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R172 Downshifting

1699 Views 9 Replies 7 Participants Last post by  fcch
I'm not an auto tranny person. In fact, this is the first auto I've owned in a very long time. But I loved the SLK350 enough that I went with it anyway.

When I get into it, and I don't mean flooring it, and it downshifts, I'm seeing it go so many gears down that it ends up in a low enough gear that it's already at redline and takes a couple seconds to upshift another gear. Before I take it in to the dealer (it's a CPO), I'd like to hear others experiences. I don't think it's a typical MB behavior as my wife has a C230 and it doesn't do that, and I've had a C300 loaner, and it doesn't do it either.
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are you in C or S mode?
In a 2012, it's E or S, and it doesn't matter. Does it in both modes.
Something is out of adjustment, or in other words it has a mind of its own - assuming that is you are not hitting the kick-down inadvertently. Needs someone to verify and correct.

The SLK will not be at all like the C230, not sure about the C300 though - I have not had any experience with the 300.

In E, the programming of the box will be to get you into a cruising gear as quick as possible, downshifting will be left to the last minute and even then it will only shift down to the next best cruising cog. Unless you kick-down, then the box will go down as far as it needs to give you a clean acceleration.

In S, the programming is totally different - holds gears longer and will often stay in 5 until it knows you are at cruise. It will recognise when you lift off and hit 3 pretty quickly and when you lift off in 3 it will go to 2 without a blink thinking that you are going into a corner and need the lower cog to leap out.

Have your dealer drive it and comment.
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If I do hit the kickdown, would you expect it to go down so many gears that it redlines?
The only way to lower (skip) gears that quickly is to hold the paddle shifter down.
A quick click should shift it one gear at a time.
Even in E mode, my 2014 SLK 350 will hold a gear upon rapid acceleration until it hits the redline. I found this out unintentionally the first time I tried to see how fast it would accelerate, expecting it would shift up and continue to accelerate.

When I test drove a 2015 SLK 350, the salesman told me that the car was set to shift at the redline. I find that hard to believe as at that point, you hit the rev limiter that negatively impacts acceleration.
If I do hit the kickdown, would you expect it to go down so many gears that it redlines?
Kickdown tells the box that you need to get out of something quickly - eg, overtaking, so it will find the best gear to enable the quickest acceleration from the speed you applied the kickdown. The gear it selects may well be a couple of cogs below, but no, it is not going to immediately put you on the red line of the lower gear as it is no point!

You need to have the car looked at, it could well be that your kickdown is so far out of adjustment that you are hitting it prematurely - but whatever it is, you will not fix it here. The car is new to you, again, have it looked at.
The gearbox does learn driving style so if the car has been driven aggressively eg. On test drives then it may have been "trained" to hang onto gears.

Obviously, with an automatic the car will always shift up to protect itself so even if it had been driven aggressively it won't gave damaged anything, the car just needs to be reset to make it drive less like a demented puppy.

I don't know if it's the same on a Mercedes but on VAG cars you can put your foot on the brake then turn the ignition on (but not start the car) and hold your foot on the brake for 1 minute and it will reset the gearbox.

It could be worth a try.
Like jwa96 said, ... try resetting the transmission.

I believe it is the GAS pedal you hold down and not the brake.
On my GLK 250 that's how it worked anyway.

With the car OFF, put the gas pedal to the mat, turn the key to position 2 (not start), ... keep holding the gas pedal down for about 30 seconds, ... turn OFF the key and let off the pedal.

If this doesn't change anything, definitely take the car in to have it checked.

Have fun with your new ride, ... I sure am!!

Happy motoring!!!
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