hi, after having done two of these, both resulting in replacing not only the rubber part but also the copper pipe to the distribution stock as the joint was not to open and the pipe was about 10$ only. both on left side only as somehow the right side joint was to open without any difficulties. mine were 2x 840-94s.
br tapsa

Only one maker of flair nut wrenches really work, SnapOn tools. Even Craftsman at Sears are too weak to do the job. The 850 brake lines are 11mm IIRC, but just take a regular wrench and check it out for size. The caliper end is usually easier than the brake line end, where you need 2 wrenches.

If I were you, I would do both front brakes lines at the same time. And flush the fluid with new DOT 4.

Klaus
--
Proud owner of a 220S. If I had more room, I would have more Volvos.

You will definitely need a set of flare nut or 'line' wrenches. They look like a normal box wrench with a slit out of the end of the box so you can slip it over the brake line like this set of Westward wrenches (first decent picture I found):


Get six-point wrenches rather than twelve-point wrenches.


As it seems you are as under-educated about this as I was not long ago I'll spell out my findings in this area for you and the rest of the folks on the board who have run into this problem.

The easiest way to put in a new piece of flex line is to also put in a section of pre-made rigid line from the auto parts store.

Start out by putting a piece of board or something in place to hold your brake pedal down. This will keep the fluid from leaking out of the line while you're working on it.

I only use my flare nut wrenches for installation now. I've pretty much given up on trying to get this stuff apart without ruining it. The last couple of times I had to replace a flex hose, I really only gave the flare nut one chance to come the easy way - the very next step was the angle grinder with a cutting wheel.

I make one cut on either side of the little bracket that the brake line is threaded through (the bracket that holds the upstream side of the flex-hose to the body). Sometimes I end up having to drill out the bracket somehow so I can reuse it, but things usually start coming apart pretty easy once you start cutting.
Here is a pic of the type of bracket I'm talking about:


Be careful when cutting not to set the fluid on fire - only cut a little at a time and take some breaks to let things cool off a little as you go. Wear eye protection (A full face shield would be preferred) and a mask and gloves and a long shirt.

To put everything back together, you'll need a length of pre-made brake line from the auto parts store. These come all done up with a flare and flare nut on each end. I always buy the longest length they have, since the 8" length is usually only ~$1 less than the 6' length and you're going to cut it anyway... (more to come)

There are two main types of flares/flare nuts, and they are commonly distinguished as 'bubble' and 'double'/'inverted'. The double/inverted flare is the traditional style for american cars (as far as I can tell) and the bubble flare seems quite common on european cars like the Volvo.
Here's a pic that shows the difference:


Since all your hardware expects bubble flares, you'll need to buy the correct sized line (3/16 I think) with the correct sized metric bubble flare on the end. You can easily find the correct flare size by bringing your new flex hose along with you and trying it on the various flares until you find the one that fits.

In addition to the pre-made line, you'll want to pick up a 'double'/'inverted' flare kit (the usual type of flare kit - the ones at Harbour Freight or Princess Auto are fine for home use), and the hardware for making a coupling - two double flare nuts and a double flare coupler, as well as a tubing bender tool.
Flare kit:

Flare nut:

Coupler:

Tubing Bender:


What you're trying to do it put a new double/inverted flare on the end of the line still on the car, and couple that to a new double/inverted flare you put into the pre-made line you just bought, so that your flex line can fit onto the nice bubble flare on the other end of the pre-made line.

Of course if you can buy a bubble flare kit and know how to make bubble flares you can skip all this, but it seems like the inverted flares are an easier/cheaper DIY.

So your final setup will look like this:

legend:

IF< inverted flare

>FI inverted flare (facing opposite direction)

___ inverted flare coupler

BF< bubble flare

>FB bubble flare (facing opposite direction)

*** bubble flare coupler (on flex hose and caliper)

--- rigid line

=== flex hose

+++ bracket holding hose to body





         _____       *****          **********

--------IF< >FI-----BF< >FB========BF< caliper

                    +++++++          

The fitting is likely to be very tight. Use a brakeline or flarenut wrench - measure it to be sure of exact size. You may need to heat the flare nut with a torch to make it possible to remove.