The transmission control in my new '06 C55 seems at odds with the book, but the Saturday on-call service advisor says it's working as designed. I'm not ready to believe him yet.

I expected a single pull of the shift lever to D- (or tap on the - paddle) to consistently drop one gear. This is what my '01 S55 does and what the C55 manual documents. But it drops several gears, as it thinks appropriate. At idle it locks into 1, at 20MPH to 2, etc. It looks like it's acting as if I've held the shift lever for a few seconds, but it's what happens on a quick pull. This is in C or S modes.

Is this mind-of-its own behavior something normal, or should I be able to downshift n gears with n taps like I'm used to? Thanks in advance.

Martin

 

seems normal to me. But for me, if im actually using the shifting, i use the "M" mode. I feel it's alittle bit more crisp as to the shifting.

 

In C or S modes, it will do what it thinks is best to a certain degree. More in C than in S. In M, it's all up to you. So, if you want n shifts for n pulls, use M. Damn with the letters.

As a test, put the car in C, click the paddles to put you in D at low speeds, and floor it. The car will downshift even though you are in "manual" mode.

Cheers,

JPOG

 

The service advisor is right. Although I'm unsure of the year, I believe it's 2005, AMG Speedshift transmission logic is 'one touch' downshift. No matter in C, S or M using either the wheel buttons or gear shift lever to downshift requires one touch to select the proper lower gear.

If you downshift early, you may get sequential downshifts. Downshift late, say, at the end of hard braking, and you'll most likely skip some gears.

It takes some getting used to, but it's great logic. You can concentrate on your approach and braking, click once and know you're in the right gear for the exit. Brakes are the best for slowing down, downshifting upsets the car, hammer the brakes, click once just before brakes off or trail braking to turn in, accelerate out.

Plus, the trans is truly skipping gears for you, so the downshift is much quicker. Great stuff.

I'm not sure that I am understanding what jpog is describing, but when you are in S or C, you are not in "manual" mode. C and S modes will upshift automatically at or near redline if set at 1, and will upshift normally gear to gear automatically if set at 2 through D. When in M mode, no upshift unless you do it. The engine will just bounce of the rev limiter endlessly and wreak havoc with your motor. Downshifting will take place in all three settings either by pushing the gas pedal to the floor (C and S) or simply coming to a stop (C, S or M). I may be wrong on this one, so someone should confirm as I won't be driving my C55 for a few weeks, but I believe the indent or notch in the thottle when depressed fully (past the initial stop) will downshift the car when in M mode.

With the old logic, the steering buttons only worked in M mode. With the new logic, like in your 06 C55, the steering buttons work in all modes (C, S or M).

 

Thanks, kjb55. It's particularly frustrating now because multi-gear downshifts during the break-in period aren't a good idea. Hopefully when I can start driving the car with a bit more spirit I'll learn to appreciate the logic.

It will take some getting used to. The nice thing about the older behavior is that you don't need to glance down at the cluster to know what gear you're in. I'm very used to three quick flicks to second, and wish I can select that. Going M seems like overkill for most situations of commuting or moderately recreational driving with the occasional adrenaline cloverleaf.

Martin

 

All C, S and M Mode will automatically downshift if the car speed ( = rpm dropping ) slows down. The 'auto downshift' behavior differences between C/S and M are follows:

1. In C/S mode, you will not read gear change information from the console. In M mode , you will.
2. In C/S mode, auto downshift is much smoother, almost jerkless. However, in M mode, the auto downshift from 3 to 2 is jerking badly.
3. In M Mode,
at speed < ~65km , auto-downshift occurs from 5th to 4th
at speed < ~50km , auto-downshift occurs from 4th to 3rd
at speed < ~40km , auto-downshift occurs from 4th to 3rd
at still , auto-downshift to 1st.

So if you manual down shift at the same times at various points where the autotran is doing auto downshift, you might experience difference results.

 

I have a 2005 C55 and what you describe does NOT happen in my car. In S or C mode, the touchshift feature works just like my old 2002 C240. With a fast tap of the shift lever (or shift buttons), the car will upshift or downshift ONE gear at a time. If I HOLD the downshift lever (or downshift button) for a second or two, then it will go into the optimal gear for best acceleration. If I HOLD the upshift lever (or upshift button) for a second or two, then it will go back into standard automatic mode.

Unless this was changed for 2006, what you describe doesn't fit.

 

Hello PC... what is the build date of your car? Mine is 09/2004, and functions different than yours (same as Whoover) and the complete opposite of my 2003 C240.

Thanks.

 

I can't remember off the top of my head now. But I do know that I ordered the car in Feb. 2005 from the factory (I did not buy from existing dealer stock). I took delivery in May 2005, so the build date was sometime between those two dates (closer to May 2005).

In other words, I'm pretty sure my build date is later than yours.

 

The dealer's tranny specialist confirmed that the "one touch" behavior is what it's supposed to be doing. This means the TCM decides the gear. He implied it was a change for '06, which doesn't explain why some '05s work this way, but other work a gear-at-a-time. It also doesn't explain why the manual wasn't changed.

As Mercedes moves to standardize on the 7-speed, I guess this change is inevitable. Downshifting from D to 3 with our 5-speeds is not so bad a gear at a time, but with a 7-speed I can see it getting harder to keep things straight during offramp maneuvers and the like. It makes sense that AMG would want to introduce the notion of TCM-mediated downshifts sooner rather than later.

I'll reserve judgement on how I like it until the break-in period is over and I can drive the car a bit harder.

Martin

 

My regular service advisor (without my even asking, I might add) has gotten some additional info on the transmission program. The factory confirms that, depending on build date, '06 C55s were delivered with either the one-gear-at-a-time downshift or the mommy-picks-the-gear program.

He also added that the software upgrade to mommy may be applied (either pre-delivery or during service) to any C55, as there are no hardware differences. Some dealers are more aggressive than others in applying upgrades, which would explain an '05 with the new program.

BTW, I'm a lot more positive about the new program now. Once you get a little experience with the tranny you find the selected gear to be pretty predictable. The biggest problem has been dueling adaptations. The car is my wife's and when I take it for a day it takes a while for the car to get whipped back into shape.

Martin

 

Thanks for the info. My question is this: Is the software "upgrade" to the "mommy picks the gear" feature suggested by Mercedes Benz as something to do at my next service? Is this just a voluntary thing on my part, or is there a "bulletin" that all C55's should have this softward upgrade?

 

I asked the service advisor and he said it's up to the dealership. Typically, the transmission software upgrade would happen if any other work is done on the transmission, but the dealer apparently has the discretion to just do it. I'd talk to your dealer if you're interested.

Martin