If you’re replacing the brake hoses on an E34, or planning a task that involves removal of the front hub, you need to undo the fastener that attaches the metal brake line from the body to the rubber brake hose that leads to the hub.
Two open-ended wrenches worked well for me, for this task. On the brake hose side, the fastener is a 14 mm sort-of-nut attached to the end of the hose. On the brake line side, the fastener is a 11 mm nut that fits over the end of the brake line.
If I were to strip either fastener, the stakes go up, so I know that I basically have one chance to do this right. I get (and keep) the wrenches onto the fasteners squarely, and if I feel they’re slipping, I stop. If they’re too tight to undo, I douse them in penetrating oil, and I wait.
A good trick for me is to angle the two wrenches in such a way that they both barely fit into the palm of my hand, and when I squeeze my hand shut, it forces the wrenches to be more parallel, and in the process, the fasteners gets loosened.
Once the 11 mm nut was loose, I ignored the 14 mm aspect and I focused on loosening the 11 mm nut more and more. Pretty soon, brake fluid (which I recall to be a blend of oil and acide) starts to seep through. If I hold my arm at the right angle, I can manage to have the brake fluid run down my hand, down my wrist and along my forearm all the way to my elbow. (I don’t recommend this). It’s a good idea to be prepared with a vessel in which to catch the dripping brake fluid. Re-using the same fluid tends to not be a great idea, I’m told.
When you eventually re-tighten the fasteners, make sure you don’t overdo it and strip them. Also, you’re almost guaranteed to have to bleed the brakes.
This write-up doesn’t cover detaching the hose from the hub, because I haven’t as yet done that on an E34.