Sorry to hijack the thread but I am having a similar issue. 1995 F150 2wd, new clutch, master and slave. Drove like a champ for 2 months then suddenly one day master line popped out of the fitting on the side of the slave. Tried plugging it back in only for it to pop again. Ended up replacing the line from master and master as well as a new clip on the slave. Now the line stays in but I cant seem to bleed it so it works. I finally got the pedal to return with engine off and can put the clutch in and shift gears. However when the engine is on the pedal once again sinks and no gear shifting is possible. What am I missing ?

Basically just like bleeding brakes. I have good luck gravity bleeding the clutch. Take the cap and rubber cup(if applicable) off the clutch master cylinder leaving them off and fill it with brake fluid, then crawl under the truck and loosen the bleeder on the slave cylinder. When the fluid starts flowing, let it run for a while until several ounces run through making sure the master cylinder never runs dry. Hope this works for you.

This is an old thread that after the last post goes back to 2014. I came across this information that may give you some ideas of what is going on. I have no experience with your issue but maybe this will help you. Sandy https://www.yourmechanic.com/article...vin-sunderland

I did bleed it 5-6 times now, even tried vacuum bleeding with a bleeder - no change

Thankyou, I have checked all of the areas I could but sadly slave is inside the bellhousing so no go there.

why is is shifting with engine off but not shifting with engine on

Because when the engine is off the input shaft on the transmission is not turning. If the clutch was releasing properly it would shift with the engine on.

well crud, the truck towed around 6k lbs the day before but did so without any issues. The next day I get the clutch problem, less than 1000 miles on the clutch.