I think they can last a very long time, or no time at all, it depends on the use and the driver.
In my 1 ton with low gears I would imagine the clutch still looks near new after about 10,000 miles because you don't need to slip the clutch hardly at all to get moving.
In a truck with tall gears and or a poor first gear ratio a clutch disc may not last as long.
Not a Stovebolt, but I had a 95 VW with 235,000 miles on the original clutch, no signs of weakness or slippage. Then a "friend" borrowed the car for one evening and ruined the clutch. Obviously it was not far away from happening any how, but I bet there was another 10 to 30 thousand miles in it if I hadn't had any "help"..
The operator makes a big, probably the biggest, difference in clutch life.
Grigg
