Replacing Brake Line and Bleeding System

[Cunning Plan]

Our BMW E39 failed its MOT on a few items, one of which was the front-to-rear brake line/pipe.

If I disconnect the affected pipe to install a new one, will I need to bleed the whole system again?

My understanding is that the 4 brake pipes, which go to each individual wheel are separate at the master cylinder, so letting air in one, should not affect the rest?

I am just working out how much time I need to allocate to it..

[Jamieg285]

I don't know the technical answer, but if it was me, I'd do them all.

[Andy]

An E39 I guess has 4 wheel ABS Module, so you're replacing the line from there?

You should be ok, if you make sure the module is always full of fluid and that removing the pipe doesn't allow the reservoir to run below the low mark.  

Again though, for peace of mind, might as well bleed them all, besides, if a line is corroded, could probably do with flushing out all the lines and putting new fluid through.

[Cunning Plan]

Quoting: Andy

An E39 I guess has 4 wheel ABS Module, so you're replacing the line from there?

Yes, I *think* it has, but I am not replacing the line from the module, there is a connection further down where the pipes exit the bottom of the engine bay and go along the chassis to the rear, so I am replacing from that connection to the next connection nearer the rear wheels.

Quoting: Jamieg285

I don't know the technical answer, but if it was me, I'd do them all.

Quoting: Andy

Again though, for peace of mind, might as well bleed them all, besides, if a line is corroded, could probably do with flushing out all the lines and putting new fluid through.

I think you guys are right, I had given the car a full brake fluid change a few months ago, so it is just annoying to do it again.