Saturday, February 27, 2010

Replacing the electromagnetic clutch brushes on a Micra CVT

Soon after buying my first automatic transmission car, a ten year old Nissan Micra (K11) with the CVT gearbox, I found that the carbon brushes which supply power to the electromagnetic clutch tend to wear down.

The clutch operates (as far as my limited understanding goes) by passing a current through some kind of magnetic powder (maybe just iron filings? Anyone know what this is?) which fills the gap between the driving (engine-side) and driven (gearbox/wheels side) plates. When the engine is at idle, no (or very little) current is passed through the powder so the engine spins without transferring force to the driven side.

As you hit the throttle and engine speed increases, the current passed through the powder is raised and the powder becomes magnetised, sticking together more strongly and transferring more of the rotational force from the engine to the wheels.

The electrical current is supplied by a pair of carbon brushes which rest against turning discs (I think they're called slip rings, which just slot onto a splined axle), since you can't just stick a wire into something that's constantly spinning. After a while, both the brushes and the slip rings start to wear down - hopefully the brushes more and the rings less, since the brushes are easy to replace while the slip rings are probably almost impossible (i.e. cheaper to buy a new car than to get the clutch out, open it up, replace a part, put it back together and re-install it in the car, argh). When the brushes wear down, springs in the brush holder push them further out until a certain limit, they either lose contact completely or periodically slip out of contact briefly, triggering the "N-CVT" warning light on the dashboard. As they wear out of reach of the clutch wheel/slip disc arcing can occur which is apparently a bad thing, too.

So anyway, my Micra had started to get sluggish, needing more revs than before, and I figured it might be the clutch brushes. I checked the web for similar problems and solutions and found a LOT of problems and NO solution other than buy a new brush holder/new gearbox/new car.

Nissan refused to talk to me on the phone, telling me to call local dealers instead. Two separate dealers quoted me a laughable €218 for the whole brush holder assembly, which is apparently all they will give you short of an entire new clutch (again, more than the cost of the car).

This seemed a lot of money when it was just the carbon brushes which had worn down. So I took the brush holder assembly out anyway.

Where is it? Here, on the front of the transmission bell housing:
(edit, new pic to help locate it)

You can disconnect the power plug by pressing a tab on the left side of the upper half and pulling it upwards. Blurry closeup of power socket:

The hole down into the clutch after removing the brush holder. Looks... not so great:

And the brush holder after removal:

Knackered. Right down to a stub on the engine-side brush and while not so bad on the driven side, the spring was jammed up with cruddy carbon deposits and failing to push the brush out to maintain contact with the slip ring.

So I disassembled and cleaned it (on the left is another brush from a mk3 Ford Fiesta's broken alternator... similar!):

The brushes looked so similar to what you'd find in an alternator, serving the same purpose anyway, that I went to a shop ("Electro Maintenance" in Baldoyle) to find something suitable. A guy came out of the back room and took the disassembled holder away before coming back with some Delco alternator brushes, for which he charged a pretty reasonable €7. He also suggested that I snip off the old brushes, leaving just the bit of wire that was somehow attached to the metal mount, and then solder the copper wire of the new brush on top of that. Before doing this, we threaded the old black plastic insulation piece onto the wire, fed the spring through and cut off the excess wire (to stop the brush from falling out the end of the holder!).

Soldering the new wire onto the bit of old wire (no idea how the old wire is attached to the metal so nicely but still conducting current):

And reassembled after soldering:

Note the slight slant in the brush faces where they contact the clutch wheel/slip rings - the longer edge is on the bottom and the shorter edge on the top (where the power socket is pointing). This is what the wear pattern in the old brushes looked like, so I oriented the new ones in the same way (if I'd bought brushes without a slanted edge, I might have used sandpaper or emery cloth to file one in, since it probably helps them fit into the clutch properly).

Also, if you have a multimeter, check the continuity from pin to brush for both pairs. Each pin should form a circuit to the brush on the same side.

After installing the brush holder (much easier than removing it, bizarrely - it took about 5 minutes of gently sliding it around and twisting to get it out, after removing the battery and its tray* and moving a relay box out of the way), I sat in the car and gingerly started the engine. It fired up, and I listened for any horrible scraping noises and watched the N-CVT lamp on the dashboard, which didn't light up. Knocked off the engine and did a self-test of the gearbox (put it in D, ignition on but don't start engine, brake on, accelerator on, cycle Ds-D-N-R-P, accelerator off, brake off, start engine) which reported okayness (N-CVT indicator flashes one long, then seven short and repeats).

* Note: I recently checked the brushes again and was able to get the holder out without removing the battery or its tray. If you have the right screwdriver or a ratchet with screwdriver bit, you can get it out in less than 10 mins! I did have to lie under the car and ask my SO to hold the ratchet end in place though.

I carefully reversed and turned from the cramped shed into the cramped laneway and drove home. Feels a bit more responsive so far but I was literally a 2 minute drive from my house so no chance to get it up to speed.

Hopefully the fix is ok and won't trash the clutch or wear down within 2 weeks - time will tell. (It'd be pretty funny if it completely failed within a couple of days :/)

Replacement from Nissan: €218
DIY hack job with alternator brushes: €7 + time (one hour if you're smart, 4 hours messing about if you're me).

Hope this helps anyone in the same boat!

Update 26/10/2011: it worked fine for over a year and a half, until...

...Until I stupidly drove through at least a foot of water in a flood on Monday (yeah, who'd have thought it might rain in Ireland). This seemed to short out the coil and some kind of safety interlock started switching it off despite my repeated attempts to stop and restart it. Eventually after an hour or so hanging around near where I'd parked the dying car, it managed to get going again, albeit warning me that the clutch's coil circuit was shorting (IIRC, the fourth flash during the self-test mentioned above).

If I'm lucky, either the brushes have simply worn down, or a bit of trapped water is occasionally making a short in the connector. If not, water may have leaked into the clutch and contaminated the powder or something, I don't know. That hole is near the bottom of the engine, so for all I know the bell housing has a pool of water in it, bathing the clutch and promising rust or some other disaster.
I wonder if it's the same type of clutch used in the older Subaru Justy - it looks like they can lose their powder, which would not be good.

Finally got round to removing it, which just took a couple of minutes this time - amazing how much easier some jobs are in direct sunlight rather than in a dark garage. Last time I removed the battery and its tray and pulled a bunch of stuff out of the way, needlessly.

Turned out the brushes were hardly worn at all, but they were very wet. When I replaced them last year, the generic alternator brushes may have been slightly too long for the available space, and I was afraid to break something so didn't tighten the brush holder's bolts nearly enough, leaving a gap large enough for water to pour in as I foolishly rammed the car through floodwater.
Might be a good idea to file down the brushes a tad before installing them, enough to push the brush holder absolutely flush in its socket and screw it in tight enough to prevent water entering the clutch housing.


  1. Wow what a fantastic result and a very well put together artical. Did you notice though any sticking of the gear lever when putting it into drive, previous to the repair. It would appear that so many of us have this sticky gear change problem with the cvt and your method is definately on the. To try list.

  2. Hi Dark Lord,

    Thanks! Yes, my car did have a somewhat stiff gear lever before replacing those brushes. However, it's still just as stiff now.

    There's no mechanical connection between them and the gear lever AFAIK - I think it's stiff for other reasons, and more importantly, that stickiness doesn't seem to indicate anything bad.

    Perhaps it's stiff for all of the K11 N-CVT autos - would love to try out one of the H-CVT K11 automatics produced after August 2000 (and before the K12 series in 2003), when they replaced the electromagnetic clutch with a more normal torque converter - the gear lever on them looks slightly different.

    1. Hi there, I have a nissan micra k11 and the cvt light came on after going over a bump I'm thinking it's a loose connection but I have no idea where to start looking? Any help would be gratefully received :)

  3. Thank you, thank you, thank you. Your article was very concise and the pics helped a great deal. My dad's Micra was knackered and I found your blog which helped us greatly. We even went to the same place in Baldoyle and the brushes are still the same price 7euro. With the part in hand all told it took me 35 minutes to complete the job and saved us a couple hundred euro. Thank you for your help.

  4. @Pip, I'm glad it helped! Thanks for your kind words :)

  5. Hi, thanks for a well written article. I had the same problem with my 1998 1.3 Micra. I had to buy the replacement item from Nissan £140 in the UK.
    Mine were nowhere near as dirty (only 40,000 Miles on the clock) as the ones you replaced so i hope the repair will last.

  6. Very good and helpful article.
    Do you have a part number for the Delco alternator brushes please. I have the same trouble on my Micra and came across your article so I am going to give it a try.

  7. So glad i have found this.My mum has the same car 2000 micra K11 CVT and it has been very sluggish taking away recently.After reading your article about the Brushes,i contacted my local dealer,only to be told that they have never heard of the Brush assembly,or replacing them,despite pointing out to them that it is an item that is supposed to be inspected/replaced every 24k, think i'm going to have to contact another Dealer.Thankyou for an excellent article.

  8. micra7:

    Unfortunately I haven't managed to find the box those alternator brushes came in. Once I do, I'll put the part number here.

    Otherwise, you should be able to bring the holder and old brushes (I cut them out first) to an alternator shop and get them to choose suitable brushes.

  9. Forgive me for sounding a bit thick,could someone tell me where the brush holder assembly is located on the Gearbox, when viewing the Engine from the front? i can't locate it by viewing the pictures.Is it quite far down.

  10. Hi epok,

    It can be a bit tricky to locate at first, but it's behind the radiator, on the front of the transmission bell housing.
    If the schematics website wasn't up and down like a yo-yo, I'd post a link to a diagram...

    But keep in mind that the clutch goes between the engine and gearbox, and you'll find it.

  11. Epok: I added another picture before the others, showing its location on a removed transmission.

  12. Oisin,i can't thank you enough for your help.This article,and your assistance has been more help to me than any of the so called ''experts'' in the last 18 months! absolutely superb!

  13. Thanks Epok, glad to hear it helped you!

  14. Hi Oisin,would you happen to know the part number for the brush assembly?

  15. Yes, it's Nissan part number 3005141B00.

    It's component 22 in this diagram:

    Getting a new one from Nissan is pretty expensive, though! I shudder to think what they'd charge for the powder clutch (part 20 on that diagram)...

  16. Well i must thank Oisin again for all the help he has given me,and others by producing this blog.I feel quite stupid now as i have just found out that my car has the H-CVT box,not the N-CVT auto that i thought it would have as it was manufactured in july 2000.I now have a car displaying the same symptoms of sluggish taking away as described here,but no idea how to fix it as this auto box doesn't use the electromagnetic clutch brushes.I am appealing to anyone for help in regard to how i would go about fixing or diagnosing what is wrong with the H-CVT auto box.

  17. epok:

    Awesome, I always wanted to try the H-CVT, which apparently gets better fuel consumption and should be a little faster.
    In that case, your car has a more conventional torque converter (fluid clutch) rather than the electromagnetic clutch in the N-CVT (powder clutch). The properties and common pitfalls/solutions with torque converters are much more well known.

    For a start, you might try two things:

    1) If you haven't done so already, completely drain the automatic transmission fluid and replace it. Not sure exactly what type of fluid is best, probably Dexron IIe or Dexron III. This can make a massive difference, especially if it's not been done for a while - the fluid behaves a lot like brake fluid, so if moisture or other contaminants get into it, its ability to transmit force gets weaker.

    2) Disconnect the battery and leave the car for a few minutes before reconnecting it. This can apparently reset some settings in the CVT controller and make it recalibrate itself.

  18. I have paid a lot of money to my mechanic without any valuable result until I researched the Internet myself and found this article. A solution of few minutes and everything worked well. I am indeed very grateful.

  19. Glad it worked for you John!

  20. Hi people this is the best advice i have found. I have also found someone who is selling the brushes.

    alot cheeper than nissan!

  21. Hi Alison, those brushes look about right. Not sure if the measurements are exactly the same, but it seems close enough. And certainly much cheaper than what Nissan want for the brush holder assembly! Thanks :)

  22. Oisin, You are a STAR I am going to work on it during next week and after Reading all the comments I am sure will be Successful.

    One help Did you manage to find the part number for the brushes or any one else kindly can pass me with part number or measurements . Will be grateful

  23. This gentleman Oisin has done favour to entire community facing this problem We all should wish him the very best

  24. Could you please advise what type brushes should be used i.e
    Carbon Graphites
    Metal Graphites

    1. Hello MFW, that's an interesting question which I'm not sure how to answer, as graphite is a form of carbon. The brushes I got from that alternator shop are still working today, almost four years after installing them! I'm sure if you bring the brush holder to your local shop they'll be able to find suitable brushes.

  25. Did you ever find out what the brushes you used were?
    There isn't anywhere local that I can take mine to get new brushes, it would suit me better to order them online.
    Are they the Lucas a115-a133 brushes listed above?

    1. I never did find the box for the brushes Tristan, but if I need them again I'll keep the number.

  26. I have a new Accent with CVT. Does the gear box produce a slight "clunk" at 23mph as it changes from L to D? Mine does!

    1. Hi Rodger, I don't know anything about the Accent, but perhaps it's a lock-up clutch engaging once the car gets up to speed? Most autoboxes include one of these in the torque converter for efficiency reasons. Or it might not be that, as I'm mostly talking out of my arse on that topic ;)

  27. thank you very much MR.OISIN
    I had small auto shop.but I incounter kind of problem got a niose bleed,hehe but when I open you blogs.I appreceate to your help.thanks thanks,
    GOD BLEES.....

  28. This was so relieving to read. I thought I would have to get an automatic but, now I can fix my manual car. I really like the feeling of shifting and it has been hard since the clutch broke. Keep up the great DIY.

  29. Hi
    I have a 1995 Nissan micra Ncvt 1300 that I love - it has done over 90K Miles and is truly great fun for this 68 year old pensioner wjo drives it very verify enthusiastically, using it regularly on motor club events such as night navs and mini rallies I regularly get 65MPH in the low lock gear that also gives me valuable engine braking down the narrow country lanes - it is truly fantastic and I am unable to break it!! - the gearbox features a powder clutch and was used by the first owner for 18 years and recently only did 7,000 per year form one MOT certificate to the next - Your article was fantastic - I have read it many times and may have to overhaul the gearbox at a future date - meanwhile I have repaired my throttle body, fitted a new alternator and associated belts as well as replacing a Distributor (unnecessarily) and have found the distributor has a disk with a hole in it that is the rev limiter and once blocked should give me 8,500 thus giving me 85Mph - The engine is unburstable - will let you know when it blows up aor the gearbox ruins itself - Long live NCVT!! Norman

    1. Thanks Norman! I'd love to try the 1.3 CVT as it's probably still a relatively light car. Still never tried any of the HCVT versions, they seem very slightly faster and more economical for some reason, even though intuitively a torque converter using fluid to transfer power seems like it should be more wasteful than the powder clutch. Mine is still going strong, although I had to get the water pump replaced a month or two back (cost about €160 at my local-ish mechanic in Coolock, seems fair enough). This fix for the powder clutch still seems fine after nearly 5 years :)

  30. Hi there, I have a nissan micra k11 and the cvt light came on after going over a bump I'm thinking it's a loose connection but I have no idea where to start looking? Any help would be gratefully received :)

    1. Hi Kayleigh,

      Yeah, sounds like either a dodgy connection somewhere, or possibly these brushes are nearly worn out. Mine was intermittently coming on as well before I replaced the brushes.

      Try doing a test of the gearbox and electromagnetic clutch:
      1. Put it in D
      2. Turn ignition to last click without starting the engine
      3. Hold the brake pedal to floor
      4. Hold accelerator pedal to the floor
      5. Cycle gearstick from D to Ds then all the way back to P
      6. Release accelerator
      7. Release brake pedal
      8. Start engine

      After that, the N-CVT warning light should start to flash to indicate self-diagnosis. The list of code definitions is as follows (stolen from "cisco's Micra files" forum --

      "No fault found: There is a 2 second pause, followed by the light remaining on for 2 seconds and then 7 short on/off second blinks.

      If a fault is detected one of these 7 short blinks will remain on longer than the others.

      Fault Code 1 - The first blink is on longer than the others - Accelerator or accelerator position switch circuit is short circuited or diconnected.

      Fault Code 2 - The second blink is on longer than the others - Inhibit switch circuit is short circuited or diconnected.

      Fault Code 3 - The third blink is on longer than the others - Vehicle speed sensor circuit is short circuited or diconnected.

      Fault Code 4 - The fourth blink is on longer than the others - electro-magnetic clutch coil circuit is short circuited or diconnected.

      Fault Code 5 - The fifth blink is on longer than the others - Line pressure solenoid circuit is short circuited or diconnected.

      Fault Code 6 - The sixth blink is on longer than the others - Torque signal circuit is short circuited or diconnected.

      Fault Code 7 - The seventh blink is on longer than the others - ABS signal or idle up relay circuit is short circuited or diconnected.

      Fault Code No Number - Lamp blinks at 4Hz repeatedly - Battery supply fault or memory back-up fault.

      Fault Code No Number - Lamp does not blink - Check all components."

      IIRC, code 4 was appearing for me when my brushes needed replacing. If that's what you get, then happy days. Otherwise it could be more complicated. To be honest, the gearbox is very simple and elegant; far more straightforward than the mess that is a "conventional" autobox. But still, most garages and mechanics won't want to look at it and will probably refer you to an automatic gearbox specialist, which means (in Ireland at least) utterly stupid money, more than the car is worth, even though the fix might actually be simple like in this instance.

      Anyway, feel free to post another comment when the code readout :)

    2. You can get them brushes here...cheaper too
      they are the brushes you need
      .....thats who i found to sell me replacements and listen to what i had to say rather then trying to just trying to sell me anything to make money.
      the guy i spoke to really tried to ensure i got the right ones and helped when i phoned back as the braided copper wire was a tad too short, he told me what id thought of doin anyway and cut the old wirw of the old bushes and solder that on at the end, simple and stronger than the wire if done correctly.

      the brushes you need are E1s and are 8mm x 5 mm and the length is perfect, no problem, know....i did that same repair before i knew there was a guild on here....but to be fair, im a mechanic and my hobby is electronic repairs n upgrades.......ps3s xbox 360s, laptops etc and once worked at a leading electronics company swapping components on circuit boards and resoldering them on by hand. so i had the unit out, brushes swapped and back in in less that 20mins.
      BUT !!!!!!!!!!!!!!!!!!!!! the N-CVT light is still flashing but the car drives fine (or as fine as a k11 drives).......can anybody please give me an idea as im kinda disabled so id rather not spend time bent over an engine bay if someone on here knows why......all help will be gratefully recieved


    3. Hi, did you try the ECU's diagnostic program? If not, follow the instructions I posted in my previous comment and see what pattern of flashes appears on the N-CVT warning light. That should help narrow it down. If it's running ok, maybe the error handler needs to be reset, which might just mean disconnecting the battery for 15 minutes or so.

  31. Hello,
    I also have a K11 Micra, the N-CVT light came today, I was on the "P" position and then pass the "R" to get out of my parking place, I did accelerate but nothing happened, like it did'nt clutch properly. The same thing happened on th "D" position, but I did a big acceleration this time and it clutched, the NCVT light disappeared, I my Micra did the end of the road very normally.
    Do you think it's the end of my NCVT system ???

    THanks for your help

    1. Hi, mine started to do things like that shortly before I replaced the brushes. That was 6 years ago (!!!) and the car has been fine since then.

  32. pouvez vous me donner le site ou vous avez trouvé les charbon pour la boite

    1. Hi Alexis,

      I didn't buy them from a website; I picked them up in an alternator shop in Baldoyle. You should have no trouble finding them online though, maybe with the link Craig posted.

    2. mais ce sont des charbon pour alternateur cela va fonctionner sur une boite auto ? :0

    3. Hi Alexis,

      Yes, they have the same purpose -- to transmit electricity between a stationary terminal and a rotating element (a "slip ring").

      See here:

    4. Hello Oisin!

      I am a troubled (for the time being hopefully) owner Of Nissan Micra 1993, 1.3, 16V (282000 KM and more to go..). Having problems with my CVT gearbox the last month...
      Your guide is great and really helped me so far! I cleaned up the brushes which were a mess but the powder seems to be at very low level.
      Could you direct to where I can find a suitable replacement? Should the powder be specific for my own CVT gearbox?

      Thank you in advance for any information and your cooperation!

    5. Hi Michael, glad you sorted the brushes out. The powder is a different story, which will require removing the electromagnetic clutch and opening it. This sounds like a heavy job which I don't have the equipment or skills to attempt.

      But it's likely that the clutch in our Micras is very similar to that used in the Subaru Justy, which seems to have a bit more info on the net. One CVT repair shop in New Zealand claims to be able to fix electromagnetic clutch problems for about the same price as a manual clutch, which sounds promising...

  33. Thanks for the insight Oisin. I have been looking all over the internet for this powder and have not found anything yet. I hope I will find sth through the threat that you suggested me...
    I will post again if I manage to fix it by myself.

  34. Hi thanks to you I got my Micra fix i got brushes from electric motor from Bosch washing
    mashine bit work to fit but IT is working cost 35€

  35. Hi there my sisters has a nissan micra k11 n cvt 1.3 auto. It judders when slowing and driving off. It's fine when driving. I've taken the bushes out the top of the gearbox. There worn. But not to badly. No light on the dash too. 145k

    1. Hi Sam, haven't seen any of the 1.3 CVTs, they seem pretty rare! Hard to say what the problem is, although since you took the brushes out you may as well replace them anyway. Did you do the diagnostic start sequence to see if the ECU can help localise the problem? Otherwise, it might be time to drain and replace the gearbox fluid, but try not to overfill it.

  36. Thanks for your very speedy reply. I'm a lv3 mechanic in training. I was going to do the bushes any way as they don't seem to worn. Maybe 10mm on on. 140mm on the other.I have access to a snap on ultra at work if that Will be better than doing on the car. And do you know the oil capacity of the gearbox. Many thank . Sam

  37. Dear Guys

    I need used CVT Transmission with Electro Magnetic Clutch from Nissan Micra,maybe You can give me information where i can buy this one. I need for teaching material. Thanks alot

  38. I have taken the burshes out of a nissan micra should thay be covered in oil ?

  39. When I say burshes I meat bushes and I is an auto gearbox that I removed them from please can someone help

  40. As you can see my English is not good I mean brushes


  41. That is some documentary thing you mentioned.That is why I liked the article. I know a lot of people like do not actually know these Clutch Replacement things properly. So thank you so much for sharing these information with us.