Is the 7g gearbox really that bad?

[jaymanek]

The 5g has a speed plate that definately comes seperately and is only around £200 or so.

VERY recently MB have started supplying the speed plates without valve body (for 7G) at around £250 but they have to be coded at a main dealer, most indies wont be able to code them in.

 

[BenzedUP]

The 5g has a speed plate that definately comes seperately and is only around £200 or so.

VERY recently MB have started supplying the speed plates without valve body (for 7G) at around £250 but they have to be coded at a main dealer, most indies wont be able to code them in.

That's it! Speed plate which cost around £250 your right but with all the work. etc.. set him back £700

 

[Mr E]

Try the big PDF file that's linked to the thread in the technical section under 7g. I'm on my iPhone app so doing a link to its tricky.

Clearly however from numerous documented issues with harsh down changes that MBs electronics don't work as well as the conventional sprag clutch.

It's also common sense. A 7g has two more gears, it needs more space and if it had a bigger casing it wouldn't fit within a transmission tunnel designed for a smaller 5g box. remove sprag clutch and hey presto 7 goes into 5...

Bar the W164 and W218 all MBs have been available with both transmissions. Why, because they fit into the same casing which fits into the same space in the transmission tunnel. As it were the W218 is 212 based which was sold with the vastly superior 5g box.

I did - he has that and more up to date MB documentation too. Nothing in the documentation he has about having to squeeze into a 5-speed case, so he was interested where your info came from. That pdf does state that a smaller one was planned but was never put into production...

It appears that the box isn't that different in size (I don't know, I just go from what he tells me from the tech specs) but it uses a different gearing system from plain ordinary planetary gears. In effect it acts like one set of gears inside the other. Removing a sprag clutch or two would not necessarily reduce the internal size requirement so funnily enough it's removed to reduce mechanical complexity and mass. Auto gearboxes and common sense don't always go together.

I'm quite happy to concede that it may not appear to be fantastic (doing away with the sprag clutch), and it does explain why a change/tweak in software can fix a clunky change. However, there are many out there who don't experience these issues either, me included. However, reducing mass in the drivetrain is a good thing and this is one approach toward doing to that. I guess there must be a million or two of them out there by now as well produced over the past 9 years

 

[Borys]

I'm with mine 50/50
Don't like its rolling down th hill or up,in S it jerk when shifting from 2nd to first when coming to stand still - aparently I cannot do nothing about it :-(.Otherwise all ok
I like when automatic pulls when foot of the brake,7g in C doesn't
Great mpg in 7g in my S500, avaraging 25.4 mostly town - pretty good

 

[sinewave]

Downshifts om my 7G box are fine, as are the upshifts.


My only gripe is the huge 'Satellite delay' when you mash the peddle for kick down on a sneeky overtake!

Don't bother now and use the paddles instead, far more responsive and what the box should do it's self under Max Warp Drive!



A little known feature of the gearbox I've only just found out about is the Shift + feature of the Stick and paddles.


If you have dropped to say 3rd or 4th via the gearlever or paddles for a sharp overtake you can get straight back to 7th or Drive by holding the Up paddle or Lever + for more than 1.5 secs or so.

 

[Paul/]

A little known feature of the gearbox I've only just found out about is the Shift + feature of the Stick and paddles.


If you have dropped to say 3rd or 4th via the gearlever or paddles for a sharp overtake you can get straight back to 7th or Drive by holding the Up paddle or Lever + for more than 1.5 secs or so.

Basically it selects whatever gear it thinks is optimum for that speed, what it would have been in if you hadn't intervened. My gripe is that I wish I noticed when I accidentally lean on the stick the other way, and restrict to current gear -1, which announces its presence pretty quickly as I find myself screaming along at moderate speed...

 

[st13phil]

I cannot comment on breakages or repair costs as I've had none, but based on my experience with the 5g 'box in my W204 220CDI, the 7g 'box in my wife's 2009 SLK350 and the 7g-plus 'box in my current W212, from a driveability perspective the 7-speed box is superior in every respect to the dull-witted, lethargic, 5-speeder.

As Mactech and others have said, it has an almost telepathic ability to be in the right gear at the right time, and the majority of shifts are largely imperceptible. Two capabilities that the 5-speed 'box in my W204 singularly failed to demonstrate.

 

[Mercy1]

WIth such diametrically opposed views expressed, can't help conclude that it all tells us more about the driver than the gearbox

 

[Paul/]

Perhaps, in addition to all the parameters the system monitors to assess driving style,
it's a bit like a horse that plays up for a rider that it knows doesn't like it very much?

 

[Ian Donkin]

The voice of reason.

7g is rubbish. I've sampled it from my car, to C320 and CLS350 and E500. All changed slowly and jerkily. All bar the petrol had a poor span of speed in 3rd gear meaning a 69mph change, just what you don't want pressing on or overtaking.

I've sampled vast amounts of 5g cars from 4pot diesels to V8 AMGs and all have been responsive, well spaced gearing wise and a joy to drive.

Olly and I are right, OP the rest are IMHO wrong.

OP made no statement of opinion, just asked the question!

 

[Ash]

I haven't added up the posts but i think quantitatively there's more support for the 7 speed. But support for old tech is still there, a bit like vinyl vs digital.

Foe my part i think the 7g plus on 212 is far superior to 5spd on 211 320cdi. The latter was often in the wrong gear and was basically clumsy. The new one isn't. It also lets you drive on the torque better.

Incidentally the engine braking seems to have gone with the 7g. probably more fuel efficient, but it is a bit disconcerting at times.

Have a drive and let us know which you prefer
Ash

 

[mct_cars]

5G in E270 CDi - good, 7G in E500 better. Mercedes tested the 7G out in the 500 from the 04 model year before using it in the rest of the range.

Both boxes are better than the archaic 4 speeder in the SL with no lock up on the torque convertor, and no starting off in first (even when in sport, it changes down from 2 to 1 when you mash the pedal.... cue pause). saying that the 4 speeder is a much much much smoother box at changing gears than either the 5G or 7G.

 

[Paul/]

I haven't added up the posts but i think quantitatively there's more support for the 7 speed.

I think it's a landslide if you count the posters rather than the posts

 

[Orwic]

I can't claim much knowledge on the subject, but my old car (c240 petrol) had a 5 speed box. Perfectly happy with it - responsive, smooth changes. But it failed, with not that much warning. Loss of power, pulled away very reluctantly, and eventually lost all drive, luckily just as I rolled up at home. Reconditioned box via my indy was the answer, and again happy. Now I've got a E320 cdi with 7 speed. So far so good: smooth changes, seems to be in the right gear more often than my old 5 speed. What I don't like so much is the way the car thinks about it for a bit before taking off if you put your foot to the floor. On balance I'd say I preferred the 7 speed, but I've only had the car about 10 weeks, so it might be a bit early to tell.

Good luck in your choice, whatever you decide to get!

Orwic

 

[kianok]

I love the 7G box in my 350.

The only harshness on dowshifts only happens while in slow traffic and it's only now and again.

Having come from VW's DSG box it does feel a bit slugish sometimes, but that's not a fair comparison.

 

[sspeed]

I have owned 2 cars with the 7G box..
A 2004 SL500 and a Late 2007 E320 Cdi.

Both boxes were fine...
In the E class it was totally superb.. Brilliant for overtaking on the motorway and I loved the way it used engine braking when going down steep hills (like a manual box)..
I remember reading that "transmission Lock up" occurs at a lower speed than on the 5G box. If I remember correctly the 7G locks up around 55mph, hence the better fuel consumption.

My E class did 1800rpm at 70mph and my current C270 cdi with the 5G box does 2200rpm at 70 mph.

Overall I rated the 7G very highly indeed..
My main gripe with it is the half ****d design of the way the ATF is changed. However that wont be an issue to anyone who doesnt dabble with such things..
One negative aspect of the way the fluid is added is that if you ever needed to top up then its not possible in the same way you can do it on a 5G box.

 

[BigSilverEstate]

7g cars to fit in the transmission tunnels designed for 5g cars go without sprag clutches so roll back on hills. Every 7g I drove would roll back on steep hills. MB rather than redesign the transmission casing and therefore transmission tunnels decided to make 7g fit into 5g casing. They should have waited to introduce 7g on cars designed to take it and engineer it properly, not quickly.

I have not done the comparison of the two gearboxes so would not weigh in in favour of either. I am interested to read the points *** makes here and elsewhere about the benefits of the 5 speed gearbox over the newer 7 speed version, viz: wider spacing providing spans without change up which are well matched to many real world driving situations; smoother shifts; cheaper maintenance and ?better reliability; quicker perceived response times. I think this is really helpful for anyone without first hand experience like me to help frame their evaluation of the relative strengths of the 7g i.e. more clever tricks to get the right gear for the situation, better reported economy, perceived seamlessness etc.

But I can't get my head round the specific point that designing to fit the existing casing was an indication of corner-cutting in the design process. Surely this must have been part of the design brief in the first place because of the major benefits of being able to phase in the new box without fundamental redesign of other aspects of the range? So they would presumably have made the gearbox this size and shape even given infinite time and resources. The question then would be whether they made the right design compromise in allowing rolling backward on inclines, or would another solution have been better.

 

[Paul/]

But I can't get my head round the specific point that designing to fit the existing casing was an indication of corner-cutting in the design process. Surely this must have been part of the design brief in the first place because of the major benefits of being able to phase in the new box without fundamental redesign of other aspects of the range? So they would presumably have made the gearbox this size and shape even given infinite time and resources. The question then would be whether they made the right design compromise in allowing rolling backward on inclines, or would another solution have been better.

Here's Dash1's take on that from another thread:

The only downside, if it can indeed be considered as a down side, is that I would have been concerned about the “hill hold” facility on the 722.9. Given what MB did with this transmission to incorporate the 6/7 gears, then it’s not surprising. To redesign a new transmission totally and then re-design the transmission tunnel to accommodate it would have been prohibitively expensive, as it would have meant and involved a new series of crash test analysis as the transmission tunnel is actually and forms part of the vehicles overall structure and stress/crumple zone areas. MB opted for the earlier use of the current 722.6 housing/casing and removed the sprag mechanisms, which was a much cheaper option. For those that do drive the 7-speed, you may have noticed that 722.9’s actually roll backwards with your foot off the brake. Some, I am led to believe believe have a hill holding feature where they use the brakes to hold briefly, although I have never personally driven one to confirm this,

The reason for the change is this, when the 722.9 transmission was commissioned, the design criteria was such that it had to fit into the same transmission casing as that of a 722.6, as it was already being fitted into vehicles already designed and in current production. If you change and/or modify the transmission tunnel as said above, then you have to repeat all the crash testing evaluations, as it is a crumple zone. Since the 722.6 has five gears and the 722.9 has 7 gears, the extra Ravigneaux gear sets that makes this possible has to fit into the same casing, necessitating and requiring something of non-critical components to be omitted. From the 722.6 designs, the two sprag clutches were removed. These units are essentially freewheeling elements that rotate in one direction but lock up in the another, without them, a transmission will not lock up when it rolls backward in 1st or 2nd gear on any form of gradient. If you have ever wondered why a 7-speed automatic doesn't hold on a gradient like the 5-speed automatic does, well, that’s the reason and it’s not a fault to be concerned with, so MB says anyway.

 

[NISFAN]

7G is a good box if you ask me, but not as accomplished as the new stuff from ZF

 

[Mr E]

But it's not in the existing casing.... Master E confirmed this with his tutors today. It roughly the same size becasue by using more complex gearsets it can produce more drive ratios with the same number of gear set placings.

Including the Ravigneaux gears and removing the sprag clutches (with their need being made "redundant" by a nifty synchronised shifting mechanism) is to do with the reduction of mass in the drivetrain.

The fact that a sprag clutch locks up when rolling backwards is a nice "to-have" but is not the primary function - they are there to smooth shifts, allowing a smooth take-up of torque onto a shaft. Other uses of sprag clutches include helicopters (allowing the shaft to continue rotating when the engine fails) or on a bike (where quick downshifts could cause rear wheel lockup when road speed and engine speed are not matched).

If you're going to increase the number of gears with the main eye on improving economy, why are you going to increase mass? Makes no sense for an OEM to do this in today's environment - the game is all about reducing mass, particularly reciprocating mass in the drivetrain.