jkowtko

I tried comfort mode as well. In my car it still seems to take off in first gear, although the shift points are lower. It felt like the problem was reduced when in comfort mode. I can try this again tomorrow morning.

Does the ECU control throttle body movement differently when in Comfort mode, and during gear changes and lockup?

Glyn M Ruck

No ECU does the same in Comfort. TCU changes up earlier. The only time the car should pull away in first in C mode is if you apply over 75% throttle. (Does not apply to high torque diesels)

Kropf

The best answer I have seen to this problem is explained in an article I first saw in Transmission Digest May 2010 pg 38-40 titled:
Mercedes 722.6: Cold Stall/TCC Shudder
and is currently available online at:
http://www.sonnax.com/publications/c...shudder-part-i
http://www.sonnax.com/publications/c...shudder-part-2

The following document may also be found helpful:
http://www.sonnax.com/system/pdfs/93...RA-2010-BW.pdf

Carsy

Wow !, An interesting read. Thankyou.

jkowtko

Okay I was able to reproduce a little better ... I think what seemed like 1st gear in Comfort mode was actually the rpm flare, and the TCC lockup felt like a 1st->2nd gear change.

So I am comfortable saying that the problem is engine rpm flare in the starting gear (1st in S, 2nd in C), due to what feels like the TCC clutch being slow to engage and tighten.

The equivalent in a manual transmission would be letting the clutch out too slowly, and then popping it when it's only halfway engaged.

This only happens for the first minute or two after a cold start when the trans fluid is cold. It also only happens when I drop from 3rd or 4th gear down to a stop, and then accelerate quickly from the stop without giving the transmission time to do whatever it has to do to prepare for acceleration. If I wait a couple of seconds at the stop (e.g. to let cross-traffic pass) the problem does not occur.

After two minutes the engine warms up and the symptoms go away entirely.

Thanks for the article references, Kropf -- it's always interesting to see the discovery and resolution process. As a mechanical engineer I can appreciate the complexity of an automatic transmission -- no envy for the guys that had to design it, and not surprised that evasive problems like this occur. This is really engineering at its best

Unfortunately I think the issues that I am seeing are somewhat opposite of the symptoms identified in the article. The article speaks of shudder/stall when cold, and rpm flare when warm. My car is seeing rpm flare when cold, and I do get some momentary idle shudder but only when warm.

Ugh ... maybe I should try to find a local 722.6 expert who is up to the challenge of troubleshooting this one.

sammydragon3

im in the same boat as u on this ....happends to me depending on how easy i am on the gas

only thing to can do is check all the values on SDS, check TCU, and valve body and hope

i already had a trans drain at 35k and 70k miles

indymerc

just chucking it out there....check your battery on a proper battery tester,incorrect/low voltage can cause various problems with etc from cold.once the car has been running for few minutes(enough time for alternator to charge) the gearbox works ok.
come across this a few times.

jkowtko

Good idea ... that's something I thought about way back when this first started, but I got sidetracked with throttle body cleaning, etc. The battery is still the original, 8 years old now. Starting has never been an issue but will do a load test and see if it's time for a replacement.

Thanks. John

jtwillia2

You may have already done so, but remove and completely clean your throttle body, including the internals and the back side of the flap that faces the rear of the car (see my thread here) - mine had a load of gunk and oil buildup on and around the back side of the flap - this one thing fixed and smoothed out my rough idle, 'difficult' starting, weird shifting, etc.

jkowtko

Yeah, that was one of the first things I did a few months back. It was reasonably dirty, had residue around the tunnel where the flap rests closed, and cleaning it probably helped a bit, but not much. I am still toying with the idea of replacing the throttle body, but don't want to drop $500 quite just yet.

Anyone have an M271 in the Bay Area that wouldn't mind me borrowing your engine parts for an hour or two?

jtwillia2

Did you remove the plastic cover that houses the electrical stuff, plastic gears, copper connectors, and carbon tracks, and clean those? Mine had some buildup in there too.

jkowtko

Yep, did that too. sprayed it with deoxit and rubbed it a bit with a cloth. But I didn't really notice any buildup to begin with and didn't want to damage anything so I was pretty gentle. I put a tiny bit of silicon grease on the gears to keep them lubricated.

The car feels great at all speeds, acceleration, downshift, etc. It's just at the idle speeds and at the stop where I have the issues. From what I understand of the transmission it sounds more like the TCC is a bit slow to fully disengage when coming to a complete stop.

In order to check the throttle body further I thought about hooking up my ODC-2 reader to monitor throttle position during these idle drops.

indymerc

Have you checked for split breather hose under the air filter housing?i find that these are more noticeable when the engine is cold as the adapted values are way out.
Possibly getting of track though as it sounds more transmission fault.

jkowtko

That was a recall item the dealership did back in late 2008 ... they referenced part #271-010-00-82-05, which is the complete hose/check-valve/clamp/gasket set.

I have not had a CEL since then, so I'm assuming the vacuum hoses are not a problem.

ghaun

jkowtko,

I believe that I have a very similar issue and was wondering if you have found resolution or if I can help with further data points.

I have an R230 (SL600) with the 722.6, which has the same lurch that you are referencing. Mine does not completely go away as it warms, but lessens in severity.

As I pull away from a stop, I notice the rpm increases slowly as if there is significanat load and then there is a snap as if a clutch was dumped abruptly. I have verified that this happens in 1st gear and is absolutely not the 1st-2nd shift. I have hooked up my STAR system to verify gear position. I need to get more familiar on this system to look at other tell-tale signs.

If I pull away fast from a stop, then this condition does not occur. As I am learning more of this system, I am leaning toward a TCC lock-up problem. It seems as though there is partial slipping from a stop, which would create the added feel of load and then the jerk/lurch is a sudden lock-up.

I still need more data points and would love to know what you have learned. I too read the cold stall issue and believe that this is related. Others have said to replace the TCC solenoid. I need more research.

Let me know what you have found.

BTW, this issue came about abruptly. Subsequently, I also noticed trans fluid leaking under the car and found the trans connector leaking. Trans fluid had found its way up to the TCM. I had a TCM tune and all was verified fine with the TCM. I changed the fluid and did a complete flush as well. I'm wondering could the fluid have also worked back up into the solenoid connector via the internal o-ring and caused partial damage to the pwm-controlled solenoid.

Thanks,

Greg

jkowtko

Hi Greg,

As of late I've been busy with other matters (stereo upgrade in progress so I haven't probed more into this issue.

Since my problem only occurs on cold starts I'm just taking the extra time to pause at the first few stops for the transmission to catch it's breath for the acceleration, until it warms up a bit and the problem goes away.

However I have been noticing the momentary idle drop a bit more now ... that generally happens when the engine is warm. Seems like the tranny waits a bit too long to disengage when I come to a drop, and it pulls the idle down a bit int the rough. This may be related to the same issue ... or maybe it's time for a new throttle body ...?

ghaun

Sorry for not addressing you with your first name. Not sure

Anyway, I have though about this a bit more and it seems as though, once pressing the throttle the torque converter is trying to perform torque-multiplication as it should; though, the clutch is partially engaging causing the perceived drag...up until the head-jerking snap occurs (which I believe is lockup). During this snap around 2000 rpm previous to the 1-2 shift, the rpm behave as though a manual clutch is dumped without matched rpm (thus torque multiplication is still there to some extent).

Are you referring to the idle drop when stopping, almost like a manual clutch is engaged too long while stopping, but released prior to stalling.

Do you notice a very engaged deccelreation, as if one is using a manual gearbox for engine braking. As I come to a stop, I feel each gear and have the burble during decel. I really like this, but don't know if this is by design.

I'm not sure that I notice the rpm drop and recovery at idle, as you mention. I will have to give this a try.

I'm thinking of trying to get a discussion with the sonnax folks.

Let me know your thoughts.

jkowtko

Greg,

Everything you mention sounds familiar to me ... overall it feels like the clutch is not engaging/disengaging in a timely manner ... but only in specific scenarios.

If you want to try to talk to Sonnex, yes I would be interested in joining you. I have a Mech E background so I should be able to understand whatever they tell us ...

Thanks. John

VVF

When did you check your alternator pulley last time?
It should spin freely in one direction and engage the alternator in the other direction.

I am not quite sure, but I had similar shudder when coming to a stop at a red light etc. Alternator pulley has seized (did not spin freely, always engaged the alternator). After replacing the alt, I think I have not felt the shudder so far...

jkowtko

Good suggestion. I haven't noticed the idle drop lately as i've been busy cranking up my new stereo speakers and amp ... but I'd like to go back to the pulley and accessories at some point (including battery test) to see if there is any unnecessary drag on the engine.

jkowtko

*** update ***

It is now four months later, and I can say that the problem is 95% gone now ... so effectively it feels like it's operating normally. Seems like whatever gunk was making the valves stick has worked itself free with the clean fluid.

This makes me a FIRM believer in keeping fresh fluids in the car if you want to avoid costly repairs. A simple thing as a sticking valve can make it look like your transmission has gone out, prompting a full replacement that may not have been necessary. If keeping the fluids fresh will avoid most of these problems and allow your transmission to live it's full and normal life, then I think the cost of the maintenance, even at shorter than prescribed intervals, is well worth it.

Carsy

John,

Interested to know the transmission oil change history of your car ?.

My MB mechanic suggested draining the fluid every 50,000 km. (Flush only fluid is dark.)

jkowtko

I have to say I wasn't very good about it when I was paying for service ... have done much better since I started DIYing --

* the leaky adapter plug was replaced under warranty, sometime under 50k miles. I don't know if a drain-and-fill was done at this time ... I think it was just topped off to replace the lost fluid.

* drain-and-fill with pan gasket and filter change, at 57k miles. 6 quarts charged on my bill.

* after that, nothing until my DIY full flush at 95k miles.

Shifting was getting sluggish, especially downshifting on the highway. And the transmission noise was becoming audible. The full flush made a very noticable difference.

The general recommendations recognized by this forum are to do full flushes with filter changes and maybe adapter plug changes as well, every 60k kilometers or 40k miles. I will probably do it every two years (~20-25k miles) after seeing the difference that it made in my car. I may not pull the pan and change the filter on these interim changes, but I will drain the oil in the pan through the plug and then flush though the cooler lines. Without pulling the pan this can be a 15 minute operation!

awesomeBLT

I have a 722.6 transmission and noticed the slipping and erratic shifting after 40K miles from the last flush, oil and filter change. That's my Q that its time to do it again. Drained and dropped the pan, cleaned the magnet, changed the filter, replaced the pan. The oil still looked pretty clean as did the magnet so I'm assuming it was the filter getting clogged and restricting flow. Removed the oil cooler return line from the passengers side, put 5 quarts of Shell ATP 134 in started the engine and pumped out 3 quarts (oil cleaned up nicely). Re attached the oil line, put in 3 more quarts. Drove it around, oil checked OK. All problems solved. I think most problems are associated with the filter getting clogged usually after about 40K miles. Be sure and do the flush by removing the return cooler line from the passenger side and running 3 quarts into a container as that flushes out the torque converter and the cooler. If you are still having the same problem try draining out a quart from the pan and adding a quart of Lucas Automatic transmission additive. Sometimes you have a sticky spool valve and this stuff seems to make things work smoother. Only used it once problem solved.

jkowtko

Okay, after a couple more months I guess the problem isn't completely gone ... I can still feel the hesitation of TCC lockup when cold. Also when the engine is warm, TCC release seems delayed when coming to a stop.

I'll see if I can find a local shop to do a Star test.

Glyn, do you support the idea of adding Lucas transmission additive to try to free the sticking valve?

Thanks. John