Uhm, obviously you've never been in the situation i was in. I found myself doing about 15mph down a not-steep-at-all grade in traction conditions where the engine being in ANY gear would cause the drive tires to lock up. What the #### do you want me to do?
And i know it was bad to hold the clutch to the floor like that, but I think the clutch brake was pretty much destroyed before I ever picked this truck up anyway.
I'm guessing he just cant get the timing of the whole double clutching thing down. If you dont time it right it just wont work. It has to be boom boom, just like a heart beat.
The amount of pedal to use depends on how much of a POS you're driving. The trucks in my school had to be pushed down almost all the way because the clutches were so badly adjusted, but any truck i've driven on the job has a reasonable adjustment where you barely need to push it at all.