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.

[Turbo Al]

Did you do all the work yourself or did a shop do it?. What year is the truck I assume 1992 to mid 1994. I have never had a master fail just the slaves, and always traced back to something wrong with the pivot ball. My 1993 has an access hole (small one) for greasing and with a good flashlight you can observe the action of the thow out arm etc while someone else pushes on the clutch pedal. IF all the parts are correct and installed by you I suspect the throw out bearing may have come part way off the throw out arm. Does greasing it make a difference?
Al

[unionparkhobby]

I had the same problem it was caused by the pivot ball being worn down. It has a grove worn in it causing excesive travel. I cracked three before finding the problem. I replaced the pivot ball and it worked for me. But you said you already replaced it. I wonder if the fork is worn. Good luck.

[johnanc]

I did the work myself, started driving it about a month ago. I installed new fork, release bearing including pivot ball assembly. Greased everything before assembly. It's going apart to see what's wrong. Thanks for the advice though.