New Z axis stall cause

Had a new/old one. Running a simple carve I've done before. Was in the other room when I heard the carver go quiet. Went in and had a change the bit message. Did it and restarted ok but within a minute or so of text carving it went quiet again. Had a Z axis stall. Reached in to test the truck for movement vertically and found the truck was very warm. Truck was tight and hard to move. Shut everything down, had to leave so left it till later. Got back a couple of hours later, truck was cool and would slide vertically easily. Reran the entire carve and even though the basic carve was 'air' carved had almost the same result. Figured it wasn't the truck rollers causing the stall. Checked the cable housing and it was comfortable to the touch. Had a spare z truck so changed it and ran my carve ok along with the truck staying cool.
Only thing I could guess was the chuck shaft bearings were the heat generators. Managed to find the bearings, worst problem was trying to find a way to support the truck to press out the shaft and change the bearings. Guess I'll find out for sure if I ever use the truck on one of the machines. Definitely kept me from being bored for a while.