I’m in the market for a CL550, and I have a question about the way the transmission shifting works. There aren’t any CL’s in the US yet, so, figuring that the CL transmission probably works the same way as the S550 transmission, I’m posting this message to ask S550 owners how their transmission works.

On my SL55, in S or C mode, if the display reads D, and I tap the lever to the left or hit the left paddle, the transmission may or may not downshift, and the display reads 4, meaning that the transmission will shift to no gear higher than fourth.

On my E500, in S or C mode, if the display reads D, and I tap the lever to the left the transmission may will downshift, and the display will read the gear the car is actually in, and from then on the transmission will shift to no gear higher than the number displayed. It seems that the transmission picks the gear to shift to by looking at the actual gear the transmission is in when the lever is pressed to the left, and sets the highest gear to be one lower than that gear.

The net of this is, when you’re going into what you’ve decided is a third-gear corner in the SL55, and the display reads D, you give the left lever of left paddle two taps as you’re braking and before you line up on the apex, so that when you start to put your foot down just before the apex, the transmission is already in third. It doesn’t have to downshift, so it’s easy to apply the power smoothly and controllably. Going into a third-gear corner in the E500, if the display reads D, and I tap the shift lever to the left twice, I may end up in third or I may end up in second. If the transmission doesn’t read the deceleration that precedes the tap as sufficient reason for it to downshift to fourth on its own, I’ll get third. If the transmission does read the deceleration that precedes the tap as sufficient reason for it to downshift to fourth on its own, I’ll get second.

My question to you S550 owners is, “How does the S550 do it?” I realize that the S550 is a seven-speed transmission, not a five-speed, but I suspect that it follows the same principles as either the SL55 or the E500. To test, put the transmission in C or S, and drive down a moderately steep hill at a slow pace so that the transmission will select a gear lower than 7th on its own. Then tap the left shift button once. Does the display read 6, or does it read some lower number? Or does the display work differently on the S550 than either of the cars I have?

Thanks for your help on this.

Jim

 

you have shifters behind the steering wheel, left for downshift right for upshift fairly easy, and addictive!

once you click and hold the left button it will shift to the lowest available gear then you work your way up

 

Yes, both the E500 and the SL55 do the same thing (the SL55 with the lever and the button on the wheel and the E500 with the lever), but I'm not interested in the behavior when you click and hold, but rather the behavior when you just click.

Jim

 

I had the same confusion between an older S55 and newer C55. The behavior is closer than you think on single tap. The confusion arises because, with the older behavior, you often don't know what gear you were in.

You might be cruising in D, thinking you're in 5 but really in 4. A tap will downshift to 3 in the new program, but the older program will display 4 (D-1) while the newer one will display 3 (the actual gear you're in). Of course, then you the have different max-gear settings. Hold-one-second is the way to select "best-gear" (multiple downshift) with either program.

I suspect the new behavior is the same for the 7-speed.

http://www.billsden.org/mercedes/slk...b_27_60_44.pdf

 

Precisely.

I do too, but I'd like to confirm it. This is a deal-killer for me, if our suspicions are correct. It means you can't reliably select, say, third gear for a third-gear corner.

Jim

 

Are you saying that, with the newer AMG cars, you can't predict what gear you're going to be in? I'm surprised that AMG would do that to their customers, who presumably have sporting sensibilities.

Jim

 

Exactly. That was my original complaint. If you're at a stop sign in D, a tap puts you in 1. If you're light-throttle in fifth, a tap puts you in 4. If you're in a passing or mid-speed application, you can be in third of fourth, in which case a tap will put you in 2 or 3. The good news is that, unlike the old program, the cluster display shows what gear you were put in. The bad news is that you have to look down to see what gear you're now in.

Apparently, enough people complained that this warranted a bulletin (the one I referenced earlier).

With the older program, I know that three taps from D and I'm in second. In a sense, it's better control of the transmission. But with a 7-speed, I suspect this would be impractical. Five taps to second is a bit much to keep track of. The philosophy of the new program is that you're probably already closer to second than top gear, so the computer can be a bit more involved in the decision. I'm pretty sure this makes perfect sense in the 7-speed.

 

PS. Although I hated the new program when I first got the car, I'm very comfortable with it now. I drive both the older S55 and my wife's new C55 regularly and now prefer the new program. If you're in fifth, e.g., a little throttle as you tap the button gets you to third (the throttle tells the TCU "fourth" and the tap "one more.") It's uncanny how often it picks the gear you want. If you want to be a bit more aggressive, one more tap and you're there. It's as fast as you can expect from an automatic.

My biggest issue is that when I haven't driven it for a week or so my wife's adaptations have made the transmission wussy. But the reset trick fixes that quickly.

I suggest you drive one before deciding that this transmission program is a problem.

 

I have experience with six-speed transmissions in BMWs and five-speeds in MBs. I can see that there's more to keep track of in a seven-speed than a five-speed. OTOH, there's no time going in to a corner to see what gear you actually got.

If you get a gear higher than you want, the transmission is going to downshift when you put your foot in it. Assuming that you're dialing on the power more and more as you pass the apex and unwind the wheel, the transmission could actually downshift after the apex, which is certainly not something that you want, since it would put a gap in the application of power, that would unsettle the car at a point in the corner where there's a high g-load.

If you try to outsmart the transmission and fail, getting a gear lower than you want, you're going to run out of revs and have to shift too early in the corner, and you'll also have more rear-wheel torque than you expect, so application of the throttle is more likely to break the rear end loose or have the traction control intervene, if you haven't turned it "off" (I assume it's never really off like the other MBs).

I do a lot of driving on twisty roads I know very well, and I have a clear idea of what gear I want to be in when. I will follow your suggestion and try it, but I'm not optimistic.

Jim

 

There's also always M mode.

 

Yes there is. I find M-mode maddening. There's the delay between pressing the button and having the transmission shift that's not so critical for downshifts, where you just have to have the shift take place sometime around turn-in, but really critical for upshifts, where want to wind it out, but don't want to run into the rev limiter. The car is perfectly competant to figure out when to upshift, but it doesn't know where the corner is or how fast a corner it is, so it doesn't know when to downshift, or what gear to down shift to.

Take a look at this thread: https://mbworld.org/forums/sl55-amg-sl63-amg-sl65-amg-r230/158933-shifting-sl55.html

Thanks,

Jim

 

I find the delay reasonable (for an automatic) and predictable. There's nothing like a stick, of course, but I wonder if either Speed Shift has been improved recently or whether yours is not quite right. You might want to test-drive a new SL55 or other model as a control. It's certainly possible that we just have different expectations from this automatic, but I'm a pretty aggressive driver and find the '06 AMG manumatic gives me sufficient control.

 

Thanks, I'll check it out.

Jim

 

I just visited the dealer and found out that there's no M mode on the S550, and, presumably, on the CL550.

Jim