CD30043

In the am when first started and underway, my c300 shifts from 2 to 3 in what I may come close to describing as a slip. I've driven a car before that truly did slip between gears and its not the same but maybe best described as a weak shift. It does it every time without fail. The conditions are uphill grade about 25 degrees, light throttle, since I'm in a residential 25mph area, and it will only do this on the first shift. When leaving work to go to lunch or home for the day, the condition will not replicate. I'll be due for a service in about 2.5k so I was going to mention the condition. I'm thinking it will be called normal, but it truly does not feel like something that is normal. Any ideas?

Acapulco Bill

You should ask your MB service advisor to check if the TCU has the latest software upgrade (2010 ands before for sure need this), and improves the shifting.

However, many feel that a lack of pressure on the plates is the cause of this slippage. There are upgrades to the 7G that tuners for the C63 use, replacing the valve bodies and changing the TCU software. Here is a thread about this:

https://mbworld.org/forums/c-class-w...nsmission.html

As for shift patterns, in fact the 3 to 4th gear shift should be the worst, as two sets of plates have to release and grab. There is a chart that says which set(s) of 6 plate pairs activate for each shift. Will be posted later. Perhaps it is just a single valve body that is not applying sufficient pressure.

If this is the case, the entire valve body assembly has to be replaced, and re-marrying a new set of valve bodies to an individual transmission is a complicated process.

Acapulco Bill

I am in error, the shift chart clearly shows that the worst shifting case is between 2nd and 3rd gear (not 3 to 4th).

So it appears that the valve body that pressurizes the K1 plate applies insufficient or slow pressure, as plate B2 remains in contact. Here is the chart of plates and shifts:

CD30043

Bill, thank you for the input. I have been following the threads about transmission issues, and I am at least fortunate to only be 23k into the 100k CPO warranty. As far as the chart, I'm normally not too dense, but would you please provide some guidance as to how it should be interpreted? When my service is due, I plan to ask the dealer to keep the car overnight so that the issue will replicate.

I believe that any transmission issue is best handled by the dealer, especially the full drain at 39k.

Acapulco Bill

Each of the 7 plates, B1-B2-B3, BR, K1-K2-K3 drive one combination of gears that provide a ratio of rotation. All final gear ratios (second column), is result of the rotation sums of three sets of plates being linked together, transferring the energy from the engine's input to the torque convertor, at different ratios to the final drive shaft.

There is a logic to this madness. First gear is only accessed in Sport Mode (C or E mode always starts in second gear). The colored boxes represent application of positive pressure to the plate.

So going in Sport Mode from 1st to 2nd requires the release of pressure from B3 and applying this pressure to B1. So the shift is almost instantaneous, as the pressure release/application takes place within a gear "set" (B in this case). When driving in C or E, one always starts in second gear, which is in the B gear set.

Shifting from 2nd to 3rd however, requires releasing the pressure in the B1 plate and transferring this pressure to the K1 plate. The "worst case shifting scenario" is where the driving gear receives its pressure from the release in another gear set. This also happens in the shift from 5th to 6th, however if this were hard acceleration one would be going 100 MPH.

Shifts from 1-2, then 3-4-5 and also from 6-7 are more seamless because the changes happen by reapplying pressure already in a plate set, B or K.

So if the shift from 2rd to 3rd is lumpy or hesitant (and lets face it, ANY gear change the 7G is just too lethargic and slow IMO), then K1 isnt getting this pressure or B1 isnt giving it up. In any case it is the valve body assembly which performs this.

Make sure that your 7G DOES have the latest software upgrade first. If STAR indicates that your 7G's TCU has the latest, then demonstrate to the Service Advisor the shoddy shifting your transmission performs.

CD30043

Bill, clearly understood. Thank you. Is it at all logical that the shift issue manifests only at initial startup and takeoff? Would there be some sort of pressure bleed off if the car sits for 12 hours, for example? Today on initial start, I gave it a bit more throttle and the condition would not replicate. Of course, I did not have to concern myself with kids waiting on the school bus, but perhaps only an errant Jehovah's Witness running around.

Acapulco Bill

Yes, it could be that this behavior only appears when the transmission fluid is cold, or a valve body opens or closes slower when cold. If it is difficult to duplicate consistently, perhaps one should forget it until the 39k fluid transmission ATF fluid and filter change.

After that, if this slow 2 to 3rd gear shifting reappears and consistently, then perhaps the valve bodies should be replaced under warranty (and it is an extremely difficult task to marry the valves to the plates). Even so, if the shifting is better after driving a few miles, then one could just live with this knowing that after warm-up, everything goes back to normal.

Jurgeenh

have you ever solved this problem?, my car its doing this same gear change, but it apear sometimes 2nd to 3rd and always 6th to 7th its like a flare, if i drive faster it will not ocur on any gear, only during light aceleration it will flare, i got new oil and filter mi car is 50k miles and its been doing it since i bought it at 25k

Acapulco Bill

@Jurgeenh: That quote was from 2012. Since then, in 2015, had the ATF and filter changed @ 33,500 miles (a bit early, but was in for a B Service at my most trusted shop in Las Vegas, so why not?). Now two years later just had another B service with an oil change in between. NO OTHER SERVICE AND NOT A SINGLE REPAIR ON THE W204 AFTER ALMOST 8 YEARS. The 722.9 still behaves the same, apparently soft shifting and the irregularities between 2-3 is a design issue (a flaw but intentional as Mercedes wants smooth and not the abrupt shifts that BMW used to have).
Further reading on performance and reliability between the 722.6 (5-speed) and the 722.9 (7-speed) revealed that over time, the old 5-speed has proven to be an historically industry-wide highly acclaimed unit for it's reliability and longevity. Some mechanics complain about the 722.9's problems, where the 722.6 had so few.
Research on TrueDelta.com for actual repairs on the 722.9 showed some trends. Starting at 70,000 to 200,000 miles many replaced their engine and transmission mounts. Some leaking of ATF into the conductor plate required opening the transmission and replacement, with some taking advantage to replace the valve bodies at the same time. Coolant leaking into the ATF is an issue for some. But overall, only 7% of all W204 repairs were caused by the 722.9 transmission, with expensive repairs (over $1000) representing 20% of transmission repairs, meaning only 1.4% of all the repairs reported to TrueDelta for the W204 were for the transmission and cost over $1000, which is low by any measure.
However the most common "fix" of shifting issues was the update of the TCU software for all 722.9's with MY 2008 thru part of 2011. This seems to solve most or all of the "lag", however does not resolve the "soft" or "2-3 gap" issue. Some 2012 and newer transmission issues were solved by a reflash of the TCU software. Recommended if the transmission is acting funky is to get this done at the dealer, usually for free.
Will I get the valve bodies upgraded (Weistec) or replaced? Only if the 722.9 keeps going into limp mode, which can also happen if an internal gasket develops a leak - this happened on a brand new leased GLC after a few thousand miles, repaired under warranty by a factory German tech and took three weeks. Until then, the W204 is my economy car, and expect to keep it until it is more practical just to summon an autonomous electric taxi, coming sooner that you think.
Keep recalibrating the accelerator pedal to the ECU (some erroneously call this a TCU recalibration, it is not), by switching the ignition ON to it's 2nd detent, pressing the accelerator down HALF way, then turn the ignition off and wait 5 minutes. Did this recently after a year's lapse, and was surprised how much better the 722.9 TCU interacted with the 7 data inputs - the acceleration's change of position being a priority - to determine shift points. Livened up merging on freeway traffic, where accelerator-to-transmission lag is a definite safety issue. Best of success!

Jurgeenh

Interesting, perhaps thats why the dealer keeps saing that is the way this transmission is, by the way my car is a CLS500 2006 so this 722.9 its one of the first models in the market, dealer just replaced my oil and filter and they did not perfom any software update as i know, but stil slipping-flaring about 50-100 rpm on soft acceleration, what i do is just drive the car fast and avoid shift the gears on 2000-1900 rpm using my paddle shifters, and i have more tha 30k miles doing it, that makes me thing that if something were defetive this transmission will be broken long ago, 30k miles that i've driven is a long distance.

Acapulco Bill

The 722.9 in the CLS500 is the higher torque version than used in most W204's (C200, C300, C350). Did you specifically ask the MB dealership to update the software on the TCU?