Extruder Idler – too much resistance Pretensioning ?  

Active Member


I have upgraded from the i3mk3 to the MMU2S. I did complete a few first layer calibrations. However I can now not get the filament to extrude.

What works:-
* MM2S loads filament from at least two different spools.
* IR calibration
* Step 31 Filament Alignment check (3A MK3/MK2.5 Extruder Upgrade)

What does not work, p 7.3 First Layer Calibration, p18 - https://prusa3d.com/downloads/manual/prusa3d_manual_mmu2s_eng_1_00.pdf
Print heats up, does the 9 probe the bed, then tries to load filament.
Filament goes from tube to extruder. But after a few attempts either:-
1) filament is retracted and first layer completes with our extrusion, or
2) filament is not retracted but no plastic is extruded on to the bed. (Extrude gear does turn)

I did notice on the build, Step 33 – Pretensioning the Extruder-idler-mmu2s, That the tension is massive, even with the screw just biting the nut.
I have tried the first layer calirbation, with pretensioning the extruder high and low. Note, even with the tension at the lowest (screw just biting the nut), when completing the IR calibration, the filament needs some non-moderate force for the filament to get pass the idler.

Any suggestions on what I am doing wrong ?


Posted : 22/04/2019 1:43 am
Antient Member Moderator

A number of users (including myself) have this problem, which appears to be a firmware issue.

Currently the solution seems to be running firmware version 3.6.0 and with light tension on the screw. The MMU firmware for both 3.7 and 3.6 is 1.0.5.


Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 22/04/2019 11:51 am

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