Auto downshift while braking
 

I have mixed feelings on this - What do y'all think...?

While braking, particularly under 25 mph, my 2012 ML350 will noticeably downshift. You'll actually see the RPMs jump and feel the transmission "assist" in slowing the vehicle.

On the upside, I suppose this may reduce brake wear. It also gives me the torque I expect to accelerate.

On the downside, it's harder to brake to a stop smoothly. I don't mind it so much myself, but can be embarrassing with passengers. As the gears grab, I instinctively let up slightly on the brakes (around 20 mph) but then end up braking harder to stop (false confidence, I suppose).

It's not a huge deal and I only recently figured out what was happening. Maybe I'm still used to my old Rover HSE.


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Engine braking assists in stopping the vehicle and keeps the vehicle at optimum engine speed for acceleration. If you were manually shifting a car or motorcycle, you'd match shifts under braking, so wouldn't you imagine an automatic will do the same thing?

Sure, I get that. I've just never noticed it (let alone to be so pronounced) in any other car I've driven.


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I have the same issue in my 2013 ML350 Blutec. In fact, with AC runing downshifting is more jerky and it is almost impossible to smoothly decelrate to 0. I really do not like the brake feel with the transmission downshifting with the speed decreasing to 0. Thats pretty much the only gripe I have for this vehicle!

How many all-time-four-wheel-drive vehicles have you owned before ?

Different feel, you will be surpised if you open minded on adjusting driver patterns..

I don't think it has anything to do with the fact that it is a 4-wheel drive. But if it does, then MB needs to fix it. I have owned other 4-wheel drive vehicles (Lexus, RangeRover) and this is not typical behavior.
In the ML, the initial brake input feels spongy until you depress the pedal a little more when the brakes grab quickly and that's when you start overcontroling the brake inputs. I have tried another ML2012 and it is pretty much the same thing. I would say, the ML electric brake system need tweeking at low speed.

Try complaining about it the next time the car is at the dealer.

About six months ago, I complained about abrupt downshifts while coming to a stop, along with stumbling while the engine was cold. (I exaggerated the severity of both because MB dealers won't check for software updates routinely. There has to be a a specific customer complaint, or official recall.)

They did find a software update for the transmission control unit that seemed to help somewhat. I don't know whether the update was designed to address these particular problems, though.

Same here on both issues. I really did (and still do) feel that something isn't right. Of course, the dealership said that everything seemed normal.


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Abrupt Downshift
 

Same exact issue, seems to happen at when slowing down and at 20 mph. It is quite abrupt. My dealership wasn't able to find any software update that corrected it. Had it in 2 times and they said they see no error messages and couldn't recreate it themselves. It seems to have started at around 14,000 miles and I agree it's more significant with the A/C on. Since it has been colder here in Florida and I haven't had the A/C on when I first start the car, it doesn't seem to be doing the downshift. It will be interesting to see if it starts up again when it's really warm out. So frustrating though that they aren't able to see any message that something is wrong.

mine is smooth' noticeable,but smooth and no problem for controlled braking....see your tech.

mlee

Reviving an old thread here, to share my experience: my 2013 ML550 has the same issue, while braking to a stop (on flat terrain) while it downshifts it brakes by itself a little stronger, even though the pressure I keep on the pedal is the same. It may be because of the turbos and the extra "vacuum" they create when up-shifting (higher rpms, more vacuum created I guess).
When braking more aggressively the jerkiness is not so noticeable. Also, if I put it in neutral from 30 mph to a full stop, the brake pedal feel and action is smooth as it should.
On my previous 2006 ML350 the brake feeling was always smooth to a stop, regardless of terrain and didn't had to put the transmission in neutral.
So, for me it looks like a miss-match between rpms after downshift and the car's brake booster pressure at low speeds. Could it be addressed with a software update?

Turbos create positive pressure. Of course, there is vacuum on the intake side of the turbo but that would have nothing to do with slowing the engine down. The engine creates the vacuum and will slow the vehicle down without the addition of fuel and air.

The ML550 has the 7G-Tronic correct? The 7G is clunky on closed throttle decelerating downshift. The only time the 7G is happy is when the gas pedal is on the carpet. All other times it's balky, hesitant and slushy.

I've only owned two 7Gs and driven only a couple dozen, but I've never had a hint of "balky, hesitant and slushy." It's actually a pretty impressive transmission, learning your driving habits and drive preferences and responding appropriately.
I think it's better than the ubiquitous ZF-8hp, whether you want smooth, or fast. But they're both good trannys.

The downshifts mentioned above don't sound normal. It's worth having a tech look at it. Maybe at least smell the fluid.

Thanks @mikapen . The clowns at the local dealer changed the fluid at 60k miles earlier this year. It seemed to help the shifting, but I admit this could be psychosomatic on my behalf.

Clunking is commonly reported on this site for the 7G. Read all of the forum sections.

The ZF 8 speed is worlds apart from any box MB produces. As are Aisin transmissions. MB has poor transmissions in comparison to ZF and Aisin, and MB should exit the transmission part of their business and instead use ZF and Aisin.

I have had multiple vehicles with Aisin and ZF and they are stellar. The BMW versions of the ZF8 are titillatingly enjoyable to drive.