Problem with 7 Speed Gearbox

[Dieselman]

Brian
I've read a few reports where it's commented on the 7G box hunting between the ratios. It's as if there are too many to chose from and being closely spaced it is programmed with tight tollerances so changes up and finds it's labouring sligtly so changes down and finds it could drive a higher gear, and so on.
I've also heard of banging in the lower gears especially when changing down.
Not sure there's a fix for this "feature".

 

[Brian WH]

Brian
I've read a few reports where it's commented on the 7G box hunting between the ratios. It's as if there are too many to chose from and being closely spaced it is programmed with tight tollerances so changes up and finds it's labouring sligtly so changes down and finds it could drive a higher gear, and so on.
I've also heard of banging in the lower gears especially when changing down.
Not sure there's a fix for this "feature".

If that is a feature I would like quiet words with the designer mate.

The main problem is not the hunting, that in a way I can understand, but it should not jerk when changing UP, even my wife can manage that in a manual. oops hope she is not reading this.

It shouldn't do it so they as I said will sort it.

 

[grober]

Having just read the service alerts I didn't like the bit about the circlip and spring but would have thought that applied to boxes earlier than yours Brian. Sounds as if you are in "no-man's-land" between software and hardware conflicts. The software is adaptive and the hardware wears/beds down. Presumably the software learns from your driving patterns and adjusts valve settings accordingly HOWEVER it probably expects the hardware to be immutable, which it should be ,within reason, but it may change markedly during the running-in period . If some of the parameters in the software havn't got enough "bandwidth" to cope then conflicts may occur and control may stray out of calibration range of the system in some situations. Resetting the control system to its default values may help temporarily until everything settles down but if the hardware profile has altered too much from its design spec then it wont cure the problem, just mask it for a while.

 

[Brian WH]

Just an update, for those interested. Those that are not look away NOW.

Having driven it around for the past 10 days, with lots of town driving, the gear changes are now hardly noticeable. Still it is at it's worst when it is very cold and a cold engine. For the last few days it has not been cold enough to notice in reality.

The dealer has told me they are waiting for another flash update from the boffins, for my car. Which is a very current one, as mine is up-to-date at the moment. Mind you resetting it made it worse last time, but we shall see when this new one arrives.

Watch this space.

As an aside, the service bulletin above was drawn to the attention of the dealership. and they said it is for later boxes than mine would you believe. Thought the latest boxes were supposed to be perfect.

 

[saorbust]

My old 5 speed is a little clunky as you describe in the cold engine, cold day scenario. Wonder if its the ATF warming up....

 

[Brian WH]

My old 5 speed is a little clunky as you describe in the cold engine, cold day scenario. Wonder if its the ATF warming up....

Good point.

I also wondered whether they had checked the levels.

 

[DieselE]

Having driven it around for the past 10 days, with lots of town driving, the gear changes are now hardly noticeable. Still it is at it's worst when it is very cold and a cold engine. For the last few days it has not been cold enough to notice in reality.

If the weather forecast is right there's some good testing weather coming up.

I'm sure that the comment about cold fluid has something going for it.

 

[Ultymate]

I can only speak for the 5 speed boxes, they are designed to hold on to first and second gears longer on cold startup to fascillitate a quicker warm up of the cat or cats, whether this holds true for the 7 speeders I know not

 

[Brian WH]

, whether this holds true for the 7 speeders I know not

The answer is yes mate.

 

[Brian WH]

An update on mine.

I had a courtesy call from MB HQ on Friday, asking me how my CLS was going. I said very good apart from the gearbox problem I had. She said she would contact the Dealer and get it fixed. On Monday I got a call from the Dealer and it is going in next Tuesday, with hire car available.

To be fair the gearbox is 98% OK as it was really only in the cold weather that it jerked in the lower gears. Now it very rarely jerks so I have not bothered to do anything about asking for the promised flash upgrade. I do not want it to go back to the problem I had when it was last reset.

I will let you know the outcome.

 

[ddentrec]

I recently visited the MB museum in Stuttgart: they had a S-Class development car with the 7G gearbox (see photo with my yoing son and the Mercedes fatory tour guide). Whn inside the car you had to wear headphones and the whole car, imcluding the dampers, were connected to a simulation computer.

They ran a program that emulated low-speed town driving as well as hard acceleration. Even the sound of the electric windows operating was added. But of course the car did not actually move: but it was so realistic as to be unbelievable.

Point is that the gearshifts in the 7G simulator were, well, non-existent and smooth as silk.

 

[Brian WH]

Well car went in today. Had C Class 180k for a couple of hours, totally gutless.

Anyway they updated the software which included a test drive and resetting the gears with the software programme, so that the gearbox knew when to change!! Thats the theory anyway.

Seems fine when I picked it up. We shall see especially next winter. I was told to speak to the Customer services girl personally if I had anymore problems. Very nice but stunk of perfume.

Having had a weekend away the car was filthy, and they cleaned it inside and out - Thanks very much, saved me a job.

 

[DieselE]

I was told to speak to the Customer services girl personally if I had anymore problems. Very nice but stunk of perfume.

And did your wife believe you when you gave this as the reason why the car stank of perfume?

 

[Brian WH]

And did your wife believe you when you gave this as the reason why the car stank of perfume?

That was before they cleaned it mate.

By the way after two days still going fine, the car that is.