Master Cylinder fittings

[Challenger in NC]

Anyone know if the front reservoir threads are 9/16" or 1/2"? The tube fittings I have measure 1/2" for rear and 9/16" for front, the rear one threads in fine but I cannot get the front one started. The end of the threads do not appear to be damaged. I'm wondering if the threads on the M/C are both 1/2" or is 9/16" correct but the fitting is being stubborn? Also, the rear fitting only threads in part of the way and stops. These are S.S. fittings. M/C is a disc/drum, original 70 model.

[JH27N0B]

Off the top of my head I think they are 1/2-20 and 9/16-18.
I'd have to dig up some old paperwork to confirm.
Getting the line fittings lined up correctly to start tightening up can be a chore regardless of whether they are brake lines or fuel lines.
In the case of master cylinders, I find having the master cylinder "loose" as opposed to bolted onto the booster, or firewall plate in the case of manual brakes, is the method to use. Get the lines started, then bolt the master in place. With the master cylinder already installed, then trying to get the line fitting to start threading, can be an exercise in futility!
You mentioned stainless steel, that material in brake lines can be a real pain to get to tighten properly without leaking due to its hardness.

[anlauto]

  yes all good suggestions there

[Challenger in NC]

I thought about attaching the lines before attaching/tightening the M/C but the lines had enough give in them to get the fittings very close but maybe i will go back and give it a try. Im also wondering if i should purchase steel lines since i hear so many issues about trying to make the stainless leak free.

[benguin]

I did refresh/replacement on the main and rear lines this year, and following some tips on this board for SS lines, I put a bit of lube on the back side of the line and tightened it down, backed off a bit, then fully tightened.  The vendor indicated this helped prevent galling of the line, and I had no issues with the SS or the old steel lines (luckily).

[JH27N0B]

You need to be real careful if you use lube on brake line fittings.
Anything petroleum based is incompatible with the seals used in brake systems.
Maybe some silicone grease would be ok.
Red grease is great for getting fuel lines to fully seat. Brake lines it's too risky.

[Challenger in NC]

You need to be real careful if you use lube on brake line fittings.
Anything petroleum based is incompatible with the seals used in brake systems.
Maybe some silicone grease would be ok.
Red grease is great for getting fuel lines to fully seat. Brake lines it's too risky.

What about copper based anti-seize?

[benguin]

You need to be real careful if you use lube on brake line fittings.
Anything petroleum based is incompatible with the seals used in brake systems.
Maybe some silicone grease would be ok.
Red grease is great for getting fuel lines to fully seat. Brake lines it's too risky.

Totally agree!  I should have been more specific!

[Challenger in NC]

It turns out 9/16" is correct, it was being difficult. I had to push the fitting in kind of hard while twisting it to get the first thread to engage. The rear fitting still does not engage as deep.