This post gives a detailed description, with photos and reference to a Parts Diagram, of how to replace a Dyson Slim DC18 Undercarriage. The Undercarriage would require changing if part of it broke since parts cannot be obtained individually. I changed mine when the Air Input Changeover Valve Actuator broke.
“Since I first published this article, in February 2013, I have had plenty of feedback from readers and I have gleaned information from statistical data which has encouraged me to improve it. So if you came here soon after I published it you should find better information now. You will also find some photos of repairs carried out by readers of this post in Step 10.” — Helpful Colin
Diagrammatic Breakdown of a Dyson Slim DC18
NOTE: As a consequence of finding the parts diagram above, I have renamed parts in my description to conform with it.
My Dyson Slim DC18 Undercarriage Problem
I wrote this article after I had a problem with my Dyson Slim DC18 where the rotating Air Input Changeover Valve in the Undercarriage didn’t work. Its purpose is to change the airflow from the Cleaner Head Assembly to the Hose Assembly when the DC18 body is lifted and locked into the upright position. A piece of plastic on a moving part of the undercarriage which should engage and operate the Changeover Valve mechanism had broken off. On investigation I found it necessary to replace the entire undercarriage, to fix it, because I could not buy an individual part.
I obtained the new undercarriage for my Dyson Slim DC18 from espares a UK online parts store. (I’m sure parts can be obtained from other stores worldwide.) They asked me for a review. You can find it here under Reviews of Dyson Undercarriage Assembly for DC18 dated 10 February 2013.
“Across the pond (in the USA) you can get parts from ereplacementparts.com. They have a nice site with exploded parts views for many products.” — Andrew Pardoe (25/08/2016)
Dyson Slim DC18 Undercarriage
For those who don’t know what part is the undercarriage this is it:
The Dyson Slim DC18 undercarriage is separate from the body and does not include the Barrel Wheel and Yoke Assemblies. The one above is taken from my Dyson Slim DC18 and has a broken Changeover Valve Actuator which would otherwise operate the Changeover Valve when the Dyson Slim DC18 is raised or lowered.
Removing The Old Dyson Slim DC18 Undercarriage
The main components of a Dyson Slim DC18 are:
- Main Body (Duct Assembly and its parts).
- Rotating Brush Head or Cleaner Head Assembly.
- Barrel Wheel and Yoke Assemblies.
- Cyclone and Bin Assemblies.
The tools required to work on a Dyson Slim DC18 undercarriage are:
- 3mm Flat Screwdriver (to remove e-clips).
- 6mm Flat Screwdriver (to prise open the electrical socket).
- Pliers (to replace e-clips).
- Hexagonal Bit Driver for the following bits.
- TX-STAR security bit T8 (for one screw).
- TX-STAR security bit T15 (for all but one screw).
Some of the tools above were obtained from Maplin. Unfortunately that store has closed so I cannot link to it. – HC
Most DIY and hardware stores sell similar tools. e.g.:
The component parts of a dismantled Dyson Slim DC18 with the tools for working on it:
NOTE: A new undercarriage doesn’t include the Barrel Wheel and Yoke Assemblies.
The Barrel Wheel and Yoke Assemblies include:
- Barrel Wheel.
- 2 × e-clips.
- Cleaner Head Assembly mounting point with Pipe Seal.
- 2 × Outer Wheel Hubs.
Dyson Slim DC18 Undercarriage Replacement Process – Steps 1 to 15
Start by removing the Cleaner Head Assembly and disconnecting the flexible hose at the back as per user instructions. Then follow the 15 instruction steps below numbered 1 to 15.
1. Uncouple The Yoke & Undercarriage
Before removing the Undercarriage the Yoke Assembly has to be uncoupled from it by withdrawing the Axle that passes through the centre of the Barrel Wheel. The Axle passes through the Yoke Assembly, the Undercarriage and the Barrel Wheel and holds the three components together.
To access the ends of the Barrel Wheel Axle pull off the Outer Wheel Hubs. There are two ways to do this:
- curl the tips of your fingers around the edge and pulling them off. (Some force is required but the plastic seems to be strong enough.)
- release the cleaner from the upright position, using the foot peddle, and lay it down on the floor as in the picture below to expose the lugs on the Outer Wheel Hubs (as described in the comment submitted by Rachel Hall). You can then use a long screwdriver to assist in pushing the lugs through the hole in which they are located.
Once one is removed you will see more clearly how the four springy plastic lugs in the centre of each Outer Wheel Hub holds it in place. They are clicked into a central hole.
The Outer Wheel Hubs can rotate but only come into contact with the floor when the cleaner is leaned over to the side. This happens when the cleaner is leaned over to go along a curved path.
When the Yoke Assembly is detached it becomes easy to access the four screws which hold the Undercarriage to the Main Body Duct Assembly at the front. There are two other screws which are accessed from the back. DO NOT UNDO ANY OF THESE SCREWS YET. Wait until instructions 5 and 6.
2. Undo the T15 screw and remove the Swivel Cover.
The cover holds the Female Connector Housing Assembly (electric socket for the Cleaner Head Assembly) in place. Winkle out the socket and split the black plastic of the socket into two pieces (they are not glued but clip together). Only the cable and pins in the socket will pass through the holes in the undercarriage, so take the electrical pins out of the black plastic cover and observe carefully how this socket is assembled.
“Take a picture to show the wire colours so you can put it together again and maintain electrical safety.” — Andrew Pardoe (25th August 2016)
You may need a 6mm flat screwdriver to prise the clips open on the socket cover. Be careful. Excess strain on these clips may snap them off.
NOTE: There is no earth wire going to the Cleaner Head because there are no metal parts with which the user can come into contact. The principle of Double Insulation Class II keeps users safe from the live electrical supply. Also the supply is AC (Alternating Current) which has no polarity. So I cannot see that it matters which way around the live and neutral wires are placed in the Cleaner Head Socket. The issue is more one of mechanical convenience. By that I mean the wires are short, tight and conveniently assembled by the manufacturer and I suggest it is best to put them back in the same way so that they don’t become damaged.
For those who feel there is a safety issue with the polarity of the wires just make a note of which way around the colours are, or take a photograph, before dismantling the socket. In the UK and EU the wire’s colours are blue and brown, and in the USA I am informed by Ellem Kay (see comments dated 9th July 2017) that blue=white and brown=black. Thanks Ellem.
3. Remove the Cleaning Head Assembly Pipe Seal which prevents the pipe dropping back through the socket.
Pull the Pipe Seal out of the socket it sits in and stretch the seal so that it can be pulled over the ridges on the end of the flexible pipe. There are two ridges on the pipe and two matching grooves in the seal into which they engage. The seal sits in the socket and is prevented from rotating in the socket by teeth similar to those on a gear wheel. There are teeth on the seal and teeth on the edge of the socket which engage with each other. See the picture below to understand how these parts fit together.
4. On one side of the undercarriage there is a Micro-switch which senses when the cleaner is locked in the upright position.
NOTE: Before removing the Micro-switch you may wish to go to Step 7 and remove the Barrel Wheel and Yoke Assemblies to gain better access to this switch.
Remove the cover by unscrewing the screw with the T8 bit and then pull the switch out of the housing together with its wires.
A rotating black plastic cam (part of the Micro-switch Cam Assembly) moves under the lever of the switch to operate it when the DC18 is stood in the upright position. Examine this closely. The cam is spring-loaded and in my new undercarriage the spring was not inserted correctly and so was not applying a force to rotate the cam and push it up under the micro-switch lever.
Consequently after reassembly the upright position wasn’t correctly detected. I had to dismantle part of the Undercarriage to fix the problem. The spring should rotate the cam to push on the switch lever. So the cam should not be floppy. Check it with the switch removed. The cam should want to move into the visible position under the action of the spring which is out of site.
5. Remove the four screws holding the Undercarriage to the bottom of the DC18 body (Duct Assembly) at the front using the T15 bit.
6. Then remove two similar screws that hold the undercarriage bracket to the rear of the DC18 body (Duct Assembly) near the flexible hose connection port.
7. Remove the Barrel Wheel
Do this by prising off the e-clip on one end of the Axle. Do it by inserting a small (3mm) flat screwdriver in the gap between the e-clip and Axle and twisting. This stretches the e-clip, against its springiness, to a larger diameter so it will come off the Axle. Note how the e-clip sits in a groove on the Axle.
The Axle can be pulled out from the far side, the Barrel Wheel will drop free and the Yoke Assembly will come away from the undercarriage.
The flexible connecting pipe is part of the Undercarriage so they are replaced together. Effectively the Undercarriage is in two parts the Undercarriage and the Yoke but only the Undercarriage with the small wheels and red foot pedal attached is replaced here.
Ease the wires and Micro-switch out of the holes in the undercarriage taking careful note of how to re thread them.
Return to Step 4 if you were at that step.
8. Commence reassembly using the new Undercarriage
Carefully thread the Micro-switch and wires back through orifices in the plastic. During reassembly it’s difficult to thread the cable back through the small orifice in the undercarriage shown below:
My advice is to temporarily attach a drawstring, using a clove hitch, behind the cable retainer’s flange and bind the drawstring and wires with electrical tape. Be sure to keep the drawstring straight. Don’t wrap it around the wires or it will cut into them when you pull hard. Bend the longest wire back on itself so that the two connectors are not side by side (to keep the bundle slim) and tighten the tape around the soft flexible plastic flange of the cable restraint so that the whole form is as thin as possible. Then thread the drawstring through the small orifice and use it to pull the cable form through. Don’t tie the drawstring to the small hole in the cable retainer’s flange – it may rip open. See below:
“Alternatively get a pair of locking forceps to thread through the hole. Just make sure to grab onto the rubber mount assembly instead of the pressed-on brass connectors.” — Andrew Pardoe (25th August 2016)
9. Take the barrel wheel axle with an e-clip on one end and thread it through the hole in the outer piece of the Yoke.
Then engage it with the Undercarriage, the Barrel Wheel, the other side of the Undercarriage and the outer piece of the Yoke on the other side. Then fit the second e-clip by squeezing it onto the groove in the spindle with pliers.
10. Ensure that the grey peg on the undercarriage lever engages with the slot in the transparent disk.
If it doesn’t exgage it can’t rotate the Air Input Valve when the DC18 is moved between the upright and lowered positions. It was this peg that had snapped off which was the cause of my problem.
Repairs Done By Readers of This Post
Some people have opted to repair this lever and commented about it.
Below is the picture sent to me by Bob Harris:
And here is some of Bob’s email:
“A couple of snaps of the finished job are attached which is still working perfectly. I gather chuck used glue whereas I went with two 8BA countersunk screws (remember BA threads?).Part of an email from Bob Harris dated 16th April 2016.
The red paint is simply because I couldn’t lay my hands on my Loctite at the time and serves just as well as a bit of extra protection against anything shaking loose. As you can see there isn’t a lot of spare space but there is enough if you use the right screws.”
Bob has also left a comment under the name Borris dated 14th March 2016.
Below is the picture sent to me by Adnan Kitchener of Ontario, Canada, who sent an email as well as a comment dated 25th November 2018:
11. Refit the upright position detection Micro-switch ensuring that the cam functions correctly.
See Step 4 above. Hold the cover in place with the T8 screw.
“Fitting the Micro-switch cover can be awkward. It can get covered up when the undercarriage is in certain positions.”
12. Reassemble the connectors in the Cleaner Head Assembly socket and place it in its housing.
Then fit the Swivel Cover over it and hold it in place with the T15 screw.
13. Now check that the Undercarriage mechanism functions.
Don’t force anything to work. Dismantle parts and refit them if they don’t operate correctly. Check again that the Actuator for the Input Port Valve engages the slot in its transparent disc and rotates it, when the DC18 is moved between the up and down positions, before attaching the Hose Assembly that attaches to the Wand.
14. When the mechanism is OK refit the Cleaner Head Assembly.
That’s so you can pick the DC18 up and stand it in an upright position.
With the DC18 upright:
- Reconnect the Hose Assembly that attaches to the Wand.
- Connect power and carry out a Suction test at the end of the hose.
Check the air valve changes the air input from the Hose to the Cleaner Head Assembly when the DC18 is lowered. Do this by Checking there is suction through the Wand/Hose when the DC18 body is locked in the upright position but not when it is lowered.
Check that air is being sucked in through the Cleaner Head Assembly when the DC18 body is lowered:
- switch OFF,
- remove the Cleaner Head Assembly,
- switch ON and check for suction at the Cleaner Head Assembly connecting port.
If there is suction:
- switch OFF and continue with Step 15 below,
- else investigate the problem.
15. Finally replace the Outer Wheel Hubs.
Just align the fixing lugs on each Outer Wheel Hub with the central hole on either side of the Yoke Assembly and push evenly on the outer surface at the centre of the Outer Wheel Hubs until their lugs click into place. If not already attached, connect the Cleaner Head Assembly and wand. Perform a functional test.
Further information can be obtained from “the unofficial dyson forum“.