kit but I also have a GM service part (little flare cubie) to make bubble flares, for the GM tool I have to mount it in a vise. Both make equally usable flares. It takes a bit of practice to make any flare and a dab of silglyde really helps.