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Bluetec transmission downshifts

 
Old 07-12-2012, 07:54 PM
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Bluetec transmission downshifts

When I take my foot off the accelerator the transmission seems to downshift and slows the car like a downshift in a manual transmission. This happens more a slower speeds.

Does anyone else have this experience?
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Old 07-12-2012, 11:02 PM
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If it happens only when the vehicle is cold you might be experiencing diesel bucking,a well documented problem with some recent Bluetecs...including mine.
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Old 07-13-2012, 02:31 AM
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Originally Posted by sgansky View Post
When I take my foot off the accelerator the transmission seems to downshift and slows the car like a downshift in a manual transmission. This happens more a slower speeds.
Does anyone else have this experience?
Depends on many factors. Hills, what transmission learned of ur drive style and if in comfort or sport
Mode. The ratios are
QUite close in lower range so a downshift is very normal. Or you lucked out and got the double clutch AMG speedshift. They can make that mistake on mine :o) Bamma Boys n Girls feel free july 27 double brown hahaha
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Old 07-13-2012, 09:48 AM
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Mine does it, too. Seems to occur mostly when slowing to a stop. At first I thought it was my imagination. Barely perceptible, but the tach noticeably jumps up a few degrees as the truck passes down through 10-5 mph. And as the deceleration increases immediately after the downshift, I have to reduce pressure on the foot brake to avoid a jerky stop, then increase pressure again to hold the truck at a standstill.

It may be the result of a learning experience for the transmission, because I drive it in sport mode and I often downshift on curvy mountain roads to help brake the vehicle. I have the Airmatic suspension and active curve options.
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Old 07-13-2012, 02:05 PM
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My 2006 gas used to downshift into first when slowly coming to a stop. It did so with quite a jar. The dealer gave another one of those "they all do it" speeches but did indeed do something to the transmission which all but (but not totally) got rid of the problem. I do not know what he did.
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Old 07-14-2012, 10:32 AM
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X350d GLE500e 2017, ML350 BlueTec 2012(sold), A200 2013, ML350CDI 2009(sold), Aston Martin DB7 2003
Yes mine changes down at low speeds, as well as at high speeds, especially in hilly country. Usually it greatly helps the driving conditions, although I must admit sometimes I do just want to coast steadily downhill, so I have to touch the throttle to get it to change up again.

And for the record, the Aston Martin does EXACTLY the same thing.
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Old 07-14-2012, 12:32 PM
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I have a new ML350 Bluetec too and have experienced this same thing. I don't think of it as a problem, but it is noticeably different from my 2007 R-Class diesel.

I have simply thought of it as "engine-drag," more of it, than in previous cars with automatic transmissions. In a car with a manual transmission, you were always aware of it and could use it a lot if you wished. Automatic transmissions always had a "free wheeling" aspect to them and engine drag was usually not very noticeable. I think some early auto transmissions had a roller bearing/ratchet kind of free wheeling device so that when you took your foot off the gas peddle, you were simply coasting... no engine drag at all. I could be wrong about that.

I think in recent years the ability to use the engine-drag feature has been added back to the transmissions as they have added the "manual shift" option to the transmissions. My 2007 R-Class also had paddle shifters. I NEVER used them except to experiment a little.

The paddle shifter lets you use available engine drag by letting YOU select the timing of the downshifts when slowing down. If you don't use the paddle shifter, the transmission itself decides when to do it, and it is much smoother and you don't get the sensation of engine-drag.

My immediate impression in the new ML, was that they changed the timing of the automatic downshifting... But... I am getting way over my head here in my speculations. I am not an expert in such things by any means.

Al
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Old 07-14-2012, 02:29 PM
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2013 ML BLUETEC JULY 31
Perhaps this is more noticable because of the torque converter change from 2011.
Much less slippage in the 7G-Tronic PLUS
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Old 07-15-2012, 06:12 PM
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Originally Posted by sgansky View Post
When I take my foot off the accelerator the transmission seems to downshift and slows the car like a downshift in a manual transmission. This happens more a slower speeds.

Does anyone else have this experience?
As long as it's smooth and comfortable, it is doing what it is designed to do. Enjoy.
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Old 07-16-2012, 01:42 AM
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Lexus is the only car that has no perceivable engine drag what-so-ever.
MB does it to help prevent brake pad and rotor wear. Also, it is the passive arm of distronic plus.
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