iRobot Roomba 8xx 9xx CHM gearbox cleaning
Roomba 8xx 9xx CHM cleaning
How to clean Roomba’s CHM gearbox
How to disassemble and clean iRobot Roomba 800 & 900 series vacuum robot CHM gearbox?
8xx & 9xx models are better designed for dust seal of its gearbox, but still dust and hair enters it causing it to stop working or even damaging its gears.
To avoid damage it is recommended to clean the CHM (Cleaning Head Module) from time to time, especially if you live in a dusty and with pets environment. Cleaning the gearbox is needed in case you hear strange noises while it is working or in case it gets very hot or stuck.
The CHM module includes a motor and it holds the 2 rotating kind of brushes called extractors. The mating point of the extractors to the gear mechanism has a square shape for the dark gray extractor and a hexagon shape for the light gray one. These extractor’s ends transfer power from the motor and relies on plastic to plastic friction. These mating point are not sealed proof, allowing some dust & hair to pass through the gap straight to the gear mechanism.
Dust and hair build-up on the gear wheels causes it to slow down and increases friction until it stucks and even prevent the motor to spin. In addition, this friction causes extra worn to the parts.
In order to avoid this situation, it is advised to clean the CHM gears and housing. Cleaning frequency depends on usage and the amount of hair/dirt buildup.
In case your Roomba extractors stopped rotating and/or you get the error code #2 (“Uh-Oh” + 2 beeps), it’s time to clean.
Start with the extractors. Clean it by taking off each of the extractors and clean the metal pin and the inside of each flexible tube. If you have cleaned both but it is still not working, it is time to go deeper and clean the CHM and gearbox, hoping the motor is not damaged.
Let’s start the step by step disassembling and cleaning process of the Roomba 8xx / 9xx CHM gear box.
Note:
This guide shows the Roomba 865, but it is relevant for other 8xx and 9xx models as well that uses the same CHM.
DISCLAIMER - Important!
- Phillips head screwdriver
- Used (or new) toothbrush or some other small brush
- Lithium grease
- Vacuum cleaner (not mandatory but recommended) Use it in each step where you find dust and hair buildup but be careful not to vacuum small parts as well.
Note: since most of the screws are screwed to plastic bosses, it is advised to use hand screwdriver for fine torque control.
1. Place the Roomba top down on a solid work surface.
Remove the screw from the rotating side brush and gently pull it out.
2. Unscrew the two screws of the battery cover, take the cover out and pull out the battery holding it in its two side tabs.
3. Unscrew the two bottom plate screws and take out the bottom plate.
4. Remove the bin. Press its knob on top side and pull it out.
5. Unscrew the CHM 4x screws and pull it vertically out.
6. This is the CHM – “Cleaning Head Module”. Top and bottom side view.
Open the red extractors’ frame by pushing inside its yellow latches and raise it. Remove the two extractors.
More images of the CHM that show different areas that I’ll address in next steps:
– Mating areas of extractors. Pay attention to the small printed signs of the cradle that points to the correct shape of the extractors’ end.
– Right and left CHM sides that shows the connecting arms.
7. Release the spring’s outer ring from the hook. Use a small screwdriver or tweezers to pop it out.
8. Release the two wire harness’ from the plastic hook.
9. Unscrew and remove the PCB fixing screw.
This step is recommended but is not mandatory. The PCB is assembled to the CHM gray cover and though it is possible to leave it there, it is more convenient to work while it is disassembled. See image in point 13.
10. Release the silicone dust sleeve’s front flange.
Gently pull and separate each of the silicone flange holes surroundings where it clasps the relative pin/rivet.
Releasing the sleeve’s flange will allow the dust sleeve to be separated from the CHM gray frame in next step. See point 13.
11. Disassemble bottom side (extractors side) connecting arms.
On right and left side unscrew and remove one screw of each arm. Pay attention to the opposite side of each arm where its edge snaps into a designated place.
12. Detach top side (motor side) connecting arms.
On right and left side unscrew and remove one screw of each arm and detach it by releasing its snap. Pay attention not to break the snap.
13. Separate the two main CHM parts.
Do it gently taking care not to break any part and push the silicone sleeve inside to help the separation process.
After separation you’ll end up with the two main parts as seen in the image which shows the gray frame with its PCB connected and the black extractors’ cradle/motor part.
14. Reaching the gearbox.
The gearbox is located right to the motor. In order to reach it, disassemble the connecting arm that was detached in one side in step 12. Unscrew the 2nd screw and remove the arm by detaching it from its snap.
15. Detaching the gearbox.
The gearbox which is now seen is attached to the extractors’ black cradle with 3 screws marked with red circles on the image. Unscrew and remove the three screws and separate the gearbox module from the cradle.
Note: The yellow circles marks the gearbox housing screws.
16. Disassembly of the gearbox.
Unscrew and remove the four screws holding the gearbox housing, see the yellow marks in step 15.
Gently pry the four snaps holding the gearbox housing parts until you open it.
Note: Pay attention to the pins next to the snaps, it serves as guides when assembling the gearbox housing.
17. Cleaning the gearbox.
We finally reached the gears and can check and clean it.
First check the gears to find if there are missing/broken teeth. If you find any, this gear must be replaced.
Though iRobot improved the gearbox design compared to previous models, dust and hair still penetrates through the extractors’ mating points to the gearbox. This may cause severe malfunction of your roomba. See images that show dirt buildup on gears and housing.
You can vacuum, clean and extract the dirt from the gears’ recess area only, OR clean and wash all the gears and housing.
After cleaning and drying all parts, lubricate the gears throughly with Lithium grease. Lubricate both sides of gears and the adjecent ones as well.
D. Voila – you now have a working iRobot 8xx / 9xx Roomba with a clean gearbox.
Have fun and enjoy your Roomba, Avi 
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iRobot Roomba DIY Guides by Avi
9-beep fix | power-supply conversion | speaker fix
5xx-7xx CHM cleaning | 8xx-9xx CHM cleaning
Red CHM mod | Gray CHM mod | battery rebuild
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Thank you! It’s hard to find good info about the newer models.
I am getting error 2 after about 6 inches of travel. I have cleaned everything, even run it without the extractors at all, and cracked open the gearbox to find it rather pristine, and put in a known good battery. I just can’t figure out what else to do except buy a new chm to replace my clean, well lubed one :). Any ideas?
Thank you Robert
Sorry for earlier reply. it was a mistake.
Roomba 8xx Error 2 means: Roomba’s main extractors can’t turn.
Open Roomba’s extractor frame and clean extractors.
Remove and clean Roomba’s extractors and caps. Clean Roomba’s side wheels of hair and debris.
If that does not help consider cleaning the gears.
Good luck
Hey, great effort on cleaning the brush deck extractor gears. in the 800-900 Roomba models.
Thank you vic,
it is an honour to receive such a feedback from Roomba’s guru.
Thank you, Cheers and Happy new year