240d limited clutch pedal travel problem

[derburger]

There's a strange problem with my 1980 240d's clutch system. With its engine running and clutch pedal pushed all the way in, you can't shift out of neutral gear. But with the clutch pedal pushed halfway in, you can change gears. There is a very limited area in the clutch travel where you can change gears easily, making the car difficult to drive. Instead of pushing the clutch pedal all the way in to shift, you have to hit this magic zone in the clutch pedal travel. Also, this magic zone moves around.

I bought the 240d with a leaked-down clutch hydraulic system and replaced the slave & master cylinders with ATE & FTE parts. My clutch bleeding method is to use an oil can on the slave cylinder nipple, leave the clutch master dangling, pump the can until no more bubbles are seen in the reservoir, bolt up the clutch master and close the slave cylinder bleed nipple. I found that pressure on the master cylinder push rod blocks fluid flow, and had to bleed the system without the clutch master mounted. I think the system is fully bled.

I've tried adjusting the master cylinder push rod eccentric bolt to no effect, but haven't done the crazy MB adjustment method where you connect the master cylinder to a bottle of water and compressed air yet. I think it has the correct master cylinder push rod (yellowish plastic tip) but there is a longer black one (supposedly for w126) I could try. The W123 haynes manual says to have 1mm play in the clutch pedal before resistance is felt, but who knows if that is accurate.

What could this clutch problem be? I'm not really familiar enough with clutch systems to know if it's a hydraulic issue, pressure plate issue, or even an internal transmission or linkage problem.