Very tight flare nut
 

New rear Mtec discs and fully refurbished rear calipers are back on the 190 at last. Final step is to replace the flexible brake lines. So I pulled out my new flare nut wrench kit and found the 10mm was too small and 11mm was a little too large. I put pressure on the 11mm wrench but felt it was about to round off the flare nut. It's been soaked in 'Ferrosol' for at least a week and cleaned thoroughly. Is it possibly an imperial size nut? I'm thinking that if I tear something I should be prepared for replacing a section of the rigid brake line. All advice very much appreciated.

If you suspect an Imperial size nut then why not try an Imperial size spanner.--:shrug:


PS. Being old I have LOTS of Imperial size spanners. Lol.

Unlikely that it is unified, as 7/16", a standard tube nut size, equals 11.11 mm. I have just had a job & half changing the flexibles on my Rover 45 . Ended up cutting the pipes as the tube nuts wouldn't undo. Fortunately it was the front & it was easy to run new rigid's across inside the engine bay , through the inner wings.
Rears on my Discovery Land Rover , had the same issue and ended fitting new short sections of the rigid as you suggest.

If you're flexibles aren't past it then don't bother changing them is the simple answer. They probably were 11mm many moons ago but if they're as old as the car some of the surface will have flaked off therefore reducing the size. You may be able to get a 10mm to squeeze on if you clean the crusty stuff first, a little heat will help too otherwise prepare to have to change the hard line if you fail. If you've got a decent flarer you may be able to cut a small section off and flare what's there but bare in mind steel isn't the easiest material to flare when you haven't got the proper gear which is made even harder on the car.

With the braided lines you need to be really careful how you route them too, plenty of people have suffered with them rubbing through!!!

Lol. I've got some on order, but I'd like to plan for damaging the union just in case. I've got new flexibles ready since I suspect the old ones are past it, especially as I've had them pinched off for about a month.

Good afternoon Edward.
I seem to keep buying cars that need work on the brakes, so have now met a few seized unions. Your brake union should need an 11mm flare spanner, and if the 11mm feels 'too big' then as rrobson says a combination of rust and possibly previous heavy tightening has started to mangle them.
If you really need to change the flexis then clean the unions, soak in plusgas a few times and let soak. If they won't undo with a proper flare spanner add heat, but this needs a bit of care so you don't cook the flexi by heat transmission through the nut. (edit- just reread that; if you're definitely changing the flexi then just whack the heat on!)
Sometimes they just won't come.The front unions in particular sitting in the wheel arch exposed to all sorts of salt and muck. Plan B is to cut the rigid brake pipe, and knock a tight socket on. Gives more leverage, but I still had to use an Irwin socket for rounded nuts on one of mine. It means a new brake pipe of course- hence the advice to leave the flexi if you can.
Good luck.

Thanks skellum. I had to read the second part twice before the penny dropped.
I've never done any brake work before, but a quote of over £2k was a powerful incentive, so I'm going slowly and taking my time. Your advice is very helpful. I'll post how I get on later...waiting for some bits and bobs now..
Hoping to avoid new rigid brake pipework, but the flexi's have to be changed
so fingers crossed!
If the rigid brakeline has to be cut, how does one best stop all the fluid draining out of that line?

You can stop all the fluid drawing by wedging the brake pedal half way down. Use something between the seat and the brake pedal.

If you need to cut the metal brake pipe, you will need a decent brake flare tool - Sykes pikavant flaremaster is an excellent one. Also use Kunifer brake pipe, not copper. kunifer/cunifer is a cooper alloy-there’s just about no difference in price, but it is stringer and doesn’t work harden like copper.

Pedal needs to be to the floor, but apart from that perfect advice ;)

I normally find the hexagon on unions at this point wasted through corrosion, and take the opportunity to replace what will be usually a poor condition front to rear pipe.

So my method is chop off the pipe flush with the union, then use a single hex socket to unscrew the union from the flexi ;)

If you don't already own a pipe flaring tool, I can recommend this as to my own choice LINK


You will in all likelihood want to get a pair of THESE too ;)

Best of luck

Brian :D

Anybody preparing to do this sort of work, don't skimp on flaring tool, it will pay for itself time after time. I am still using the set I bought 50 years ago and it was nearly a weeks wages at the time.