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I've been at my wit's end trying to solve my back pressure problem. I had resigned myself to putting in an E3D. But on Sunday morning I had an epiphany. Regardless of how much pressure I put in ensuring my ptfe tub was firmly in place, it would work loose after a while. I had rebuilt the hot end three or four times to try and diagnose what was going on.
My theory was the wire whip put extra pressure on the ptfe tub rocking it just a tiny bit throughout movement. Soft filament would fill the tiny void and slow push the tube up. More photos of the result of back pressure https://drive.google.com/open?id=0B3Htq ... URBM2FQMGs

I decided to try removing the ptfe tube from the wire whip. This allowed the whip and the tube to move independently. That had an issue of the tube getting caught on the endstop screws. My next move was to loosely attach the tube to the whip with zip ties. Now there is a lot less pressure on the tube during movement and I have not had the back pressure problem in two days of printing.

Hope this helps someone.

Is this still working out for you? Seriously starting to lose my mind with this back pressure issue. Too many failed prints now.

Make sure the retraction settings in your slicer program is not excessive, apparently anything more than 1mm is excessive with the new hotend as well as the E3d.

Actually it looks like you didn't follow the instructions to insert the Bowden tube into the mesh on the wire whip. There doesn't appear to be a problem if it's installed correctly.

Jim

Hi Jim,
I must not have communicated well in my first post. It was inserted into the wire whip. The only difference between reliably pushing filament through the heat break and it backing up under the end of the ptfe tube was removing the tube from the whip.
I have been printing pretty non stop since this change without any back up and jamming. If you look at all the photos of capped off filament, they all had the tube running through the whip.

It's just a guess, but, I think it's far more likely that you originally didn't push the bowden in further after installing the retaining clip on the hot end the first time. Then you could get melted plastic blocking the path and causing problems. When you reassembled things you probably got a better seat of the bowden tube.