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MMU2S jamming on unload for certain filaments  

New Member
MMU2S jamming on unload for certain filaments

There seem to be a number of people suffering from the filament getting stuck when the MMU2S tries to unload but searching the forums, I haven't found a consensus on how to solve this. My extruder jams with certain PLA filaments and not others. I usually run stock settings but have tried altering the filament advanced settings regarding increasing cooling moves and speed but it hasn't helped. The filaments develop a little hook on the end and get jammed above the bondtech gears. In the photo you can see the filament has been forced to the side. I have no problems with loading but frequent jams on unloading. Anyone got any advice on what might be causing this and how to sort it?

Posted : 03/11/2021 4:20 pm
Active Member
RE: MMU2S jamming on unload for certain filaments

I have the same problem since months. I observed several times, that the extruder is running in "load" direction while the MMU2S tries to unload the filament. Thus, the filament is drawn into the extruder instead of unloading.

Posted : 21/11/2021 1:25 pm
Ruda M.
New Member
RE: MMU2S jamming on unload for certain filaments

Try to look at the screws tensioning the MMU assembly (, step 32). If they are loose, the MMU does not pull the filament enough and the extruder pulley could do this glitch. 

Posted : 23/11/2021 4:16 pm
George P
New Member
RE: MMU2S jamming on unload for certain filaments

As someone who used to have a lot of issues with my MMU2S not unloading filament. Not sure if this is was just a coincidence but I read somewhere about adding a heatsink (had some explanation about causing it to bulge unevenly) to the extruder motor when I was trying to figure out how to fix issues with the unloading. So I added two heat sinks and this was like a year ago, and since then I have not had any unloading issues. I use the stock profiles on PrusaSlicer. 

MMU2S Extruder Heat Sink

The only changes I have done to the MMU2S, other than adding the heatsinks are using the Auto Rewinder for the filaments. The only change I've made to the printer is using BuildTak sheet to the plate. 

I just set up another printer at work with an MMU2S, and after the first print, it had issues unloading the filament too (single colour). So going to try the same thing by adding heatsinks to the extruder on it and report back in case it helps.




Posted : 30/11/2021 8:27 pm