Good Day!
Earlier today I started having an issue with the PTFE tube pulling out of the extruder when the filament is retracted, on color changes the AMS then tries to feed filament which just goes openly into the chamber instead of the extruder eventually causing an error.
Has anyone experienced this before? I’m wondering if there could be damage to the connector on the top of the extruder that might be preventing it from clamping tightly.
Thanks!
A couple things come to mind. This style fitting has very fine stainless steel fingers that bite into the tube sort of like fish hook barbs. The colored plastic ring pushes the fingers away from the tube, allowing it to be pulled out of the fitting.
It could be damaged fingers, this requires replacing the fitting. A single aggressive yank on the tube without pushing the ring in can cause this damage.
It could be routing of the tube that keeps the ring pressed in which will keep the fingers from biting into the tube.
And finally, the tube itself could be damaged in the area where the fingers bite. This happens if the tube is pulled without releasing the fingers.
Typically, what we see at work are first and last and most often it’s the tube. We just cut off the damage and reconnect. We have thousands of these, typically with 100 psi air.
Thanks for the reply! That was in line with my thinking, the end of the tube looked pretty rough, there was a clear line where I assume the fitting would be grabbing, I had cut off that portion and it didn’t seem to solve the problem, that was leading me to think the fingers themselves may be damaged in the fitting like you indicated.
Maybe I’ll try a new tube all together, otherwise I might have to replace the extruder assembly as the fitting itself doesn’t seem to be available.
You may want to check out this procedure to change out the Extruder Filament and Cutter Sensor Assembly. There is a bracket thing that may be lightly pressing on the fitting’s ring, holding the fingers out of the way. I tried finding the fitting without luck on SMC’s site, it may be custom.
Bambu may send you this assembly if you ask, it might be cheaper than an entire extruder assembly.
Thanks! Following that I was able to pull the sensor assembly out and inspect it. The PTFE coupler is definitely damaged and the fingers fell right out. I was able to pull the coupler out and replace it for now with the one by the back of the chamber, sure that will cause me some other problem, but wanted to try and run a test which I’m doing now.
Seems that’s the only part that isn’t purchasable on it’s own though.
How did you pull the coupler out? I tried but didn’t want to damage a new unused extruder. It looked like it would come out with just a bit of sideways force.
Yah it’s just push fit in, I had to pry it with small screwdriver and work it out. It’s possible I damaged the coupler worse than it was pulling it out, it was fairly difficult to get out. It extends in the a sort of funnel into the flilament tube by the sensor, it’s possible because it was broken the bottom wouldn’t pull out of that funnel making it harder to get it out as the new one slid in really easily. So far the replacement has been working much better so far. It’s too bad you can’t buy these as it would be an easy fix.
I did realize the one further down the tube is is likely just meant to prevent the tube from pulling back on retraction, It really doesn’t need to be the proprietary one and I can likely just replace that with one of the many generic spares I have…
I think from your description of fingers that lock the PTFE coupler to the tube that I have this problem.
I started with an error stating that I had to pull the filament back from the extruder which ended up with me pulling out the filament sensor in the extruder.
Attached to the filament sensor arm were 2 bits of steel.
I removed these metal fingers and the sensor now moves and operates correctly.
However now the PTFE pulls out of the coupler and does not lock in.
Are these available as a spare part without having to order a complete extruded assembly. ?
They are available but not as a single connector. They sell a 3 pack of the splice connector that’s on the back where you uncouple for external spools. You have to harvest the connector from the splice. I think there’s a wiki on how. I’ll try to look later.
Thanks for the info, I already have these so will dissemble and see how to remove and replace it in the extruder. 
I managed to gently pry apart the spare par adapter that you mentioned at the black end
Once this adapter was replaced with the new one I had removed from the spare tube adapter it was all reassembled and works perfectly.
Here are some pics of the metal that came out of the switch that I believe was causing the original problem.
Thank you for the excellent pictures and write up. It should help others down the road and I’m glad it worked!
The support team finally sent me this link on how to replace it.
Just took them a few days 
I knew I’d seen it somewhere. Watching the first video, if you only have one left and one right hand, how do you get the fitting out? 
Thanks lasermike & Awesomelcey, I ran to this exact issue today and the post and remedy for it work excellent!
Mahalo again!
