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Discussion Starter #1
Hi guys,

I recently purchased a 2007 C230 Sport sedan with 110k miles and have noticed a slight problem with the shifting pattern in the automatic transmission.

Here is the problem:

From stop, I've had no problem getting into 1st gear with a shift around 2500 RPM. In 2nd gear at around 2500 RPM the transmission quickly shifts so that the engine races a bit and the RPMs go from 2500 to 3200 RPM in the matter of a half a second. It almost sounds like the transmission quickly downshifts into 1st and then quickly shifts into 3rd. I've had no problems with hard shifting or grinding of gears. And the problem is more pronounced as you step on the accelerator aggressively.

I took my vehicle to the dealer and was able to replicate the problem with the technician. Since the vehicle had been serviced at this dealer, the service consultant told me that the transmission fluid and filter had been changed only 2,000 miles ago before being sent to auction. They told me that they could not find any error codes in the onboard computer and that there were no additional software updates. They finally recommended that I continue to drive the car as normal and the problem may or may not get worse.

Have any of you experienced a shifting problem like this? I believe that the problem is not with the transmission but rather with the onboard computer (transmission contrul unit - TCU). I spoke with MB Customer Service and they have not heard of a problem like this nor do they have any service bulletins regarding this issue.

Can anyone shed light on this situation? Is the problem simply a bad TCU or a programming issue or is it something more serious like a bad transmission?

Thanks!
 

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i dont know if this ecu reset works on your car but

turn the key to position 2 in which all lights on the cluster light on

press the gas all the down until u push the button with your foot....hold the button down for 6 seconds

then your foot holding down the button turn the key to postion 1 where only the battery stuff is on

then drive your car hard a bit....if will cause the trans to hold the gear much long and feel like new
 

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Discussion Starter #4
Thanks for the info! I will try to reset the ECU using the technique you've described.

I asked the dealer if the technician noted anything ususual about the transmission flush and fill on the service report and he said there was nothing noted. He did mention, however, that the technician added a special MB fluid in the transmission fluid to aid in smoother shifting. I don't know what that is but it sounds like the previous owner complained of a similar problem.
 

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Discussion Starter #5
After some more thought, I believe my tranmission is slipping at the top end of 2nd gear - from 2500 RPM to 3000 RPM. But how does this happen???

Did the previous owner in some way abuse the transmission by running it too hard or is it a manufacturer's defect? Can someone school me?
 

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did they "flush" the system ?

or drop the pan and drain the fluid out?

i heard on here flushing the system might cause problems
 

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did they "flush" the system ?

or drop the pan and drain the fluid out?

i heard on here flushing the system might cause problems
Yes, the 722.9 (7Gtronic) transmission should have a simple drain, filer replacement and refill, which will only change about 1/3 of the total fluid capacity. This is prescribed at 39K miles. MBZ will deny any warranty claims if the transmission fails and this service was not performed this exact way.
 

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Discussion Starter #8
I'm not sure if they did a complete flush or simply a drain, filter & fill.

The service advisor did say that they added a special MB fluid which helps the transmission perform better. I guess the prior owner complained that the transmission was slipping a bit?
 

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If the service was performed by an authorized dealer, then I would not worry about that being the issue as they would have used approved fluids and procedures. You could just have a minor problem that's going to manifest itself with this slippage feeling, or it could be something major. I'd pull codes on the transmission to see if anything is going on there. If not, then keep driving it until the symptoms change. The 7Gtronic has some peculiar properties that have caused a lot of customer complaints, but in the end, 99.9% are just normal operation.
 

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Discussion Starter #10
Here's the latest. I got fed up with the poor shifting and RPM acceleration between 3rd and 4th gear so I took it back to the MB dealer for another evaluation.

This time they found the problem! They hooked up the transmission hydraulics to a monitor and found that the hydraulic pump assembly was going bad. The service guy recommended that while they are repairing the pump assembly that they might as well put in a rebuilt transmission for $500 more.

The service guy told me that MB model years 2003-2006 had the 722.6 transmission package which called for transmission oil change at 100,000 miles. My model (beginning in model year 2007) has a different transmission package (722.9) which calls for a transmission oil change every 40,000 miles. Guess what? The first transmission service on MY vehicle was done by the original owner at 100,000 miles. It should be no surprise that the transmission is now fried! And since I bought the car from a wholesaler, I am left holding a $4200 loss for a new transmission and pump assembly!

Maybe it's time to get out of this car all together? I can't sell my car in all honesty with this problem. I'm working with the dealer for them to buy my car, fix the transmission at their cost and sell it to someone else for a profit. That means that I will be taking it up the <you know what>!

Comments / Suggestions?
 

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Here's the scoop...

The 722.6 transmission was sold as "sealed for life - no service needed". It came with a filler/dipstick tube, but no dipstick - just a tamper-evident cap for MB workshop use only. They started having an increased failure rate beyond 100K miles, so unofficially, MBZ suggested a 100K mile fluid and filter change. The problem is, they deleted the torque converter drain around 2001, so dropping the pan would drain out less than half of the fluid. This is better than nothing, but still not a real fluid change. Some indy shops actually figured out how to disconnect a cooling line and do a pump-through flush, but some of those shops also got lazy and did just a flush, with no fluid change.

When the 722.9 came out in 2004 (for some MY2005 vehicles, mainly v8s) they at first still sold it as sealed for life. In fact, it doesn't even have a filler tube, it can only be filled through the drain plug via a fluid pump and the level checked via an overflow tube. Someone eventually realized that the 722.6 and 722.9 are not really very different (just in gear count) so there is no more reason for the 722.9 to be sealed for life than the 722.6. Plus, they started having hydraulic pump failures, so they decided that it really should have a fluid and filter change at around 60K km, i.e. 39K miles. But they only recommend one change at 39K for a break-in period. The good news is they added back the torque converter drain so you can actually get all the old fluid out.

These transmissions work very hard and generate a lot of particulate, just like an engine. I changed the fluid in my CLK550's 722.9 at ~39K miles and it was absolutely black. The magnets in the pan were twice their size with collected particulate. After seeing this, I am now evangelical about changing fluid every 40K miles. Actually, I think I'd recommend it every 30K.

The job on the 722.6 is fairly easy as it requires no special tools and can be filled from the top and level checked via a dipstick (you can buy one, or build a bootleg version with instructions found here on the forum). The 722.9 is a bit more difficult because you need a pump ($200) and you have to be able to lift the car enough to work underneath and keep it level, with the engine running. I can do this in my garage with four jack stands. The actual parts (oil, filter, and one-time use bolts) for the change will run about $100. The dealers charge around $400 for the service.

The early (MY2005/MY2006) 722.9's were prone to pump failure. Speculation is that it's caused by parts from a failed bearing/bushing contaminating the pump. Unfortunately, it's a defect and MBZ is not always good about covering things like that outside of warranty unless it's "just" out of warranty. Frequent fluid changes can help with this by keeping all of that particulate out of the pump.
 

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Discussion Starter #12
Thanks for the info, Rodney!

After speaking with my MB dealer, they are not interested in purchasing my vehicle. It's going to be hard to swallow a $4,000 transmission and hydraulic pump assembly bill so I am speaking with an independent transmssion service company.

Am I making a wise decision to have an indy do the work instead of the MB dealer? The indy says that he's done a lot of MB cars and I assume he has all the tools and knowledge necessary to get the job done.
 

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A reputable indy with MBZ experience, yes that's a good decision. Mr. Transmission? NO!
 
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