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Replacing Conductor Plate in 722.6 Autobox

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by umblecumbuz, Sep 10, 2015.

  1. umblecumbuz

    umblecumbuz Senior Member

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    Your Mercedes:
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    My 722.6 autobox (W203 220) has been playing up, and after a few weeks research I concluded that it was the conductor plate, so I decided to change it.

    After removing the undershields, I drained the gearbox (5mm allen key on a socket - drain plug is tight) and replaced the plug, took off the heatshield protecting the electrical connection from the ECU, then removed the sump (Torx No 30, six bolts - again tight), being careful to hold it level when lowering it as there was still some fluid in the pan.

    Next, I unclipped the electrical connection (anticlockwise tag on pilot bushing, then it just pulls free) and went to remove the pilot bushing, which required a 7mm socket on an extension. The photos will show the details. And there I hit a snag. I have changed these before without a problem, but this one would not undo. The brass threaded insert that it screws into, which is embedded in the conductor plate inside the gearbox, just rotated with the setscrew. Finally, as I was going to replace all the affected parts, I decided that it had to be broken loose, so I undid the ten bolts holding the valve body (same torx as sump), and forced the body with conductor plate out of the gearbox housing. If this problem ever arises when the intention is just to replace the pilot bushing, it will become a major strip-down job, instead of a £9 replacement! The conductor plate was shot, and you can see where I had to break it to get the whole assembly out of the gearbox. (Pics 1 and 2).

    Once on the bench, acting like a surgeon for cleanliness, I removed the solenoids with their retainers, keeping these in strict order so that everything could go back correctly. Then I was able to remove the conductor plate from the valve body by springing two plastic clips, one on either side. With this dismantled, it was easy to check each solenoid by touching each one with 12 volt leads to make sure they ‘clicked’ as they should. (Pic 3).

    Everything had to be meticulously cleaned, and I used a copious supply of lint-free cloths, plus an aerosol brake cleaner. Before the solenoids were fitted to the new conductor plate, I made sure that every contact was clean and shiny, without any ‘burn’ marks which would indicate poor connections.
    I then cleaned the sump, checking the condition of the fluid as I did so. No traces of metal or dirt of any kind were found (not surprising - the fluid was changed only 10k miles back). There was no magnet in this sump, and the plug was not magnetic either. (Pics 4 and 5).
    Continued ...
     

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  2. OP
    umblecumbuz

    umblecumbuz Senior Member

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    Then I undid the lower banjo connection from the front oil cooler and drained a little more fluid.

    When offering up the reassembled valve body and conductor plate assembly, care had to be taken to ensure that the sliding valve on the body mated with the pin that is operated when you move the gear lever (just seen in one photo). With this in place and torqued up, I fitted a new pilot bushing, lubricating the two O-rings on it with ATF. This only needs to be nipped up with the 7mm socket, so as I was tightening it I also pushed hard on the bushing to make sure it eased into its home. Any undue force will strip the tiny brass insert and then you have real trouble. This bushing can only be fitted in one position, so I carried out a dummy fitting first while the assembly was on the bench. My old bushing was not leaking at all, so I saved the O-rings just in case. (Pics 6 and 7).

    Interestingly, the electrical connector to the ECU has a tiny hole drilled into its base - just seen in one photo - and this allows air to be introduced, thus breaking any possible capillary action which might wick fluid up onto the ECU in the event of a leak from the gearbox. I can’t remember seeing this on an earlier connector. (Pic 8).

    To refill with ATF, I measured the amount that I had drained off by pouring the old ATF into plastic milk containers. Then I used identical containers, cleaned out and blown dry with an airline, marked their levels to match with a pen and refilled with exactly the same amount of fresh fluid, adding a small allowance for fluid lost while cleaning the sump, etc.

    After a good run to get the gearbox hot I rechecked the level and adjusted it as needed. Fortunately it all worked without a problem, with smoother and seemingly quicker gearchanges. Back went the undertray, after rechecking for leaks.

    I started the job at 8am, and finished without hurrying at 3pm, after several coffee breaks, lunch, and time out to consult my notes.

    The cost was £141.89 for all the components shown in photo from OneStopGearboxShop, and £63 from Opie Oils for ATF (MB 236.14). So, with a useful amount of ATF left over, just under £200 for the job. (Pics 9 and 10).
    Unfortunately while I was grubbing about under the car I saw several maintenance jobs that soon need to be done. There’s always something, isn’t there!

    RANDOM NOTES
    Gearbox clamps. One of these differs from the others. This one fits nearest to the pilot bushing and also carries the small heatshield.

    Any stored codes that relate to the transmission should be cleared on reassembly, so that false readings do not interfere with normal operation.

    After the initial fill with ATF, cycle through the gearbox with the engine running and foot hard on the brake several times over a period of minutes before adding the final amount of fluid.

    When reinstalling the solenoids on the conductor plate, using the sprung forks to hold them down, make sure that the forks do not impede the movement of the solenoid plungers.

    It almost goes without saying that surgical cleanliness is needed throughout, and normal clean rags should not be used for wiping down components, because they can leave almost invisible lint. Only lint-free cloths should be used (ask your local printer - they always use lint-free wipes).
     

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    Last edited: Sep 10, 2015
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  3. Naraic

    Naraic Moderator

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    Now a sticky.
     
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  4. Ian Parkin

    Ian Parkin Senior Member

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    Whats the symptoms of a failing conductor plate?
     
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  5. Flyinspanner

    Flyinspanner Senior Member

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    Your car often will only stay in second gear when you place it in drive.
    Reverse may be ok.

    I think it may often the speed sensor on it which may fail, so signal to change up a gear is lost, - the ECU then uses second gear as a 'limp home'. - don't drive it fast in this situation, as it will heat up the ATF fluid, and could overheat it in extremist. Possibly causing other damage.
     
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  6. television

    television Always remembered RIP

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    And another, when the speed plate fails it stays in second
     
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  7. Arudge

    Arudge Senior Member

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    Great to see your back Malcolm.
     
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  8. bob 6600

    bob 6600 Senior Member

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    That post is 15 month's old
     
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  9. Arudge

    Arudge Senior Member

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    I've absolutely no idea how I managed this, can my post be removed as it's clearly not appropriate?
     
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  10. bob 6600

    bob 6600 Senior Member

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    Haha don't worry, you're not the first and won't be the last :D
     
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  11. Sheridan07

    Sheridan07 New Member

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    Thanks very much for the excellent write up on the 722.6 transmission very helpful.
     
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  12. Sheridan07

    Sheridan07 New Member

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    Forum is a mine of information lots to learn thank you.
     
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  13. Westheath

    Westheath Senior Member

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    onestopgearbox on ebay are not using MB OEM conductor plates as advertised imho.

    We ordered 8 different plates across various suppliers on ebay including those advertising Genuine OEM,
    all were the same with the part number MB and marque etched out.
    Prices varied from £140.00 to £50.00
     
    Last edited: Dec 17, 2017
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  14. alexanderfoti

    alexanderfoti Moderator

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    I bought one from one-stop-gearbox-shop on ebay, it was a genuine plate with the MB logo and PN.

    However, I would say that the non genuine ones have the logo/pn ground off then they are probably all the same, being made in the same factory and the none genuine ones are likely of the same quality.
     
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  15. Arudge

    Arudge Senior Member

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    As a manufacturer we do not sell our surplus stock, it's always destroyed. But we do take in orders for parts for older vehicles. We are about to run parts for DB7, maybe 200 bumpers, less than a days work. The tooling is supplied to us and we run the parts.

    What I'm trying to illustrate is that just because it's not come from MB doesn't mean to say it's not OEM. Although I'd of thought selling MB marked parts on the secondary market, not an MB approved outlet was a bit naughty, and a breach of copyright, which probably why we destroy surplus to order.

    Be nice to see an image of the attempt to delete the trademark though.
     
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  16. alexanderfoti

    alexanderfoti Moderator

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    Likewise, they are probably both made on the same run.
     
  17. Westheath

    Westheath Senior Member

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    The problem I had, when we did the research, was the advertisement on eBay showed the conductor plate with MB logo and part number etc, the plate received had these scrubbed off the same as the other cheaper plates and the part was identical to the other units.

    onestopgearbox are saying MB are removing the markings themselves ???
    That's the official response from them in an email I received.

    Hello

    thanks for your message, our conductor plates are OEM and come from Germany, as you can see this is taken straight from our description:
    "Brand new Mercedes Automatic 722.6 Gearbox Conductor Plate, Side Connector (including O rings), Oil Filter and Bottom Pan Gasket.

    This auction is for 6 parts in the picture.

    The conductor plate is a Genuine OE Mercedes Part. The other parts in the kit are o.e.m. quality aftermarket parts.

    All Fit the 722.6 Automatic Gearbox, this Gearbox is fitted to most rear-wheel drive Mercedes 1996 onwards."

    As you can see it perfectly says right there that the other parts in this kit are OEM QUALITY not genuine OEM this was written in the parts description so if people wanted to buy it they can see that the only genuine OEM part is the conductor plate we are sorry that you think it is not OEM but we pride ourselves when we say it is OEM as we buy this in specially from Germany in this instance as we test and the parts and can see that these are the best option out there for money not only for customers but for us a company.

    Mercedes Benz have started to scrub off the labels due to copy-write issues if we send parts out with their logo on there can be issues i can show you a photo of the parts side by side that I have taken but we send the conductor plates out now without the logo and OE part numbers on, sorry if you have an issue with that but unfortunately we have to protect ourselves as well.

    Best Regards
    MJ
     
    Last edited: Dec 20, 2017
  18. Frontstep

    Frontstep Senior Member

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    What a waste to destroy the surplus stock.
     
  19. Arudge

    Arudge Senior Member

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    You would be appalled at what gets thrown away, absolutely appalled.
     
  20. Uncle Benz

    Uncle Benz Senior Member

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    I would have thought it unlikely that Mercedes manufacture this part themselves. It is very likely to be another manufacturer producing them for Merc and putting the part number and logo on. Then indeed it would need to be erased to sell the part directly. I have seen this before with parts manufactured by Febi-Bilstein where the BMW roundel has been ground off. If you look at Mercedes parking sensors for example you will see both Mercedes and Bosch part numbers on them. If you buy direct from Bosch the Merc number is absent. I think the tie up means for a number of years the manufacturer cannot sell the part directly themselves, but obviously the 722.6 transmission is pretty old now. Still damn good though!
    FYI, the same electroplate is also fitted to automatic versions of the Porsche 928 iirc
     

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