My brother owns a 2000 XJ 4.0 Auto ~160k

A couple of days ago his wife was backing out of a parking spot and someone pulled behind her and she hit the brakes hard. The truck stopped, but the brakes went soft. She perhaps foolishly drove it home. Now it has very little brakes and the pedal goes all of the way to the floor.

I looked it over and all of the lines above the left rear wheel are covered with brake fluid. It does not look like the master cylinder or wheel cylinders failed. However it does look like the metal brake line that runs from the front of the Jeep to the rear - right before it turns into rubber and splits to feed both rear wheels is corroded and failed.

Several questions
(1) how common is a failure like this, should I be proactive and replace old lines... this could have been bad at highway speeds
(2) I thought there was some kind of a system that separated front and rear brake systems to that if one failed the other would still work. Am I looking at multiple issues with the brake system or is the soft pedal and minimal braking common when this happens?
(3) Someone told me that this happens when braking hard in reverse. I don't see how the direction of travel could affect this at all, any relevancy to this?
(4) I know after I replace the lines I need to use new fluid and bleed the brakes, anything else I should watch for or be aware of? I have replaced pads, rotors and even wheel cylinders before but never brake lines.

Keith

 

1) well it just depends on where you live i guess , i would do a yearly inspection

2) they are separate but they work together so an open line would have that affect.

3) your right makes no seance.

4) i think you got it ,

 

thanks, I appreciate the response.

Keith