Can't stop brake line leaks

[6s855]

I'm having trouble with leaking from the master cyl front brake line fitting as well as leaks from both fittings to the proportioning valve.
Both the MC and Valve have been re-sleeved and rebuilt with new kits.  The MC is an early style that needs both inverted flare brass fittings; straight-thread 3/8 x 24 on bottom and 3/8 x 27 NPT on top.  The NPT fitting seals fine, but the bottom straight-thread weeps past the threads under pressure.  They are both purchased from NPD.  When I measured the OD of the straight it was not 3/8 (.375") but .365" which makes it "loose" when screwed in and apparently will not seal against the MC.  I suppose I could anneal and use a copper crush washer behind it like you would use on a flex hose to the caliper to seal it or ask NPD to get their micrometer out and find me a .375" fitting.  Any thoughts??

As for the proportioning valve, the inverted flare M and R seats  have "scars" from all the tightenings of previous fittings.  I'm using new Classic Tube brake lines, but their tube flares have sharp edges not like the old lines whose edges are flatter and wider.  I'm guessing the Classic flares are not sealing against the "scars".  If there were a way to smooth out the "scars" that might do it.  Or I could sand the Classic flare ends to get a wider flat area to seal against.  But I'm hoping the mechanics on this site have seen this before and help me out.  This is the only thing keeping 6s855 off the road.  Very frustrating!  Thanks.

[Bob Gaines]

I'm having trouble with leaking from the master cyl front brake line fitting as well as leaks from both fittings to the proportioning valve.
Both the MC and Valve have been re-sleeved and rebuilt with new kits.  The MC is an early style that needs both inverted flare brass fittings; straight-thread 3/8 x 24 on bottom and 3/8 x 27 NPT on top.  The NPT fitting seals fine, but the bottom straight-thread weeps past the threads under pressure.  They are both purchased from NPD.  When I measured the OD of the straight it was not 3/8 (.375") but .365" which makes it "loose" when screwed in and apparently will not seal against the MC.  I suppose I could anneal and use a copper crush washer behind it like you would use on a flex hose to the caliper to seal it or ask NPD to get their micrometer out and find me a .375" fitting.  Any thoughts??

As for the proportioning valve, the inverted flare M and R seats  have "scars" from all the tightenings of previous fittings.  I'm using new Classic Tube brake lines, but their tube flares have sharp edges not like the old lines whose edges are flatter and wider.  I'm guessing the Classic flares are not sealing against the "scars".  If there were a way to smooth out the "scars" that might do it.  Or I could sand the Classic flare ends to get a wider flat area to seal against.  But I'm hoping the mechanics on this site have seen this before and help me out.  This is the only thing keeping 6s855 off the road.  Very frustrating!  Thanks.

Did you choose stainless steel lines or original terne steel lines?

[98SVT - was 06GT]

Are you running into the old AN vs Industrial fitting problem? Are the tubes a double flare?
Interchangeability
AN 37° flare and industrial 37° flare fittings function identically. In many cases they appear to be functionally interchangeable, but they are not. What this means is that while the products may look similar, you must not use an industrial 37° flare fitting design as a direct substitution.
http://blog.parker.com/an-37-flare-vs-industrial-37-flare-fittings-whats-the-difference

[6s855]

Not stainless lines.  Stock Classic Tube steel.  They have 45 degree flares.

[Rukiddin]

Brake fluid is not as easy as,say,trans fluid to seal...but the type of connectors must match. Pipe threads are many times just not tightened enough and rarely need any teflon tape,etc,but old threads,old tubing will give you fits! I know from 50+ years of fighting auto repair... Flared fittings have been around a very long time and are very effective.....if everything is right. The flared fittings depend on the pressure exerted on the back side of the tube flare against the surface of mating flare. ( yeah,I know...old news ) what we ASSUME is enough to force the two surfaces together to complete the seal can be affected by a couple things.....You MUST begin with clean threads,both male and female on either pipe,or flare. Never try to use one type of fitting against the other. Ain't gonna work too good. Trial fit threaded types before assembly,if possible. Keep a small box of known good fittings of every auto type if working on old cars. Picture the flare nut ,either old or new,not threading into the designated opening easily as a new nut/bolt assembly. Any interference between theads can ,and will,reduce the required pressure to seal tube to flare. I know,roll your eyes and say "this guy is an idiot if he thinks I don't know this stuff". We all KNOW it,just is overlooked at times. Never assume that because you torqued a fitting that is has reached the correct sealing pressure. Binding threads have caused hours of frustration. OK class..........there is no test today.

[OldGuy]

As for the proportioning valve, the inverted flare M and R seats  have "scars" from all the tightenings of previous fittings.  I'm using new Classic Tube brake lines, but their tube flares have sharp edges not like the old lines whose edges are flatter and wider.  I'm guessing the Classic flares are not sealing against the "scars".  If there were a way to smooth out the "scars" that might do it.  Or I could sand the Classic flare ends to get a wider flat area to seal against.  But I'm hoping the mechanics on this site have seen this before and help me out.  This is the only thing keeping 6s855 off the road.  Very frustrating!  Thanks.

I would replace the inverted flare tube seats that are lightly press into the prop. valve casting. The old seats RARELY seal on different tube flares. They've conformed to the previous flares. It seams that the more you tighten them, the more that they leak.

It is fairly easy to replace the tube seats and they are dirt cheap to buy (like $2/each). Send me a PM if you are interested in going this direction.

Frank

[davez]

I didn't know you could buy seats for the valves. I thought they were part of the casting. Great to know for the future.
dz

[6s855]

Sent PM to Oldguy.  Thanks.  BTW, stopped leaks by using original lines, but obviously defeating the purpose of new lines.  Going thru brake fluid like crazy.