Not V8 related but clutch related

[Coops]

have a problem with my truck,
clutch slipped 2 weeks back and it went in for a new clutch,
i went to pick it up and they said they had issues with the clutch as the pedal would not return to top with out help sometimes, advised its either slave or master cylinder, was on order but i could use the truck until part was in,
BUT on the way home while accelerating up the slip road to pull out onto the main road when i went to change into 3rd the pedal went nearly to the floor as in half the pedal was now free play, slowed down and there was a proper pedal again, thought no more and thought slave cylinder,
3 days later went in for slave cylinder, picked it up on the way home similar thing with the pedal happened again, called garage they said ok it defo the master cylinder,
went back in a week later for the master cylinder, on the way home yup same thing again,
if you hold the truck say in 3rd and rev upto say 3k the pedal starts to get free play go past 3k and the pedal drops away to the point the pedal is a couple of inches off the floor which is working, slow down into traffic and the pedal is back at the top as a normal pedal,

Nissan and the garage are baffled, anyone on here any ideas as they are reluctant to drop the box again

[kiwicar]

Hi
the only time I had anything similar it was on a mini, in that case the crank was in two bits, basically there was a angled brake across the main bearing with the thrust bearing, at low speed the crank would "grow" lengthwise as the crank twisted across the brake and push the piston in the slave cylinder back then as the engine, as the engine sped up the crack "settled" back to its normal length and the peddle dropped about a third of the way to the floor.
I have heard of a similar situation with two part thrust bearings where one half of the bearing slipping behind the other and pushing the crank toward the gearbox, then the bearing settles back and the result is the same as with the broken crank.
best regards
Mike

[mgbv8]

Does it do this at those rpm's when the truck is stationary with no engine load ?

[Coops]

just an update got the truck back Thursday,
the new release bearing had collapsed and was pushing through the cover,

they replaced the whole 3 piece assembly again and now all fine,

just need a trailer now we have a working truck