Hey, I'm new to the form and looking for some advice. I'm a college student and have always loved the w209 chassis. I was looking at clk55s but the clk550 better fits what I'm looking for. I am looking at a 2007 clk550 with 127000 miles. The car looks well maintained (my mechanic will double check) but should I be looking for something with lower miles? Any input would be appreciated

 

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You need to check that the engine is beyond the range for potential timing chain idler sprocket failure. Get the VIN and then use this site to find the engine serial number:

https://www.datamb.com/

It will be in the format of "272xxx 3x xxxxxx". Make sure it is beyond "30 088611" for the V8, or, if you consider a V6 CLK350, then "30 468993". If not, then there is the potential for a very expensive failure. Search the forums for "balance shaft" and read all about it. Note that high mileage is also no guarantee that it won't fail. Some failed at 25K, others at 125K, or even at 200K.

Another thing to consider is that the transmissions up to MY2008/2009 tend to need more attention. Almost all will experience bad speed sensors that require a $1500 visit to the dealer. Also, the fluid needs to be changed every 40K miles and it's not a DIY unless you can safely lift the car to work underneath and while keeping the transmission pan level.

Furthermore, since you are a college student, i assume you do not have the ability to DIY (garage, tools, etc.), and also you might be on a tight budget and not have thousands of extra dollars banked to pay for repairs. While owning a MBZ can be very satisfying, and buying a used one can save tens of thousands of dollars, keeping them properly maintained and addressing any "problems" can become expensive. There is an old saying that goes, "There's nothing more expensive to own than a cheap Mercedes-Benz."

 

​​​​​​The service costs won't be an issue for me. I'd rather pay for a quality car then anything else. And I'm used to working on my current Mercedes. I checked the VIN and it's past the balance shaft range. Thanks for the response

 

What about 2006 CLK500 ? also same 7 speed tranny 722.9 right ? how reliable a 06 CLK500 ? Thanks !

 

The 722.9 transmission was introduced to the CLK for MY2005 in the CLK500. The MY2005 CLK320 still had the 722.6 5-speed. Then, for MY2006, the M112 (CLK320) and M113 (CLK500) engines were rpelaced by the M272 (CLK350) and M273 (CLK550) and the 722.6 transmission was dropped so both the CLK350 and CLK550 had the 722.9.

 

I say jump on it They are great cars and fun to drive.

 

 

Hi Rudeney,
Could you tell us more about the speed sensors issue? Is it something bad for the engine, or bad as in 'you'll get a ticket' because of high speed?
I suppose some features are triggered by speed, such as steering assistance, break assist maybe? I'm no specialist far from that, but any info on what do these sensors do would be great. I never heard of this being a common issue before, is that a common thuth for clk's ?
Thanks.

 

The speed sensors I mentioned as being problematic are in the transmission. They report the rotational speed of certain gear assemblies in the transmission so the TCU can verify that the shift changes that it demanded have actually occurred. When these fail, the transmission will go into "limp mode" which will disable the torque converter lockup function and hold it in 2nd or 3rd gear. You can drive the car, but it won't be fun. The solution is to replace the conductor plate inside the transmission. On the 722.6 5-speed, that's fairly trivial (drop the pan, drop the valve body with the conductor plate attached, and replace the plate). On the 722.9, 7-speed it's the same procedure, except that the TCU is built into the conductor plate which makes it that part more expensive. But even worse, it requires SCN coding, which can only be done by the dealer. Not even those of us with our own SDS can do that because it requires a licensed SDS with a live connection to MBZ corporate so it can download the encrypted code.

 

How often does this happen? My clk550 is a 2007 123000 miles..so I guess I'm in the red zone...
If I understood you well it would then not go over 2nd or 3rd gear? Or did you mean it would stay locked on 2nd or on 3rd and drive only at that? I can imagine being able to go to the shop on a 3rd, barely... but in second?!...argffffff... I would get beaten up in L.A.!

 

Think it's possible or charlatans?
http://www.ecutesting.com/mercedes/7g-tronic-problems.html
Give your thoughts pls

 

Does limp mode let you drive manual? Ie let you change shift manually?

 

The 722.6 will lock in 2nd gear, the 722.9 in 3rd gear for limp mode. It will stay in that gear - you cannot shift manually. Shutting down and restarting the engine may clear limp mode, but it will come back until the problem is resolved. My CLK550 started doing this and eventually it got so bad that it would not shift into gear from P or N until the transmission was fully warmed up. All early 722.9's will likely fail. The conductor plate was revised sometime around MY2008 and then it was fine.

As for that link, there are some companies that do this repair. What they do is take your ECU out of your faulty conductor plate and transplant it into a new one. I have heard of one forum member doing this with success, but I have also heard of another who had an earlier model 722.9 and those require a new valve body as the revised conductor plate will not work with the older style valve bodies.

 

Hello,
I have a question that I hope isn't too stupid. On my clk550 automatic transmission, as on a lot of automatics, one can change the max gear by shifting the stick. Is that bad to use manual shifting of max gear to mimic a manual transmission drive style? Using this feature can help push the rev instead of letting the shifting automatically engage to higher or lower.
Using it like a manual transmission, also gives engine breaking help.
Is it bad to do that for the transmission or the engine itself?
I hope my question won't make anybody shake their heads. I don't know much in mechanic but I'm leaning..
Thank you so much.

 

I don't believe that it is. The gearbox will only act on the motion if it's allowable. You can shift gears sequentially or, by holding the stick to the left/right you can force the gearbox to drop or raise to the max/min allowable gear for your road speed. Although sometimes you can do this, and throw the engine speed very close to the redline, which isn't particularly comfortable.

​I can't imagine that shifting so aggressively is particularly good for the box, however generally since its a fluid coupling between gearbox and engine output, I believe the change will be somewhat dampened.
I quite regularly use my tiptronic, mostly for upshifting early, or for hill descent/overtaking.

 

Ben is correct - the transmission is designed for this. Keep in mind that doing this only "requests" a shift or gear hold, it does not "demand" it. The TCU will not let you downshift to a gear that would cause the engine to rev over its redline, nor will it let you hold a gear past redline (in that case, it will automatically upshift). The shifts are fairly slow, so it's is not like driving a true automated-manual transmission.

Note that the gear number shown on the instrument cluster MFD is not the current gear, but the "maximum gear requested". What this means is that the MFD can show "3" but you might be in any gear up to 3rd. If you hit redline in 3rd, it will upshift to 4th and the MFD will then show 4th. You might also find that when you need a quick burst of speed with a kick-down, if you slam the throttle and at the same time double-tap the TouchShift to the left, you will quickly get the lowest possible gear, which may not happen just using the throttle alone.

 

I drive this way near all the time. About the only times I am in "D" is when on the open highway. Driving this way all the time takes a toll on the engine. I have to add a quart of oil every 4-5K miles (depending on how aggressively I drive it). I've had the tranny (including the torque converter) fluid changed twice I have not had any transmission failures or issues.

I've been working on an exhaust product for over 3 years and do the testing in the drone ranges, so I drive at 1975 RPM and 2500 RPM most of the time. And I was manually shifting the gears since about 5K miles but probably didn't rev it as high as I routinely do now.

I bought the car new in Oct 2007. It has near 168K miles. The wear on the engine is probably about what it would have gotten to at 250K with "normal" driving. In regular driving, in "C" mode, the tranny always shifts in the 1500 to 1600 RPM range.

There were some boxes unchecked from my teenage years; I am trying to take care of those now.....

 

2007-2009 CLK550 is getting harder to find. Best to find a clean one and jump on it then.