I Had some over the weekend – the offside front piston had started sticking in the week so I replaced the seals and cleaned the surface corrosion off the piston.  I had just finished bleeding the brakes when I stamped on the pedal to test for firmness and the rear line split near the ‘U’ bends before the steel pipe joins the flexible pipe.  Luckily it happened on the drive and not down a hill.  Thinking back I remember an advisory on the last MOT but it looks like they’ve corroded much quicker than expected.  So – if your E46 rear brake lines are corroded I have put together a quick guide.  I checked the opposite side and sure enough it was also starting to go – so if one side has gone, the other won’t be far off – replace both.

Options for replacement:

  1. The lines can be replaced by new ones from BMW.  Both join under the drivers footwell somewhere.
  2. Make your own lines from copper / copper nickel and join onto the original steel pipes with unions.

I went for option 2 – mainly because I could get all the parts and BMW didn’t have stock on the day I needed them.  I’m not sure what other floor panels need to be removed to gain access to the unions as I put my joins just before the pipes turn up to go above the fuel tank.

Major parts required:

  • 13mm ratchet spanner – I didn’t have one and would strongly advise buying one before you start if you don’t have one.  I guarantee this will save you a lot of time!
  • 3/16 brake pipe – I used copper nickel because that’s all the parts store had in.  Normal copper will be fine and easier to flare and bend
  • M10x1.0mm male ends (8 off)
  • M10x1.0mm unions (3 off)
  • Brake flaring tool – one suitable for mild steel to flare the OEM pipes
  • Red rubber grease for the flaring tool which can create single DIN type flare for 3/16 pipe
  • Pipe cutter
  • 11mm spanner for the brake pipe unions
  • 15mm/17mm sockets / spanners

Undo the bolts for the fuel filter panel and the heat shield around the exhaust near the fuel tank

Remove the two bolts from the fuel tank straps – note I had very little fuel in the tank.

Undo the centre bolt which holds the fuel tank but do not fully remove it.

Take the rear seat out and undo the 10mm bolts on the inspection cover on the near side.

Follow the brake lines and undo the clips – they have a 13mm plastic bolt.  Use a 6 sided socket set (don’t be tempted by the 6mm hex drives) to avoid cracking.  I only have undid them to leave the clip in place and it leaves enough room to spin the metal cover 90 degrees to pull the pipes out.  Leaving the clips in place makes putting them back much easier, particularly the clip above the fuel tank (you’ll know it when you find it!).

I made up the pipes to follow the exact same route as the originals – this is easy to do when you have cut the originals from the car.  I staggered the cuts so that the unions would not fowl on each other.  I also put in a union where BMW placed one for the offside pipe which traverses the car near the flexi joint for the nearside.  You could probably do it in one piece if you fancied a challenge.

Do all the joints up and re-bleed, doing the rears (longest runs) first.  Ensure the pedal has good pressure and does not sink, check for leaks then road test – perform some emergency stops where it is safe to do so to build up the burst pressure, then check for leaks again.

In total I did this over two days, only working about half the day on each one around family commitments.  It also took an hour or so to figure the brake flaring tool and practice making some decent flares.  The tool I had access to was a Sykes Pickavant vice mounted type – fine to make the new ends off the car, but more challenging to make the ends on the car – with enough clips undone you can bend the pipe slightly out to the side of the car.  Sorry, I didn’t take any pictures of this work, I was too busy trying to complete it under time pressures!

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