I have the unfortunate problem of an almost rounded passenger side flare nut on my brake system and the joint is still not apart. (where flex connects to hard)

Option 1> Use special vice grip and 14mm flare wrench to get existing apart.

Option 2> Cut and remove existing line and install new full length steel line with pre-installed bubble flares.

Option 3> Cut and remove existing line and install new full length cupronickel line with or without pre-installed bubble flares.

Option 4> Cut existing line where it comes through into wheel well and install a new flare nut and a bubble flare union.

Option 5> Run flex line all way from MC to caliper.

Comments on Options 1-4 and 5:
- Option 1 may work and is my first choice. But nut may get mangled.
- Option 2 will be hard to achieve because of multiple bends needed and tight space to thread line through.
- Option 3 requires bubble flares to be made in place. I would need to buy a flaring tool and practice a little first! But if I can find a shop to put the flares on, perhaps I could then bend the cupronickel by hand as I go?
- Option 4 requires bubble flares to be made in place but at least access is easy.
- Finally option 5. I read on some other forums, that some BMW and other owners have run flex lines all way from MC to calipers on all 4 wheels. And some of these guys are racing. They say it works well! Anyone heard of that on a 123/126? And then where do I source the lines? Certainly would be easier to feed the lines across the back of engine!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I assume your referring to the Vise-Grip 4LW model with the notch in the fixed jaw. It is a great brake line tool.

The trick to loosening brake hoses is this: You want to hold the flare fitting on the hard line immobile and apply all the turning torque to the hose fitting. Keep in mind that the tightened hose fitting clamps the flare in the line to the hard-line fitting. That makes the hard line and the flare fitting act like it's one piece. Apply turning torque to the flare fitting and you run the risk of twisting the hard line.

I often cut the hose off so I can fit a deep 6-point socket on the hose fitting. Then I use a 3/8-inch drive breaker bar. You can really crank on the hose fitting that way.

Wow Graham - I hope my next comment is taken as constructive criticism - but I think you are really over thinking this.

I know it is easier to give out advice when you are not emotionally involved with actually doing the job - I know some jobs are a bit daunting - but you have to crack on and start to do something other than over analysing it!

Give it a go. You've got a spare car if this one ends up with out any front brakes for a while.

My choice would be to try the fancy pliers if you can get them - that has the potential to be the easiest fix.

If that doesn't work I'd set to pulling the hard line out of the car - then I'd replace it with what ever can be made locally for a reasonable amount of dosh.

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Flexible lines from the master cylinder to the caliper is in my opinion a seriously expensive solution - they would have to be metal coated super duper high spec to stop any bulging during use - I am surprised that "racing people" consider that to be a good fix - I'd expect it to make the brakes feel really unresponsive; hard lines tend to flex less than the flexible ones...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

None of the Lines except one are long.


If the old brake Hose is still working just leave it there for a few Weeks while you get some better equipment. The only extra work is another brake Bleeding Job when you are ready to change it out for the new Hose.

This is on a non-Mercedes but one time there was no room to mess with the Hose/tube Junction and I was able to remove the tube at the Junction Box and remove the Hose at the Brake Caliper and took that whole thing over to My Vice and with one end of it mounted in the Vice and a lot of room to work in was able to take it apart.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

I hope you meant lines!

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

It is the weekend, and the vice grip tool will only be here tomorrow. So I have time to overanalyze, because that tool IS my first option. But even if I am able to seperate that joint, the brass flare may get further damaged.

I have looked at that line quite a bit. A prebent line won't work - too complex a shape to fed through and clamp. So I need something flexible or that can be bent by hand. That's how I got to either braided flex or cupronickel.

Buying a flare tool, cutting off existing damaged end and installing a union and short extension may be easiest option. But I would need an inexpensive flare tool capable of flaring the existing steel line.


I am on my tablet and don't have the link, but I think a 60" DOT approved flex line costs about $35. Just don't know if they offer the end fittings needed. 60" would probably be enough to get from mc to passenger flex line bracket. It would be easy to install.

70" thermoplastic flex lines http://www.amazon.com/Thermoplastic-Flexible-Hydraulic-Brake-37204-70/dp/B0079VH2CM

Stopflex braided s/s http://www.classictube.com/products/stopflex-ss-braided-hose

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Ahh I didn't realise the fancy pliers are on their way and you had time to think about all the what ifs...

...I doubt very much the end of the line will be damaged.

If you were to go for a flexible pipe all the way from the master cylinder why wouldn't you plumb it straight to the caliper?

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I prefer short Lies

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84 300D, 82 Volvo 244Gl Diesel

Its the flare nut that is already damaged and may get worse once I use the vice grip.

It would seem to make sense to run a flexible line all the way to the caliper, but I read that this type of line usually fails at swage end due to flexing back and forth as wheels turn. I have new rubber flex lines as far as the bracket anyway. In future, it will be easier to just change them rather than the whole line.

It seems that some local parts stores may offer free rental of a quality flaring tool. Depending on size of the tool and access, it might be possible to just add a short piece of steel tubing with a new flare nut and union. Will check that out tomorrow.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The problem side already has the flex line cut. Other side has been rebuilt, so I guess I could drive with one front brake

Taking whole assembly out would be nice. Might be possible on front driver side, but definitely not on front passenger side! And that is no LIE

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

If the flare nut is already damaged what are you worried about? Put a vise grip on it! If the rest of the line is sound, then use the vise grip to tighten the flare nut to put it back together. If the line is rusty, replace it now! Cut the old line in pieces if it makes it easier to remove, then you can measure the length of the pieces to make your new line.

I highly recommend you use Cunifer line, not only is it easier to bend, it is much easier to flare compared to steel line.

Flaring tools are not created equal. Some work better than others.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The flare nut is not so badly damaged that I want to ruin it with ordinary vice grips. If I can get it loose with the special Vise-Grip 4LW, I may be able to file hex back to shape.

Provided that will allow me to properly seat the nut into the new flex hose fitting, that will be it. But if I can't get nut off without totally wrecking it, then I will have to go with one of the other options. Most likely the Cunifer one.

One thing that surprises me, is that the bubble ends on the original brake lines can be re-used when installing new flex lines. You would think that the end would partly deform when tightened (especially if soft like Cunifer) This is what on-line source says:

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

This one is a bit long but gives a good overview of the flaring process with some good tips on making cheap flaring tools work.

https://www.youtube.com/watch?v=iUDyEu_NYK8

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks, will keep that for future reference. The mini vicegrip tool got the job done!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I've got all three of the Vise-Grip LW pliers, but the 4LW -- the smallest -- is far and away the most useful.