Need to change the Bowden tube length in firmware - Hardware, firmware and software help

RE: Need to change the Bowden tube length in firmware

LarGriff — Sun, 18 Jan 2026 15:30:25 +0000

@raph_38 the setting will be saved to the MMU EEPROM. The gcode file only needs to be “printed” once. The two ways to reset the length are to make, and print, a new gcode file, or to reflash the MMU.

RE:

Raph_38 — Tue, 06 Jan 2026 13:33:09 +0000

Hello, Happy New Year,

I am facing the same problem. I have a Prusa MK3,5S, Prusa Enclosure, and a box for my spools (with auto rewind spool holder, so built-in buffer). If I understand correctly, to change the length of the PTFE tube, I need to create a gcode file on the USB key with the value M708 A0x22 X450 (the length ptfe ). To execute it, start a print job by selecting this file, or use Pronterface. Will the setting be saved directly to the MMU's EEPROM, or will it need to be executed before each print job ? Then, to return to the default value if necessary, is a reset sufficient ?

Thank you for help

RE: Need to change the Bowden tube length in firmware

OldGuyAdventure — Thu, 10 Jul 2025 11:52:30 +0000

Actually, if you flash the firmware you will overwrite the memory blocks where the length is stored also. So always need to keep that in mind. For me I keep the length statement in my gcode as a precaution should I change out my firmware. I just notate the entry as what it is. Also, best to back up critical settings because anything you can not recover in a week is worth backing up. If you are basing your business on digital files backups are critical.

RE: Need to change the Bowden tube length in firmware

miroslav.h4 — Wed, 09 Apr 2025 09:25:09 +0000

Your 384 returned by the M707 A0x22 command is really your about 300mm (exactly 384mm) of fast charging, and not any hexadecimal 900mm! You have to enter the 900mm value there in decimal, i.e. M708 A0x22 X900. The length must be between 341 and 1000mm, otherwise it will not be saved.

RE: Need to change the Bowden tube length in firmware

Voxel3D_NL — Wed, 09 Apr 2025 08:15:10 +0000

Hi,,

Getting back on this, I tried to do the exact same, and I can set it correctly (If I send M707 A0x22 it reports "384" which is hexadecimal for my 900mm bowden length. but, when loading it does about 300mm quickly and then still continues slowly??

Any tips?

RE: Need to change the Bowden tube length in firmware

RedTar — Sun, 23 Mar 2025 05:02:44 +0000

That was it!! good grief all this head ache because I used a small x instead of a capitol X, I'm so embarrassed.

Thanks you guys for all your help!

RE: Need to change the Bowden tube length in firmware

LarGriff — Sat, 22 Mar 2025 19:12:47 +0000

Or you can simply create a file with one line.

M708 A0x22 X450

Make sure to put a Return at the end of the line. Save it as MMU_Change.gcode or whatever.

Print that file. Done.

RE: Need to change the Bowden tube length in firmware

LarGriff — Sat, 22 Mar 2025 19:00:02 +0000

You were doing the right thing, sending it in your startup gcode. It just wasn’t successful because of the syntax.

RE:

3Delight — Sat, 22 Mar 2025 15:19:57 +0000

You can add the following in to the start of your GCode file just the once:

M708 A0x22 X####

where #### is the length in mm. There is information here: https://help.prusa3d.com/article/prusa-firmware-specific-g-code-commands_112173

Or you can send the command via octoprint or Pronterface

RE:

RedTar — Sat, 22 Mar 2025 15:14:44 +0000

Thanks for the reply!

All the research I've done shows a small case x IN front of the final number that's why I used a small case x. ill try a upper case x but I'm still not sure how to send it to the mmu. I've been putting it in the start up g code file and then re-slicing the part and loading it on to my usb drive, then i load that usb drive into the printer. but nothing seems to happen or change. what do I need to do the send that change to the mmu?