Clutch Master Cylinder Failures

[johnanc]

Experiencing several clutch master cylinder failures (cracking occuring adjacent to fillet strengthening the boss accepting hydraulic line) following replacement of dual mass flywheel with Heath single piece flywheel kit flywheel, friction and pressure plate). Also replaced pilot bearing, fork, pivot assembly, throwout bearing and slave cylinder at same time. Replaced hydraulic line after first master cylinder travel (line only support at right hand upper bellhousing bolt). Last couple inches clutch pedal travel (both application and release travel) stiff. Have used GM and other brands master cylinder, all have same markings so appear made by same manufacturer.
Other related threads read but don't seem to offer answers.

[a5150nut]

Did you remove the clutch line from the master before changinge everything? If not, ANY movement on that line will cause the master to crack. I know! Had to drive surface streets across San Jose in rush hour traffic because it broke at work the day after changing the starter. The master is plastic and won't stand for any abuse. Glad I can shift without a clutch.........

[johnanc]

I've changed out three of them in the last month (first was original 210K miles, lucky for me the other two were lifetime warrenties. Have been more careful with the last two during roll pin insertion. Using "Cobra" brand waterpump pliers to put minimal pressure on other side of roll pin boss. If it's true it's just not being careful enough during line/roll pin installation I'm happy. Thanks for the tip. John
(Trailer trucks are a lot easier for me to shift without a clutch then my pickup!)