Download Mercedes W123 Fuel Injector Hard Line Replacement – Step 1 Begin by marking the hard lines. Each one goes in only one location, it will make it easier to re-install the lines or to install your new lines if you mark where each shaped line goes on the injection pump/injectors. Step 2 Then begin removing the clamps that hold adjacent hard lines together. You’ll use a 8mm socket on top of the bolt that holds the clamps together, and a 8mm box end wrench on the bottom nut that the bolt goes in to. Go slowly with this and be careful to not drop the nuts or clamp pieces as they can fall behind the injection pump. It’s not impossible to get them out, but it can be difficult. The second picture shows the hard lines with all of the clamps removed. Be sure to re-install all of the clamps on the lines; they help prevent the lines from vibrating excessively. The vibration is what tends to cause them to crack! Step 3 Now, use a 17mm wrench loosen the rear-most nuts on the hard lines at the injection pump.