ATS

For those of you with 7 speed transmission, do you hold the shifter to the left to accelerate or slow down? In other words, let it find optimum gear?

My results with it have not been that good.. It shifts too low on cornering (1st gear!) - after that I stopped using this feature..

FirstMB

If you pull it to the left, and hold it for a couple of seconds, then the tranny will automatically downshift to the optimum gear for acceleration. Of course, you'd do this coming out of a turn, and on the gas. Also, you'd do this if you're getting ready to overtake someone on the road. Similarly, you can just stomp on the gas as well, and it will downshift to the optimum gear, but pulling the stick to the left, and holding seems to get it to downshift a little quicker. You do NOT want to this to slow down like you'd with a manual transmission.

marksatex

Are you saying NOT to downshift? I have been, not like a wild man but a little here and there in tight turns etc.. IS downshifting bad for the 7 sp?

FirstMB

Downshifting for the purpose of "engine braking" is bad for any automatic transmission...that's what your brakes are made for.

MadManAboutTown

Downshifting should represent no problem for this transmission, since it is built to withstand this kind of treatment, within reason.

Of course, you can wear anything out if you abuse it... but manually downshifting to slow down every now and then should have no negative impact on your transmission.

Besides, it's fun!

glojo

Am I right in thinking that an automatic gearbox works by the 'friction' of the oil?

When using engine braking would this be similar to putting a 'reverse' type friction or drag on the oil?

It might be better for 'MadManAboutTown' to help me understand how engine braking will work on an automatic? (emphasis on automatic).

I can understand how you can brake, fetch your speed down, and then change down to get the automatic to select the 'optimum' gear for the speed you are travelling at.

Regards,
John

MBZFAN55

During "hot laps" at an AMG Challenge 2002, the professional driver was down shifting almost MORE than he was using the brakes. I'm sure there is additional transmission wear, but I am also sure that MB wouldn't provide a "manual" option if they wanted us to always remain in one gear. It seems to be even more inviting now that MB is providing paddle shifts on the steering wheel.

MBZFAN55

My results with it have not been that good.. It shifts too low on cornering (1st gear!) - after that I stopped using this feature..[/QUOTE]

And btw I seem to have the same situation in my 04 S500, where the downshifts ALWAYS seem to have me in FIRST gear regardless of my speed. Mucho rpms !

FirstMB

Remember, my comment was that engine braking is "bad" for an auto transmission. The key word is "bad", which means the same thing you've said..."I'm sure there is additional transmission wear".

Race drivers do this all of the time, but then again, they don't drive their race cars until it has over 100,000 miles WITHOUT rebuilding the engine, or tranny.

MadManAboutTown

Be my guest and read up and how automatic transmissions work: http://auto.howstuffworks.com/automa...ansmission.htm.

And it is no secret that frequent oil and filter changes will extend the life of your transmission.

glojo

I can certainly see where your username comes from

"""""So the rotation is negative 2.4:1, which means that the output direction would be opposite the input direction. But the output direction is really the same as the input direction -- this is where the trick with the two sets of planets comes in. The first set of planets engages the second set, and the second set turns the ring gear; this combination reverses the direction. You can see that this would also cause the bigger sun gear to spin; but because that clutch is released, the bigger sun gear is free to spin in the opposite direction of the turbine (counterclockwise).
"""""""""""""""

It is bad enough being on morphine, but........... reading several pages of the above has sent my head spinning, and I am definitely none the wiser.

Thanks anyway for the link, but if anyone can explain in English how to carry out engine braking with an automatic I would be grateful.

I have seen any number of automatic cars that literally boil their transmission fluid when towing caravans or heavily laden trailers.

Regards,
John

SAguirre

I don't know what information you are basing this on, but you are not correct! Sorry.

I have always used the transmission to engine brake when driving down the mountain passes on I 70. My whole family has done this since the 1960s! We have never had any automatic trans. repair (this includes 3 ton Cadillacs).

One thing that should be noted about the 5 speed MB transmissions is that the torque converter locks in 3rd, 4th and 5th gear. This means that there will be no sliping of the torque converter turbine and cause extra heat to accumulate. This makes the AT of MB equal to a manual trasmission.

My choices are simple: I either downshift and use my engine to stop the car (in 3rd, I maintain 65 MHP or approx 103 Km/Hr). I could leave it in drive (5th) and coast down at about 130 to 140 MPH (I have done this only once, just for fun and to prove my stupidity). Or lastly, I could burn up my brakes and warp my rotors. I chose to downshift and use the engine brake. If this in done correctly, there is absolutely no negative effect on the transmission.

After 130,000 mils on my 300E, each time the ATF was changed (every 30K miles) the fluid was as red as the new fluid. Overheating is not an issue since the ATF cooler does a great job and the outside temperature is well below freezing.

Now it is time to get in my car and head up the mointains! I have a Mon and Tues off!!!

Steve A.

glojo

Hi Steve,
Now that I can understand. Are you fetching your speed down to the required speed and then selecting the correct gear?

Or are you belting along at high speed (100mph) and then just putting the gear into say second and letting the engine do the braking (or breaking)

That is the bit I cannot understand!

Regards,
John

SAguirre

Good Question!

I don't let my car run away and then make the transmission slow the car down. I don't think that is good practice. I usually make it up the mountain passes in 4th gear and sometimes third gear. If traffic is moving at 70MPH, then I would probably have the car revving quite a bit more in 3rd. However, once I am at the top of the pass (in one case it is after I get out of a long tunnel that has a 50 MHP limit), I am never in D, otherwise the car will run away. I leave the car in 4th until I get to about 65 or 70 MPH and then put in 3rd. Then I coast down the pass for about 9 miles and never touch the gas or the brake pedal. One interesting observation is that the engine temperature drops from half way on the gage to about 1/4 or 1/8 (depending how cold it is outside). This is caused by the high RPMs with no fuel burning. The -20 C temperature air coming into the engine makes the temperature drop really fast. This would also mean that the radiator is cold and would dissipate any heat from the transmission. However, I don't think that the transmission is very hot since there is no slipping in the torque converter.

Whenever I need more speed I will temporarily put it in D and then back to 4th or 3rd. I never go down to 2nd and I never make the transmission slow the car down, I make the transmission maintain the speed and not allow the car from accelerating. I have always driven stick shift cars (except for one Cadillac and my 300E), I also have a very good understanding of what my power train is doing. I am also very easy on my brakes!

This Christmas I saw yet another 18 wheeler truck have its brakes catch on fire and take the runaway ramp. I have once (in my old 300E) had to accelerate and drive well over 100MPH down the mountain since I had a runaway truck behind me!!! Looking in your rear view mirror is very important when driving on prolonged down hills. There is always some idiot burning their brakes and then loosing them.

After I finish cleaning my house, I am leaving for Vail and I will downshift yet again!

Steve

glojo

Hi Steve,
Yet again we are in total agreement, you are driving in a sensible, safe manner.

Hopefully I am not going to far off this interesting topic, because we are talking about fetching the speed of the vehicle down, and then holding the 'shift' (gear lever) across to the left to select its optimum gear for the speed that the drivers has chose to negotiate the hazard (instructor talk for bend)

John

SAguirre

I do drive kind of sensibly. But I also think that serious downshifting should be OK as long as the engine and transmission are at operating temperature. I might have hit 5,000 RPMs while downshifting once or twice in this car already on certain occasions. My 1991 300E had that done to it at least 15 times over its life. Nothing ever happened.

I sometimes downshift (engine brake) if I have just passed a slow-driving car and I don't want them to see me hitting the brakes right away after passing them. But again, the car is usually in a low gear already.

I am of the opinion that these transmissions are designed to take some severe abuse. I am not one to abuse mechanical things for no reason, but I would not feel to guilty or worried if I did some severe downshifting every once in a while. Mercedes Benz automatic transmissions are very reliable and durable. I don't know much about the 7 speed transmissions though.

Steve

scorchie

Correct or not correct is a subjective term.

Braking with the transmission/engine creates additional wear on the transmission or engine. It produces more friction on the clutch packs than would otherwise be encountered if downshifting were not done. Of course, this friction also occurs in normal use of the transmission.

The point is, the brakes are a lot easier to replace as a wear item than clutch packs in a transmission.

So, drive how you'd like, it's OK for the car. Just keep in mind that frequent downshifting will require sooner replacement of parts inside the transmission. Frequent braking with brakes will require sooner replacement of brakes.

(If you've seen the price of MB transmission work... you might start to think in a manner different than you do.)

-s-

(Been planning to replace clutch packs on my 190,000 mile 190E for the past 6 months... never get around to it.)

SAguirre

This is very true and well said. What you have to keep in mind though is that some of the downshifting done is not any harder on the clutch packs / bands than accelerating hard. Also, when I coast/engine brake while in 3rd or 4th, the torque converter is locked and eliminating any slippage that cold cause heat in the transmission. And at this stage, the clutch packs are not slipping. The engine is then acting as an air compressor and eliminates the heat. If the engine is well lubricated (which mine at least is) then the amount of wear on the engine and transmission is insignificant. If I used the brakes, however, they would be red hot!

When I drove up Pikes Peak they have a check point at the half way point of the return. My brakes on my 1991 300E were at a whole 97 degrees F, body temperature. My ATF was not cold, but definitely not hotter than if I were in stop and go traffic in a hot summer day. The people at the check point made you pull over if your rotors get hotter than 300 degrees F and the man said that the highest he has see that day was 700 degrees F!!!! My car was the lowest of the day.

I am sure that I am wearing my car's engine and transmission some, but the downhill is less wear than the drive UP the pass! If I truly wanted to baby the car, then I would not take it up the mountains 4 times a month. But since I do, I always flush and replace ATF.

On the other hand, severe downshifting is no different than sever up shifting. So I avoid both. If you ask any experienced mountain driver, they will agree that using your brakes to maintain the speed of your car down is idiotic. Brakes are to be used in cases when someone pulls in front of you or in emergencies. They are your back up safety system when driving miles of 6% + downhill grades.

So I know that we are talking about two cases of downshifting, but I think I clarified what I think of both.

Steve

scorchie

True that severe downshifting is no different really to the transmission than sever upshifting; however, if you only do one of them, then you are probably only putting 70-80% of the wear on the transmission than if you did downshift. The point isn't that it is hard or not; it is that it is additional wear and it causes the transmission to suffer more wear.

Holding a gear doesn't cause the wear; the shifting does. So, it you brake (with your brakes) to the desired speed, then down shift using the gas to match revs with your desired speed/gear, you will cause less wear than trying to "shock" the car to slow down with a downshift. This is how I use the gears to hold my speed in the mountains (as a snowboarder, I am there pretty often; plus, I live in California, not Kansas! ).

-s-

ATS

Also I have noticed that the AMG vehilcles will always downshift while braking. I am sure the engine can take it, although severe downshifiting (hitting high revs) is bad for the transmission and engine as severe upshifting..

So, although this is an amazing thread, how many people use the shift into optimum gear (by holding the shifter to the left for 2 secs)?

CASL55

When I read about this feature, I thought it was neat, but bow that I have cars that employ it, I never use it. If I'm going to downshift, I know what gear I want to be in, and I can tap the paddle or lever the appropriate number of times.

I think this feature could have been an artifact of the transmission programming, and the marketing folks decided to feature it. It actually gives the same effect as tapping the lever many times. Do you suppose early programming didn't adequately debounce the lever contact closures and this effect resulted?

Jim

glojo

I think I am right in saying that the AMG has a 'Speed Shift' gearbox which is slightly different and is designed to take this type of 'abuse'.

I have always taught my pupils to fetch their speed down, change down and then manouvre. I am not one to think that techniques either right or wrong and as technology improves sowe must adapt, but so far I have not read anything here that would improve upon the driving skills that are used on the public roads.

SAguirre and I seem to be singing from the same hymn sheet, but perhaps explaining ourselves in a different manner.

I wonder how many modern drivers could cope with driving a manual (stick shift) vehicle with a broken clutch? Off topic slightly, but it highlights how to fetch the speed down before changing down and NOT causing any damage to the gearbox. If you 'crunch' the gears you are not doing it right.

Regards,
John

JimPurdy

John,

You are showing your age again! Manual transmission? How many drivers under the age of 50 have even recognized a car with a manual transmission?

I think the intent of the MB transmission features were to give us "old folks" the sence that we still have a little control of the transmission since they did away with the clutch. I agree with Steve that it is better to use the transmission than brake in the mountains. I fried the brakes only once and I will abuse the engine and transmission before I repeat that action.

Jim

glojo

Nice one Jim,
In the UK the younger generation tend to view 'automatics' as being one step up from perhaps owning a diesel. No, just been told that they are both as bad as each other. No way would my son own either. I waste my breath telling him that Mercedes-Benz make a C30AMG Diesel or Volkswagen make a Golf GTi manual diesel.

Automatics are still not a popular option, I don't think my son has ever driven a vehicle with an automatic gearbox. Also if you take your driving test in one then you are not allowed to drive a manual.

Nice to hear from you,
take care
John

JimPurdy

John,

How can we import the manual shift preference from your youth to ours? Our driver education just consists of some classroom instruction so they can pass a ridiculously easy test and driving around with an instructor at 10 mph under the speed limit! I couldn't even find a driver's education company that had a manual transmission 12 years ago when my daughter was learning to drive. I have seen many letters to editors complaining about poor drivers but we don't teach our youth the basics and our police not only don't issue tickets for obvious infractions, they drive that way themselves. We seem to consider driving a basic right instead of a privilege.

Jim