Knocking on steering on new GLC

[HotJambalaya]

Not sure if this has been posted here yet?

http://www.honestjohn.co.uk/news/mi...g-of-motor-ombudsman-over-glc-crabbing-issue/

 

[dejongj]

It has but doesn't hurt.

Someone asked me to slow the video down, so I did...Here it is;

https://youtu.be/rvnZEOqCrQg

 

[trapperjohn]

That is ****e and totally unacceptable. Good Luck with your fight with Mercedes. And winter tyres would solve that. hmmmm.

 

[Tony Mac]

To help paint the picture - video of our GLC 250d AMG Line on 20" wheels,

https://youtu.be/E9vpoYz0Mswrr

It's worth noting that the stabilisation software on the camera actually reduces the impact on the video of the juddering and bouncing felt inside the car

 

[grober]

Having watched the video footage and read the experiences related by various owners I am coming round to the idea what they are experiencing is a form of transmission wind up rather than tyre scrub. Can anyone confirm the transfer box contains the usual 4 matic electronically controlled multiplate breakaway clutch or is it simply an open diff ? Has its control electronics been re-calibrated for the change in torque split 45/55 to 31/69 for example? Does it use extreme steering angle signals from the steering angle sensor to inhibit centre diff partial locking up at slow speed like some systems . Without knowing all the logical parameters that control the 4 matic system its impossible to say but I 'll wager the answer is something like that.

 

[dejongj]

I'm with you on that one. It is what I likened it to from the first moment when I reported it to Mercedes two months ago.

 

[brucemillar]

I'm with you on that one. It is what I likened it to from the first moment when I reported it to Mercedes two months ago.

it is also what I have described in every post I have put up on. It's threads.

 

[talltrees]

I have a 220 sport on standard 18" wheel had it 10months and not really noticed anything. However in the recent snow it has been very noticeable in the snow and feels as if it is understeering. It feels like it is skipping and running wide but the tracks in the snow run true with no deviation. So my take is it is definitely within the drive train. I also think it has been doing it more than I realised and just thought I had gone over a bump. It is a bit ironic that the main reason we bought the car is beacause of a steep drive which the Mrs won't drive in her C coupe Pan Evo with huge rear boots. Not to happy with how it handles the snow over the last few days, it does not inspire confidence, but the extra traction is a winner.
Due for a service soon so I will add to list which incudes the wind noise, loose emblem on tailgate, stange noises from behine the dash a few minutes after start, and the ICE crashes and freezes like an old PC.
This is our 3rd Merc and have come to the conclusion that are not what they used to be!

 

[Rowanlaw]

I am/was on the verge of buying a GLK 250 AMG Line. Loved the car and didn't experience any problem on test drive.However, I picked up on this furore and questioned the dealer more thoroughly this morning. Their response was interesting; I was asked to speak to a senior technician who informed me the 'characteristic' is a 'by-product of the Mercedes 4MATIC system' caused by 'an in-balance between front and back wheel speed'!!! He didn't want to take questions but the salesman made it very clear that 'there is no fix from Mercedes and will be no fix' and 'its just the way it is'.

 

[dejongj]

I am/was on the verge of buying a GLK 250 AMG Line. Loved the car and didn't experience any problem on test drive.However, I picked up on this furore and questioned the dealer more thoroughly this morning. Their response was interesting; I was asked to speak to a senior technician who informed me the 'characteristic' is a 'by-product of the Mercedes 4MATIC system' caused by 'an in-balance between front and back wheel speed'!!! He didn't want to take questions but the salesman made it very clear that 'there is no fix from Mercedes and will be no fix' and 'its just the way it is'.

Unfortunately that is exactly the kind of response we have all been getting. And dare I say, technically speaking I don't think he is wrong. The issue is that they don't recognise it as an issue and won't fix it; if they can.

I'm glad to hear the message is going out to prospective buyers as buying a car should be a 'happy' a 'feel good' purchase not this world of pain we've ended up in.

 

[brucemillar]

'an in-balance between front and back wheel speed'!!! is'.

That is normally known as a "spin" when the rear wheels starts going faster than the front wheels :^)

Does he not mean "an in-balance between the inner and outer wheel speed? Or the wheels on the same axle?

That causes the wheels to jump as they try to match speed from inside to outside. Normally this is allowed for in the transfer box/diff and if it is not? You get transmission wind up, or in the case we see here? The weakest past of the drive train (the tyres) unlock the windup by jumping. This means that the entire drive train is under massive repeated strain as the tyres bite then release then bite again.

 

[grober]

Taken from All Wheel Drive Explained | awd cars, 4x4 vehicles, 4wd trucks, 4motion, quattro, xDrive, SH-AWD, Haldex, Torsen, wiki - How it works

Assuming that the "differential lock" function on the same axle is taken care of by Mercedes usual selective braking via the antilock/stability control system then cross axle transmission wind up should not be a problem. On the front axle there might be steering scrub if true ackerman steering is not present [ i.e. each front steering wheel to be at a slightly different angle in order to trace out a slightly different curve radius]---- I guess when the wheel is driven this might present as a series jumps or clonks????

However- the front and rear wheels also have trace out a different curve radius. Again wheels on the same rear axle present no problem with an open diff.
Which leaves us with the prime candidate for transmission wind up [ front to rear- not side to side!] IF!!! the centre differential is locked or close enough to locked meaning the front and rear wheels can't rotate at sufficiently different speeds while necessarily tracing out their different radius curves.
My theory is that some sort of effect like this may be exacerbated by the 39/61 torque split if indeed LHD cars don't suffer from this with their 45/55 split ?

While for driving on grippy pavement at slow manoeuvering speed at full lock it might be useful to program the centre diff to disengage at high steering angles its possible to envisage this as a situation where full 4WD might be very advantagous when trying to manoeuvre/ start off on very slippery /snowy conditions. Its perhaps the sort of ability lots of owners would expect ---nay demand from their 4WD vehicle. In the old days all these differential locking actions were manually selected by the driver as appropriate to conditions but now its all automatic meaning perhaps there has to be compromise somewhere.


or something like that.

 

[talltrees]

If there is a compromise then current advertising is not very accurate; I have lifted the following text explaining 4matic from MB web site today:-

"Adaptable
When driving in a straight line, all four wheels normally rotate at the same rate. Rounding a corner, however, forces the two outside wheels to travel a longer path than the inside wheels. That means the left and right wheels must be able to rotate at different speeds. 4MATIC continually monitors the speed of each wheel to know when it's turning at the proper speed, or not, in every situation.

Stable
The vehicle remains stable at all times no matter how power is distributed across the four wheels. Light and nimble or powerful and efficient, 4MATIC is the perfect traveling companion for all seasons."

If looking to reject a car then I would be looking to this incorrect advertising IMHO.

 

[Dryce]

If looking to reject a car then I would be looking to this incorrect advertising IMHO.

I suspect not - they're not very precise about the claims.

 

[Dryce]

Which leaves us with the prime candidate for transmission wind up [ front to rear- not side to side!] IF!!! the centre differential is locked or close enough to locked meaning the front and rear wheels can't rotate at sufficiently different speeds while necessarily tracing out their different radius curves.

The suggestion with the GLC is that its particular 4Matic variant uses a multiplate clutch to control the torque to the front wheels..

My recollection of these things in motorcycles when cold was that they could be quite 'sticky'.

 

[dejongj]

It is interesting to see that on social media several GLC owners are coming forward who don't have this issue AT ALL. Nothing at all.

I find this very interesting, since;
a) Mercedes says it is a characteristic and they all do it. Hmm if some don't then they don't all do it and then surely it isn't a characteristic.
b) When pushing Mercedes customer services and say ALL GLC do this, they go into defence and they say not all of them do it. So it is a characteristic and normal or is it not?

Personally I couldn't care less whether it is or isn't, I know I don't want a car that does this to this extend.

PS. I think their PR company is putting reports out now, if that is so then isn't it amazing they are willing to spend money on that but not on fixing it. Sure it is speculation, but if you asked me 2 months ago that Mercedes wouldn't be willing to look into a reported issue I would have been in disbelief as well.

 

[JMitch84]

...strange noises from behind the dash a few minutes after start...

Does it sound like an electronic "chirp chirp, chirp chirp"? And do you have Keyless Go?

If so I have the same thing in my A Class, and I've been told that it's the Keyless Go antenna checking for the key 4 minutes into each journey. I use it to gauge my progress each morning

 

[Riversider]

Taken from All Wheel Drive Explained | awd cars, 4x4 vehicles, 4wd trucks, 4motion, quattro, xDrive, SH-AWD, Haldex, Torsen, wiki - How it works

Assuming that the "differential lock" function on the same axle is taken care of by Mercedes usual selective braking via the antilock/stability control system then cross axle transmission wind up should not be a problem. On the front axle there might be steering scrub if true ackerman steering is not present [ i.e. each front steering wheel to be at a slightly different angle in order to trace out a slightly different curve radius]---- I guess when the wheel is driven this might present as a series jumps or clonks????

However- the front and rear wheels also have trace out a different curve radius. Again wheels on the same rear axle present no problem with an open diff.
Which leaves us with the prime candidate for transmission wind up [ front to rear- not side to side!] IF!!! the centre differential is locked or close enough to locked meaning the front and rear wheels can't rotate at sufficiently different speeds while necessarily tracing out their different radius curves.
My theory is that some sort of effect like this may be exacerbated by the 39/61 torque split if indeed LHD cars don't suffer from this with their 45/55 split ?

While for driving on grippy pavement at slow manoeuvering speed at full lock it might be useful to program the centre diff to disengage at high steering angles its possible to envisage this as a situation where full 4WD might be very advantagous when trying to manoeuvre/ start off on very slippery /snowy conditions. Its perhaps the sort of ability lots of owners would expect ---nay demand from their 4WD vehicle. In the old days all these differential locking actions were manually selected by the driver as appropriate to conditions but now its all automatic meaning perhaps there has to be compromise somewhere.


or something like that.

Not sure I understand that but how does this account for the problem not (or less frequently) occurring at temperatures above +7 degrees?

 

[JohnM]

Seems like warmer weather -> better tyre grip -> clutch in centre diff gives instead of tyre slipping. Colder weather -> less tyre grip -> clutch stays locked and tyre slips instead. Hence suggestion for winter tyres to increase grip at the tyre.

 

[Tony Mac]

Seems like warmer weather -> better tyre grip -> clutch in centre diff gives instead of tyre slipping. Colder weather -> less tyre grip -> clutch stays locked and tyre slips instead. Hence suggestion for winter tyres to increase grip at the tyre.

Makes a lot of sense John, but doesn't answer why LHD owners do not appear to be experiencing / complaining about the same problem - is there a design difference in the Diff?

Also, is the clutch staying locked due to minor climate fluctuations an acceptable characteristic or a design fault?

In my opinion our RHD GLC's have a different diff design that is faulty, and fitting softer winter tyres simply masks the problem, that MB are hiding from. Would be good if there was LHD GLC in the UK on standard tyres, that could be compared against.