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722.6 Slow shifting: fixed today by replacing trans conductor plate

13631 Views 26 Replies 6 Participants Last post by  Dave2302
The silver S430 has been getting a lot of TLC from yours truly. This stuff is fun. :)

The transmission's shifting felt kinda sluggish. It's never failed to shift, and it's not in limp-home mode, but the shifts would feel just slightly klunky--no banging noises, just a feel--and it was starting to get very gradually more mushy, if you will. There were no codes. It'd probably be fine for another 10,000 miles, but I just don't like sloppiness on a Benz. Better to deal with it sooner, when I can take my time and do it right.

Some Googling and STFF'ing said something about the speed sensor typically causing this, and the way to deal with one of those on the 722.6 transmission is replacing the conductor plate with a new one. Since I already had a plate handy, I thought, might as well try an experiment.

Sure enough, it worked. Shifts did firm up considerably, which I consider a good thing. The "klunky" feeling is pretty much gone. I had done the transmission fluid and filter exchange (the full 14 liter version) about 5,000 miles ago, and apparently dropping the tranny pan really does result in a loss of nearly exactly 4L of fluid. Four more liters of the good stuff took care of things. Also replaced that made-in-Taiwan Meyle filter with a genuine M-B filter, as well as a new trans electric connector (also M-B brand). Hey, those have to come out anyway, so might as well, right?

The job took me about 5 hours, since it was my first one, and as usual, I'm doing it on the street, i. e. no lift. Actually, since my buddy's borrowing my jack, I did it with the car's front end up on a pair of Rhino Ramps. :) Yes, it can be done. It's a little awkward getting the valve body back in, especially if you have long arms, but it's certainly doable. Next time, it'll probably take me about 2 hours since I now have a better idea of how to do it.

While I was at it, I checked the resistance of the solenoids. All of 'em are right within spec; matter of fact, they're at dead-center of the acceptable range.

Miles on the car are 143K. Tonight's test drive was a pleasure. Well, driving that car always has been, and now it's even more so.
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Sorry to sound like "The Prophet of Doom" here, BUT, here's what I'd do, (being a Semi retired Auto Trans Specialist) .........

Make sure Oil Level is correct first.

Clear out all Faults and Events, drive the Car for a few minutes / days and see what comes back, they just may be old codes caused by someone working on the Car before :wink

If you keep getting Ratio Errors, Speed Implausible, Slipping etc then get a known good used Tranny and Converter, or get Rebuilt Units fitted by a good Transmission Specialist :wink

In my experience you will most likely be wasting your time and money fitting Parts to this Transmission ............

Not always, but 99% of the time :wink


Cheers Dave
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Well that's certainly not what I wanted to hear! I appreciate your advice, but for a couple hundred bucks for a conductor plate I might just have to try it. I thought surely the diagnosis would be to try that.

No, sorry but I disagree .........

That is "chuck parts at it until it's fixed", and IMHO that seldom ends well, and always costs far more than proper diagnosis. It gets very very expensive very quickly :wink
Proper diagnosis is, first clear all codes, then see what comes back..........
Then, check all 'relevant to fault codes(s)' resistances at the external Trans Connector, and if faulty, remove valve block and check those components ............. So far this has cost nothing ..............
What if you replace all these parts, and then the same codes are there ??
"Oooooops, I've replaced the Conductor, the Solenoids, Plug, Oil and Filter, and it's still the same, oh dear, must be the Wiring to TCU or TCU itself" ..............
What about the 'slipping', that indicates Worn Clutches or Torque Converter breaking up internally.
If you pull the plug from the Trans, it should still Drive and Reverse without slipping :wink

See what I mean ?? :wink

Proper Diagnosis is eliminating everything else at minimal cost until you know exactly what is the faulty component :wink

I'll post back in a couple weeks when I'm done and give you the opportunity to say, "Told ya so!" 锟斤拷

I would never do that :devil
I'll be happy if you tell me it was the Conductor Plate, but I'll be very surprised if it is just that, and you will be in the elite 1% "dead lucky" bracket, and on that day I will suggest you go buy a Lottery Ticket :wink

I'll do what Dave said and clear the codes this weekend and see what comes back.

Yes, do that and I can advise you further on what action I'd take, if your Car was in my Workshop :wink

Thanks for your help, guys!

No Proberlermo :wink


Cheers Dave
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Just got back from the road trip. 1,600 miles later, I can now report for sure that the new conductor plate *did* fix my issues. The transmission shifted very well the entire time, and it feels good 'n' solid. Matter of fact, the entire car feels solid. I guess that's what happens when one actually fixes issues on his car. :)

That's great news, and isn't it a nice feeling when you've ironed out all the issues and got on top of the Car :wink

So, apparently I should buy a lottery ticket. :-D

Ahhhhh, not really !!

Your Trans was only given "Routine Maintenance", it didn't have a ton of Codes, or Slipping when you started :wink
TBH, I would think in your specific case, that the new Oil Filter and fresh Oil will have made the biggest difference to its performance :wink

Cheers Dave
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I'd still like to drop the pan and see if there's anything in there; that would be a sure sign. I have the $12 electrical plug, so I'll replace that while I'm under there.

If it's not the TC, how likely is it I'd be successful "rebuilding" the trans? I've rebuilt 3 engines, done some heads, cams, timing belts, differentials, etc. I've got all the normal kinds of tools, including torque wrenches and gear pullers.
Or should I just get a rebuilt or junkyard one, which would be quicker.

First up, Trans and Converter must be done together, do not change one without the other, it usually results in more grief than it's worth, and you will end up doing it again using both parts :wink

To rebuild a 722.6 and Converter properly costs me 拢900 in parts.
3 hrs R&I, 1hr Road Test, back on Lift, Leak Check, Oil Level Final Check
8 hrs Strip Clean Inspect Rebuild.

There is a load of special tools needed to do this properly

To Rebuild and Fit I retail at @拢1600 + depending on exact vehicle.

If I were a DIY and good with spanners I'd buy one with a Guarantee from a Breakers, pref low mileage, in UK around 拢450.00. If your breaker is honest about "good" and "mileage" you can fit and forget :wink

You MUST flush out the Oil Cooler and Lines.............

A couple of "Kooler Clean" Aerosols are a good DIY, we have a special Air Powered pulsating Paraffin Flushing plant :wink


Cheers Dave
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:laugh , I'm 55 years old and DO light 'em up at times :wink

I have W220 and W203 with 722.6 and both cars do creep slowly on flat ground.

The Supercharged Jaguars with 722.6 drive pretty much the same (Trans Wise) as the Mercedes, just slightly different Shift Points Programmed into TCU :wink

They also suffer from all the usual 722.6 problems, which is no surprise really as the Trannys are Identical :wink
Interesting at that time that Jaguar felt ZF couldn't build a trans to cope with the S/C Jag's Torque :laugh

Mind, they still can't, Audi and BMW (ZF Trans), they are regular visitors with Trannys gone "Bang" :rolleyes:
And when they go, boy are they "lunched", busted sun shells, drums, gear sets etc etc :big laugh:

Cheers Dave
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Wally is correct, you can't really get an accurate stall figure for the MB due to the Electronics stepping in.

It's irrelevant here anyway.

If the Converter is breaking up, then the Trans will have some form of contamination / wear, and Vice Versa.

This is why a decent Trans Specialist will never change one without the other, unless of course the Converter has a cracked weld on a foot or some such, but even then they will be Extremely Specific on what exactly is covered by any Warranty they offer :wink

It just isn't good practice, and usually comes back to bite your @ss :wink

If I could drive this car I could tell him exactly what is wrong but this is years of Transmission Experience, and a "feel" thing.
No amount of Videos, Fault Descriptions etc etc can make up for "Seat of the Pants and Under the Right Foot" senses :wink

But, from the "it almost gets to 2000 rpm to pull away in 1st or 2nd Gear", (assuming of course that it is actually in 1st / 2nd Gear, and not stuck in 3rd or 4th), it is a 99% certainty that the Trans and Converter needs replacing. And if it is stuck in 3rd upwards, with "No Codes and display indicating 1st / 2nd", then it is likely a complex internal fault beyond DIY Capabilities / Equipment and Cost Effectiveness (LOL is Effectiveness even a proper word) :grin.

The most economic solution for a DIY guy is Good Used :wink

Cheers Dave
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