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Auto downshift in manual mode

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Auto downshift in manual mode

 
Old 05-02-2019, 12:45 AM
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Auto downshift in manual mode

Hi all, new member here.

I have something to discuss and get people's thoughts on.

I've found that the downshifting in S and S+ to be too aggressive, ie the revs are way too low when downshifting, which results in jerky engine braking which is not only uncomfortable but also can't be good for the transmission.

I've found a workaround by driving in manual mode, but relying on the auto downshifting when I brake. I've found that the downshift now happens later on, and is much smoother.

My questions are - Does this approach have mechanical sympathy, and Do you do this too?

Thanks
Jack
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Old 05-02-2019, 09:17 AM
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2012 P31 Coupe
Originally Posted by V8Thunder View Post
Hi all, new member here.

I have something to discuss and get people's thoughts on.

I've found that the downshifting in S and S+ to be too aggressive, ie the revs are way too low when downshifting, which results in jerky engine braking which is not only uncomfortable but also can't be good for the transmission.

I've found a workaround by driving in manual mode, but relying on the auto downshifting when I brake. I've found that the downshift now happens later on, and is much smoother.

My questions are - Does this approach have mechanical sympathy, and Do you do this too?

Thanks
Jack
I believe the main concern is the vacuum created by engine braking. It will suck oil out of the engine. Not good for piston/cylinder seal.

Engine braking in itself isnt bad on the ransmission. It uses the "other" side of the gears that we never use when driving forward (only used in reverse)

Would love to hear more answers on this
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Old 06-18-2019, 06:51 PM
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SL 550
I just had the dealer replace the the Passenger side SAM and I am glad I did that because the module requires coding. After it was replaced it unmasked that the newly installed SBC has a short to ground. MB is going to replace the entire SBC, again, on Monday.

There were also 2 other errors unmasked as a result of the passenger SAM. 1 -- the windshield wiper fluid sensor is bad, which in turn is causing my coolant censor to malfunction and 2 --the parking lamp on the passenger side Xenon lamp is bad. They said the parking lamp can't be replaced. The only solution is to replace the entire right side headlamp module (E2) at a cost of $3,000. Any feedback here would be helpful.

The good news is that the Transmission modules, and everything else, were all fine according to SDS. They think the SBC or SAM could be causing a speed sensor malfunction leading to the unexpected downshifts.

It does seem odd that the SBC, passenger SAM, coolant sensor, parking lamp are all in series and all faulty.
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Old 07-12-2019, 07:18 PM
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Final Solution

Just to follow up for anyone else who might see this issue the ultimate cause of the unexpected downshifts while cruising along was the steering column module. Replacing it fixed the problem. An unrelated issue was passenger SAM failure. The MB dealer was unable to run star diagnostics until that was fixed. Even after SAM was replaced, there were NO ERROR codes indicating the steering module was at fault. I took a calculated risk and replaced it based on a post I found on BENZ WORLD . To recap symptoms:

1. Car downshifts at random, this could be because the steering module thinks it's getting a signal (false) from the down shift paddle.
2. When the problem occurs, using the upshift paddle causes a downshift. The downshift paddle is not operational.
3. The console shift will usually work and get you back to drive, but not always. Sometimes you have to stop and go to Park.

This was a tough one to figure out, I got lucky stumbling on an old post.

Last edited by ceberus; 07-12-2019 at 07:21 PM.
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Old 07-14-2019, 04:48 AM
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'13 C63 AMG P31 | '98 3000GT
Originally Posted by V8Thunder View Post
Hi all, new member here.

I have something to discuss and get people's thoughts on.

I've found that the downshifting in S and S+ to be too aggressive, ie the revs are way too low when downshifting, which results in jerky engine braking which is not only uncomfortable but also can't be good for the transmission.

I've found a workaround by driving in manual mode, but relying on the auto downshifting when I brake. I've found that the downshift now happens later on, and is much smoother.

My questions are - Does this approach have mechanical sympathy, and Do you do this too?

Thanks
Jack
C, S, S+ adapt to how you drive. If you drive like granny, they will shift like granny. If you drive aggressive, they will shift more aggressively. You can always reset this too.

1. Turn the ignition key to the "on" position which is just before you crank the engine to start.
2. Press the accelerator to the floor and hold for 5-10 seconds.
3. Then turn the key to the off position but do not remove the key, then release the accelerator.
4. Wait at least 2 minutes

When you go back out, get on it a bit more.

Other things to make sure are, that your car is fully warmed up. If you try and downshift or upshift while the car is still cold (numbers are blue) it can cause jerkyness. Once the numbers are white, still give it a little bit of time, but then you will notice the shifts are smoother. Warmer / colder weather will affect the warmup times as well.
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