Brake pipe flare nut size ?

[iangsi]

Does anyone know the correct spanner size I need to fit the 4 flare nuts that hold the solid brake pipes into the master cylinder as out of all the spanners I possess metric or imperial none fit properly 10mm is to sloppy & 9mm does not fit ?
There's a set Machine Mart have but the sizes are 8,10,11 & 12mm.
& another cheaper combination set that goes 10\12, 13\14 15\17mm.

[vexorg]

They are usually 9 or 11. Are you sure it's not just rusted or dirty

[Robsey]

Yep - 9 rings a bell for me.

You could try 3/8 (9.5mm), but I think Vexorg may well be correct when he says you probably have surface corrosion causing a slight over-size roughness on the nut faces.

[vexorg]

You can try chap an open 9mm spanner on the flats to see if that cleans it.

[Robsey]

Yes I have done this on the van...
Got a 9 mm open ended spanner, and wiggled it side to side whilst pushing it onto the flats of the nut.

It sort-of walks the jaws of the spanner onto the nut.
Gives a nice snug fit.

[iangsi]

I managed to tap on an imperial spanner but when I put pressure on it to try & undo the nut it started to slip off & deform the nut, so admitted defeat & went & bought a small set of 4 flare nut spanners. Low and behold the 10mm one fits perfectly, only problem is it slipped off the deformed nut so I used a small 6" pair of stilsons/ pipe grips to undo it.

[iangsi]

Just to add to this the correct size of the nuts is master cylinder end is 10mm & 11mm the calliper end, why put different sizes on the same piece of pipe ?

[Robsey]

I presume it depends if the pipework is retro-fitted / repaired or original,

And if retro-fitted / repaired, whether OEM or whatever was available nuts were used.

Thinking back to my 9mm quote - maybe I was thinking of the nipple spanner size.