Drive resistance

[mpwnbr]

A few weeks back my car decided to stop driving; their was power available but there was some sort of lock on the transmission or gears. Anyway, after loading it onto a flatbed truck, Mercedes repaired the car by fitting a new Transmission Control unit to the gearbox. All sorted I hoped. However since that repair the drive of the car has been so different, with the symptoms being a few fold.

Firstly there appears to be some sort of resistance to the drive. It's difficult to explain, but if I accelerate to a certain speed, lets say 40mph, and then take my foot off the gas, the car decelerates at an unusually quick rate. It's like there's something that's stopping the car from free wheeling properly. This is best demonstrated by driving down a hill, which I do and continually test on my daily commute, and when I take my foot off the accelerator, the car actually decreases in speed. Unfortunately CL600's didn't exist in Newton's days, and maybe his theories may have been a little different had they been around, but everyone of us knows that if you do freewheel down a hill then the speed will increase. Not mine!


Another symptom is the gear change of the car, which is certainly less smooth than previously, in fact quite jerky, and is then followed with higher revs than I seem to recall prior to the new Transmission Control Unit.

And finally, there's also another noise coming from the car, which can be noticed when driving along a quiet road with windows open. As speed increases the noise gets quicker and as speed decreases the noise gets slower. Imagine if you had a sticker on the surface of a new tyre; it's that sort of rotational/rubbing/friction noise. I've taken a look for a few possible issues such as warped brake disc with pad rubbing on it, but all discs seem to be the same temperature after a drive. I've also looked at the inner face of the tyres in case there's any delamination or other damage that could be providing this noise, but again there's no sign of a problem.

So this all brings me back to the Transmission Control Unit, and although I returned my car back to Mercedes earlier this week, they test drove it and put it on the Star Machine, they weren't able to pick up any errors or identify any problems.

So, as ever you guys are a wealth of knowledge and good ideas, so I was hoping for some more assistance.

Any ideas would be more than welcome.

Thanks,
Mark

 

[V6Matty]

id say possibly when coding the unit to the car they got it a little wrong or didn't apply the right settings, ask them to re do it from a software point of view and see if its any different.

 

[mpwnbr]

id say possibly when coding the unit to the car they got it a little wrong or didn't apply the right settings, ask them to re do it from a software point of view and see if its any different.

Thanks Matt. When the car went in earlier this week, it was suggested by the Service Manager that the issue could have been the coding or settings needing adjustment. Apparently these were looked at, and all ok. They were also reset but the problem remains.

I think we're all sensitive to our own cars and can pick up on the slight nuances, whereas others can't. However they've agreed for me to take the car back to them, to find a hill, demonstrate the phenomena, and then take it from there.

Again, any more suggestions?

 

[television]

Static test on the gearbox adaptations probably will not work, it needs live data to do this.

There should not be engine braking when cruising and you just ease off the throttle, this would make the car very uncomfortable to drive.

 

[mpwnbr]

Static test on the gearbox adaptations probably will not work, it needs live data to do this.

There should not be engine braking when cruising and you just ease off the throttle, this would make the car very uncomfortable to drive.

So how do you get the live data Malcolm? Do I assume there's a smaller hand held Star Machine that can be plugged in that will read the data while the car is driving?

And you're totally right about the drive being very uncomfortable. While the engine wants to provide power and the gearbox go through the gears with the speed of the car, as soon as you get to a point where you don't want gas and ease off the pedal it then feels like there's something grabbing hold of the power from the car and resisting it's freewheeling. It really is a horrible drive at the moment.

 

[John Laidlaw]

similar symptoms with mine, which is now awaiting a new Gearbox ECU (I'm told 18th. August....)

 

[television]

similar symptoms with mine, which is now awaiting a new Gearbox ECU (I'm told 18th. August....)

Not good is it when the cars makers cannot set things up or even say there is not a problem.

 

[mpwnbr]

similar symptoms with mine, which is now awaiting a new Gearbox ECU (I'm told 18th. August....)

A Gearbox ECU? Apologies for my terminology but I've just looked at my receipt, and what I've been referencing as a Transmission Control Unit replaced onto my car a month back, is actually an "electrohydraulic control unit of automatic transmission", so I'm thinking that's what you're having onto your car.

Unfortunately for me it's since the replacement of this that my problems have occurred. Hopefully you have more luck than me.

Out of interest for you, the job cost me £767.27 at Inchcape Mercedes. I'm awaiting this money to be reimbursed to me from the purchase dealership (see previous post), but I believe you will probably get this job done at half the price elsewhere?!

 

[television]

Yes all the same thing and part, the interesting thing is on the previous model gearbox this control unit would not have influenced or changed the gear shifts.

 

[John Laidlaw]

A Gearbox ECU? Apologies for my terminology but I've just looked at my receipt, and what I've been referencing as a Transmission Control Unit replaced onto my car a month back, is actually an "electrohydraulic control unit of automatic transmission", so I'm thinking that's what you're having onto your car.

Unfortunately for me it's since the replacement of this that my problems have occurred. Hopefully you have more luck than me.

Out of interest for you, the job cost me £767.27 at Inchcape Mercedes. I'm awaiting this money to be reimbursed to me from the purchase dealership (see previous post), but I believe you will probably get this job done at half the price elsewhere?!

Yes, same part. For mine they can't get a new one from Stuttgart until 18th August though. Also Inchcape Mercedes Liverpool. However mine is still under warranty , could be worse I guess, and with Mercedes I get a loan car until it's done (smaller dispute at the moment they've given me a B Class, they are promising to improve that/through Europcar their provider shortly).
Down side is the car is being changed end of August and I don't think I will see it or drive it again!

 

[John Laidlaw]

Not good is it when the cars makers cannot set things up or even say there is not a problem.

Exactly Malcolm, it took nearly 4 days for them to admit this was the fault, time wasted. In reporting it to Arval (My lease co), they said this was fairly common, and I was probably lucky it hadn't happened sooner!

 

[mpwnbr]

An update on this one for your thought please chaps........

I brought the car back to Mercedes yesterday, to take one of the Technicians out for a drive to experience the various phenomena that the car continues to experience.

I mentioned previously here how when driving down a hill, foot off the gas, instead of the car gathering speed, it actually decreases. This was demonstrated to the Technician, with the car in Drive, and then also in Neutral, noting when in Neutral the car gained speed. This wasn't seen as anything out of the ordinary by the Technician, explaining to me that when going up and down hills the car actually regulates the speed. I could understand that in perhaps a 4x4, where you would switch the settings when off-road. But I've never heard of the like before!

Regarding the general drive of the car, and the feel that there is something holding the car back, some sort of resistance from the box, again the explanation had me a little miffed. The technician suggested that with the new Transmission Control Unit, as opposed to the now replaced broken one, it could just be that the feel of the new unit is different. Now I accept that, but what I found hard to believe was the suggestion that the Transmission Control Units are intelligent, that they sense and learn from your driving style, and over time they adapt to that driving style, so in time the car will revert back to driving how it did previously.

These two explanations sound like someone is trying to pull the wool over my eyes. However you guys know an awful lot more about how these cars drive and the technology within them, so hopefully you can shed some light on this for me.

Thanks,
Mark

 

[John Laidlaw]

Mark I know that the gearbox has adaptive technology, which might be your issue indeed. I experienced this when I first got mine, in the first week there was definetely a jerky downchange to 4th., after another week, and up until the 17th. when the ECU became US, the car was smooth all through the gears, up/down (Reflecting my fine driving style of course ) and halt.
So I can accept that to some extent. I suspect there is something to be said on the 'free wheeling aspect' too, engine braking will be a factor of course. With my Hybrid I have to disengage the engine when going downhill (easy matter as there is a method) otherwise it will use engine braking even more than normal to build kinetic and engine charge. So I can accept there will be some 'resistance' when going downhill. How much? not sure, and I guess that's the issue, all subjective really. I'd give it some time to adapt to you and see what you feel after a few more weeks. I assume they will extend the warranty on this repair.
By the way you may have noticed my Black E300 in the corner of the yard when you were at MB Liverpool, looking a bit abandoned!

 

[mpwnbr]

Mark I know that the gearbox has adaptive technology, which might be your issue indeed. I experienced this when I first got mine, in the first week there was definetely a jerky downchange to 4th., after another week, and up until the 17th. when the ECU became US, the car was smooth all through the gears, up/down (Reflecting my fine driving style of course ) and halt.
So I can accept that to some extent. I suspect there is something to be said on the 'free wheeling aspect' too, engine braking will be a factor of course. With my Hybrid I have to disengage the engine when going downhill (easy matter as there is a method) otherwise it will use engine braking even more than normal to build kinetic and engine charge. So I can accept there will be some 'resistance' when going downhill. How much? not sure, and I guess that's the issue, all subjective really. I'd give it some time to adapt to you and see what you feel after a few more weeks. I assume they will extend the warranty on this repair.
By the way you may have noticed my Black E300 in the corner of the yard when you were at MB Liverpool, looking a bit abandoned!

John, that's a great reply, and really gives me a lot of comfort in what Mercedes were saying to me. It's good to have a lot of that reinforced. Having recently moved jobs I'm only doing 100/150 miles per week, with maximum journeys generally being 5 or 6 miles, so it may take some time for the adaptive technology to acclimatise itself to my driving style, so I'll give it some time and see what happens over the next month or so.

As for your car, it looks like MB Liverpool got their wires crossed.........surely you didn't ask them for the go faster stripes, spinny chrome alloys and whale fin on the back.......looked the part for your next drag race though!

 

[John Laidlaw]

damn, Mark you caught me, I did indeed ask for all those upgrades, along with an internal glitter ball and furry dice. My secret is out
Will be good to hear how your car progresses/ in the early days when you were on the look out and identified this one I must admit to feeling more than a few pangs of jealousy!
Seems a shame you don't get enough time to rack the miles up in it though, that's what they were designed for! Take care

 

[mpwnbr]

damn, Mark you caught me, I did indeed ask for all those upgrades, along with an internal glitter ball and furry dice. My secret is out
Will be good to hear how your car progresses/ in the early days when you were on the look out and identified this one I must admit to feeling more than a few pangs of jealousy!
Seems a shame you don't get enough time to rack the miles up in it though, that's what they were designed for! Take care

Apparently John the internal fit-out is tomorrow, ready for the weekend!

What you said about the car and when I was first on the hunt for it, it's funny how with the various troubles I've had with it, people ask me am I fed up with it, but I'm not. All I have to do is look at it, or even drive it when it's not performing properly, and it's still a pleasure. Mind, have you sat in the new S-Coupe in MB Liverpool. Wow, a thing of beauty!

 

[television]

Re these boxes and engine braking, it I am driving along a flat road in either of my 2 cars and lift my foot from the throttle, the car will of coarse slow down, but the slowing is not felt as any form of retardation. Sure it would go further in N, but nothing noticeable or uncomfortable. Going down hill is another story and engine braking soon comes into play, if I feel it is too much then I just lift the right paddle, and maybe just blip the throttle at the same time.

Re adaptation for driving style, this only happens on the actual journey that you are doing, gear box ECUs only have tiny memories, and how you drive today has nothing to do with how you may drive in the morning.

 

[mpwnbr]

Re these boxes and engine braking, it I am driving along a flat road in either of my 2 cars and lift my foot from the throttle, the car will of coarse slow down, but the slowing is not felt as any form of retardation. Sure it would go further in N, but nothing noticeable or uncomfortable. Going down hill is another story and engine braking soon comes into play, if I feel it is too much then I just lift the right paddle, and maybe just blip the throttle at the same time.

Re adaptation for driving style, this only happens on the actual journey that you are doing, gear box ECUs only have tiny memories, and how you drive today has nothing to do with how you may drive in the morning.

Thanks Malcolm. Your comment put me back to square one, but I need these opinions and experiences. Unfortunately in my car, when I am driving along a horizontal road, I do feel as though there is some sort of resistance slowing the car down. If I put the car into neutral straight away I can feel that resistance change from something that feels tight to something that feels loose; if you know what I mean. This phenomena is exactly the same going downhill, but what you refer to as engine braking. Prior to the new ECU the car would gain pace in D going downhill, whereas now it not just loses speed, but it feels like something is stopping it. Unfortunately it seems it might just have to be something I get used to.

As for the adaptations to driving style, all I can do is listen to others perspectives and knowledge of these things. I was hoping it would be as John explained, and hopefully in time things would improve.

 

[John Laidlaw]

Apparently John the internal fit-out is tomorrow, ready for the weekend!

What you said about the car and when I was first on the hunt for it, it's funny how with the various troubles I've had with it, people ask me am I fed up with it, but I'm not. All I have to do is look at it, or even drive it when it's not performing properly, and it's still a pleasure. Mind, have you sat in the new S-Coupe in MB Liverpool. Wow, a thing of beauty!

great, and yes I did sit in the S Coupe and I agree fully, what a beast/beauty combo!
you have a great car there, and these things will resolve

 

[John Laidlaw]

Re these boxes and engine braking, it I am driving along a flat road in either of my 2 cars and lift my foot from the throttle, the car will of coarse slow down, but the slowing is not felt as any form of retardation. Sure it would go further in N, but nothing noticeable or uncomfortable. Going down hill is another story and engine braking soon comes into play, if I feel it is too much then I just lift the right paddle, and maybe just blip the throttle at the same time.

Re adaptation for driving style, this only happens on the actual journey that you are doing, gear box ECUs only have tiny memories, and how you drive today has nothing to do with how you may drive in the morning.

Hmm... I was only thinking on the downhill aspect when considering engine braking. On the level, never considered at all.
I hear what you are saying on the gearbox ECU, but my thinking is that if you continue to drive everyday in the same way, it has already adapted that once (with it's small memory) and senses your style then. Interesting when you get a car back from service, do you notice the adaption has changed (Presumably if it's been Italian tuned during a road test!)? I drive quite consistently so I think my car is constant in it's reactions to my input....