I have an 04 Accord that I cannot figure out why the clutch won't engage. I've replaced both the master and the slave cylinders and bled the system, by hand and with a vacuum pump. The first half of the pedal travel still feels as if there's a bubble trapped somewhere, but after literally hours of bleeding, no air has come out in quite some time. What could be the problem? I have another vehicle that you have to raise the back end of the car after bleeding and bleed again so that the bubbles move around and work free, should I try this? Any help would be greatly appreciated.

 

It would make more sense to me to raise the front end of the car to let all the air flow upward towards the bleeder screw.
Try it like that, or your way too.
How are you bleeding the system?
Pump about 5 times, hold it, open bleeder screw, allow fluid to come out, tighten bleeder screw, release pedal and repeat?