Sounds like the MC may have lost most/all it's fluid during parts replacements. So during initial bleeding with all that air in the lines, the MC piston could have gone into an unused (rusty) part of the cylinder bore and damaged the seals. [What bleeding method was used?]

Next time you can prevent Master Cylinder Fluid Loss from any/all open line(s) by first blocking the brake pedal depressed. (It only takes an inch or two on the pre-ABS 240s.) The MC piston seals will then block off the reservoir ports so it can't drain. Disconnect the battery to keep brake lights off.

I made a wooden prop that hooks to the bottom edge of the pedal and bears against the 240 seat adjuster bar. It's handy for checking brake lights too.

Bleeding sequence and method used may have played a part too, as well as the new LF caliper*.

*Your new rebuilt LF caliper may have been assembled wrong. We've seen several cases where the OUTER half belongs on the other side of the car. It will look OK and fit perfectly but internals are upside down. It will be impossible to bleed the air from the lower-outer cylinder.

Look at the top of the LF caliper, at the line where the inner and outer halves meet. If you see a "dimple" (punch mark) next to the joint line on the outer half — it's wrong.

The factory puts punch marks on the bottom of each half, so they can be matched correctly when rebuilding. But sometimes the rebuilders aren't careful enough to check for the matching marks.

Believe me, it happens.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.