[Brakes] brake line union to master cylinder leak

[Kwan4137]

Hi everyone

First time posting on this forum! I'm having issues with the brakes on our 2006 1.6l petrol Berlingo Multispace. At some point the master cylinder has been replaced/tinkered with, and there is some sort of adapter attaching the brake line to the brake master cylinder, that is leaking. Our mechanic thinks there used to be some sort of part inside this adapter that has fallen out meaning that the connection is leaking - and the solution the last mechanic used isn't solid enough. I've attached pictures to help illustrate.

Has anybody come across a problem like this or know how to fix this? 

https://drive.google.com/file/d/1k8loZBK...sp=sharing
https://drive.google.com/file/d/16TnNLYB...sp=sharing
https://drive.google.com/file/d/1QY6xNLH...sp=sharing
https://drive.google.com/file/d/1vgYJG_kdAbTL-CyFueMyrNQAvlN_jfkc/view?usp=sharing 

[oilyrag]

There is a possibility that the fitting is an M12 to M10 brake line adaptor. It could be that the master cylinder fitted was from the incorrect model and had only M10 pipe fittings (if you search the master cylinder for model/period it shows some with m12 drillings which would match your m12 pipe fitting), and a way round this was to put the adaptor in line. There would be nothing inside the adaptor.
However the adators have differing internal machinings on the female part of the fitting.
The pic of the inside of the adaptor would sugesst that the m12 pipe fitting isn't bottoming onto the chamfer and fluid will therefore leak back up the threads. 
Could you post a picture of the M12 fitting/pipe end and also how far it threads into the adaptor. 
Also the male end of your adaptor is fully screwed in, which would suggest that the cone on the end isn't making contact with the matching recesss in the master cylinder. Also that sort of fitting isn't designed to take a copper sealing washer.
The 'fix' might be as simple as getting the correct adaptor (even if the master cylinder isn't year correct and works OK).

[Kwan4137]

There is a possibility that the fitting is an M12 to M10 brake line adaptor. It could be that the master cylinder fitted was from the incorrect model and had only M10 pipe fittings (if you search the master cylinder for model/period it shows some with m12 drillings which would match your m12 pipe fitting), and a way round this was to put the adaptor in line. There would be nothing inside the adaptor.
However the adators have differing internal machinings on the female part of the fitting.
The pic of the inside of the adaptor would sugesst that the m12 pipe fitting isn't bottoming onto the chamfer and fluid will therefore leak back up the threads. 
Could you post a picture of the M12 fitting/pipe end and also how far it threads into the adaptor. 
Also the male end of your adaptor is fully screwed in, which would suggest that the cone on the end isn't making contact with the matching recesss in the master cylinder.  Also that sort of fitting isn't designed to take a copper sealing washer.
The 'fix' might be as simple as getting the correct adaptor (even if the master cylinder isn't year correct and works OK).

Hi thanks so much for the detailed reply. Yes the m12 pipe fitting isn't bottoming into the chamber - I've attached a picture showing how far it threads in (first pic). Also I've attached two pictures of the pipe end. Does this look like a shorter adaptor (something perhaps like this https://www.carbuilder.com/uk/brass-unio...2x1-female might be a suitable 'fix'? 

Thanks again for looking at this!

[oilyrag]

If you look closely at the thread on the m12 pipe you'll see that it is badly damaged - either by cross-threading it into the adaptor or the adapator having the incorrect thread. It will be difficult to recover that fitting and it certainly won't want to thread into brass. You may be able to use a triangular Swiss file to very carefully re-cut the thread, starting at the good part and working outwards, having blocked off the bore of the pipe with something like a pipe-cleaner.  It only went part of the way into the fitting, which might suggest wrong fitting thread - any hydraulic thread, if matching, can be screwed in fully with just fingers.
I'm unsure as to whether the fitting you have shown is the correct type - it says Concave - but whether that matches what you have, at either end of the fitting, isn't that easy to confirm. Also the 'male' end needs to be long enough to bottom out in the master cylinder thread in order to make contact with the shaped inboard end and seal.
The threads on either end of the adaptor don't play a part in sealing, it's the shaped ends that do that job.

[oilyrag]

Bad thread.