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Sure its the linkage itself,and not the pressure plate?--or the throwout bearing dragging on the collar on the tranny it rides on?(tranny loose or misaligned,or the transfer case "foot" tightened too much and putting strain on tranny mainshaft can cause the throwout bearing to drag instead of slide easily--collar can rust fast too if truck sits a lot!)..
Pressure plate might have something jamming in it(piece of crud,bolt,socket-

or a broken lever thats binding(does it chatter?)--or it might be the disc is in backwards--I did that once!

--and it was so much fun to do twice I vowed I'd burn it before I ever put another clutch in it,after 2 defective pressure plates on my 72 K5 I had...

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That "Z" bar that goes to the frame bracket and ball stud on the block sometimes bends the flat stock bars on it that are just butt welded to the "pipe" part of it..I ripped my hair out on a guys 71 chevy K20 plow truck,we put a brand new clutch in it--it was perfect for a week,it plowed a few storms fine--then the pedal started sticking to the floor,and you had to "help" it up with your toes..clutch would not release all the way either when fully depressed..--we tried adjusting it,it was still in adjustment..we could not beleive it lasted only a week..after we checked the transfer case foot mount,and loosenned it some(mechanic used a 1/2" impact on the bolts--squashed the rubber mounts too much--that alone seemed to help a lot..
But as I watched him put the clutch in and out,I noticed the "Z" bar pipe was moving,but the flat stock peice that the linkage rod to the fork goes on was just flexing and bending!--and his cab was rising up and town too,due to rotted body mounts!---we zapped on a small peice of flat stock to "gusset" the flat bar thing,and it was perfect again..after 4 hours of freezing our butts off in the cold..

we darn near pulled the new clutch out !.. so keep looking,it might just be the rod from the pedal to the "Z" bar is rubbing on the cab due to the body lift or something simple like our problem was..(hopefully--good luck!)
