1977 XS400 front master cyclnder replacement

Ramsey Salim

XS400 Member
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Maryland, US
Hello All
1977 XS400, 11K miles
The ask: What font master cylinder replacement do you recommend for my motorcycle?

The details:
The original front master cylinder was corroded beyond repair.
I bought two types of replacement master cylinders, one 16mm bore and another 12mm bore. They are the universal type master cylinders (less than $20).
The issue is when I press the lever, the brakes engage with the disc, but the level continues to go all the way down to the handle.
I bled the brake line as much as possible, using a vacuum line at the bleed nozzle to remove every tiny air bubble.
My next assumption was that the front calipers were not good. So I replaced the calipers with original rebuilt ones. It's the same issue; the lever goes all the way down, even though the brakes were completely bled.
I'm assuming that the issue is with the master cylinder.

The "ask" again: Is there a replacement front master cylinder anyone recommends for my type motorcycle. URL links would be greatly appreciated.
I would like to keep the cost low, since I am working with a limited budget to restore my motorcycle.
If you are 100% certain you have no air what so ever in the brake system (have you checked for small bubbles in the MC reservoir when lightly applying the brake? Turn the handle bars so the the MC is more or less level.) take a look to see if the brake hose is moving as you apply the brake. Old brake hoses are known to 'expand' when pressured up causing a spongy feeling or even bottoming out the MC. I've seen this on cars as well as my '78 build, my front hose was moving quite a bit and brake lever would bottom to the handle bar, new hose solved the problem.