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Old 10-09-2015, 01:57 PM
umblecumbuz umblecumbuz is offline
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Default Replacing Conductor Plate in 722.6 Autobox

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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Old 10-09-2015, 02:02 PM
umblecumbuz umblecumbuz is offline
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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 by umblecumbuz; 10-09-2015 at 02:07 PM.
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  #3  
Old 10-09-2015, 02:15 PM
Naraic Naraic is offline
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Now a sticky.
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Old 23-02-2016, 03:59 PM
Ian Parkin Ian Parkin is offline
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Whats the symptoms of a failing conductor plate?
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Old 23-02-2016, 06:04 PM
Flyinspanner Flyinspanner is offline
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Quote:
Originally Posted by Ian Parkin View Post
Whats the symptoms of a failing conductor plate?
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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Old 23-02-2016, 06:51 PM
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And another, when the speed plate fails it stays in second
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